Astronomers have spotted a rare giant ‘blinking’ star towards the centre of the Milky Way. The team believes the serendipitous discovery, which came after 17 years of observation, represents another example of a rare class of ‘blinking giant’ stars that represents an eclipsing binary system.
The giant star with a mass around 100 times that of the Sun–designated VW-WIT-08–was spotted by the international team of researchers as it decreased in brightness by a factor of 30. A dimming extreme enough to result in the star almost disappearing entirely from the sky.
Changes in brightness such as this are usually associated with stars that pulsate or stars that exist in a binary system and are eclipsed by their companion star.
This giant star, which is located around 25,000 light-years away from Earth, dimmed for a period of several months in 2013 and then lightened again. A characteristic not commonly associated with the dimming mechanisms listed above.
The team of astronomers that have been investigating VW-WIT-08 believe that the dimming it demonstrated eight years ago and has not repeated since is the result of an as-of-yet unseen object orbital companion eclipsing the giant star.
They add that this eclipsing object could be another star or a planet, but one thing that is fairly certain is that it is surrounded by some form of an opaque disc which is responsible for causing the star’s extreme dimming.
“It’s amazing that we just observed a dark, large and elongated object pass between us and the distant star, and we can only speculate what its origin is,” says Sergey Koposov from the University of Edinburgh.
Alongside Leigh Smith from the Institute of Astronomy, the University of Cambridge, and Philip Lucas from the University of Hertfordshire, Koposov is one of the authors of a paper detailing the discovery published in the journal Monthly Notices of the Royal Astronomical Society.
VW-WIT-08 isn’t the only example of a star dimming in this unusual fashion, but arguably it is the most extreme example discovered thus far.
What’s Going On with Giant Blinking Stars?
Another example of this form of an eclipsing binary system is Epsilon Aurigae, first discovered in 1821 by German astronomer Johann Heinrich Fritsch. The visible component of this binary system is the supergiant star Almaaz–an Arabic name meaning the he-goat–which dims by around 50% every 27 years.
Though this dimming is less pronounced than that of VW-WIT-08, it lasts for a prolonged period of time; between 640 and 730 days–around two years. This means the dimming component of this binary system must be something truely immense, probably another star surrounded by a thick ring of obscuring dust, angled edge-on from our perspective.
Whilst this two-year eclipse which last occurred between 2009 and 2011 may seem extreme, it’s topped by the eclipse seen in another similar system discovered more recently–TYC 2505-672-1 found around 10,000 light-years from Earth.
This system currently holds the record for the longest known eclipse. Every 69 years the massive star component of this system is dimmed by a magnitude of 4.5 for a period of around 3 and a half years.
Thanks to the team that found VW-WIT-08 the catalogue of these eclipsing binary systems looks set to expand as the astronomers have currently found two more giant blinking stars ripe for further investigation.
“Occasionally we find variable stars that don’t fit into any established category, which we call ‘what-is-this?’, or ‘WIT’ objects,” remarks Lucas. “We really don’t know how these blinking giants came to be.”
What Does the Future Hold for Giant Blinking Stars?
The team made the discovery of VVV-WIT-08 using data collected by VISTA Variables , part of the Via Lactea (VVV Survey) which ran from 2010 to 2016. The survey’s main mission was the observation of the Milky Way’s central bulge and southern disc in near-infrared. The project utilised the capabilities of the VISTA telescope located at the Parnal Observatory, Chile.
Lucas adds: “It’s exciting to see such discoveries from VVV after so many years planning and gathering the data.”
The dimming of VVV-WIT-08 was also captured by the Gravitational Lensing Experiment (OGLE) operated by researchers at the University of Warsaw. Our galaxy’s central bulge was also a primary target for OGLE which makes its observations in light closer to the visible range of the electromagnetic spectrum.
The main advantage of OGLE is the fact that it makes frequent observations, something that was vital for building a model of VVV-WIT-08. This combination of observations also showed the astronomers that the giant star dims in both the visible spectrum and the infrared spectrum.
The team’s findings show that there are undoubtedly more eclipsing binary systems in the Milky Way left to be discovered. But this may not be the most difficult part of the process of investigating these systems.
“There are certainly more to be found, but the challenge now is in figuring out what the hidden companions are, and how they came to be surrounded by discs, despite orbiting so far from the giant star,” Smith concludes. “In doing so, we might learn something new about how these kinds of systems evolve.”
The Oort Cloud, the most distant region of our solar system, was discovered by Jan Hendrik Oort. It is a giant structure composed of billions (if not trillions) of relatively small icy and rocky objects, and unlike the rest of our solar system (which is flat like a disc), it is believed that the Oort Cloud is spherical.
Now, astronomers from the Leiden Observatory produced the first simulation to display the formation and early evolution of the cloud.
The theories that tried to describe the Oort cloud evolution are scattered and hard to reconcile. Some focus more on the formation, others are more concerned with the relation with the Sun’s position within our galaxy. The Leiden team connected different parts of those theories and simulated the development of the cloud over one billion years.
To get to the origins of the Oort cloud, we need to get to the origins of our solar system. The solar system started in a messy dusty fog suspended around the Sun. The planets and everything in the solar system formed by coagulating everything gravitationally around 4.5 billion years ago. That is an important part of the story, because if formed too early or too late, the Oort cloud couldn’t be formed. The best scenario is the one in which the Sun escapes its star cluster just in the best moment to avoid losing too many objects, thus allowing the formation of the Oort cloud.
Other crucial events needed to take place to enable the formation of the structure. Multiple encounters with passing stars and Milky Way tidal gravitational effects all played a role, helping the Oort cloud take shape some 100 million years after the Sun had escaped its star cluster.
These processes can party be seen in the below animation. In the animation, the Sun is orbiting the galactic center, passing near a sea of asteroids which are ejected by hypothetical planets from other systems, resulting in the Oort cloud.
The opposite process can also happen though — too many interactions with other systems and the galaxy can cause the loss of many objects, which would then end up in interstellar space. That’s also the possible origin of the free-floating Oumuamua that caused quite a lot of stir as it passed by our solar system.
Asteroids from the conveyor belt can also pass through the orbit of the giant planets, Jupiter, Saturn, Uranus, Neptune. These objects are placed in an irregular orbit and they can have a periodic relationship with Jupiter and Saturn, called orbital resonance. The resonance creates a chaotic environment for them, and some are kicked to a different orbit.
However, the gas giants could not have contributed much to the formation of the Oort cloud. The study has shown that their ejection timescale is much too short to contribute significantly.
Another important takeaway from the study is the simulation of a single asteroid life. The scientists depicted the evolution of an asteroid that had a resonance interaction with Jupiter. Due to this resonance, its orbit is successively altered for 2 million years. You can see the timescale increasing significantly and also the shocking increase of distance from Neptune’s orbit (in red).
In the end, asteroids from the conveyor belt by the giants alongside complex interactions with tidal forces from our galaxy helped form the Oort cloud. The same phenomenon caused the reentry of 0.2 to 0.6 objects a year. Moreover, the Sun’s orbit near a sea of Oort cloud from neighbouring stars may have caused the kidnapping of many objects, such as Sedna.
The original study can be found in the preprint for Astronomy & Astrophysics. Concerned about environmental impacts, the authors added the energy consumption to produce such a long simulation: “This results in about 2MWh of electricity http://green-algorithms.org/), consumed by the Dutch National supercomputer.”
Astronomers have completed the first in-depth census of molecular clouds in the nearby Universe. The study has revealed that these star-forming regions not only look different but also behave differently. This finding runs in opposition to previous scientific consensus, which considered these clouds of dust and gas to be fairly uniform.
The project–Physics at High Angular Resolution in Nearby GalaxieS (PHANGS)–consisted of a systematic survey of 100,000 molecular clouds in 90 galaxies in the local Universe. The primary aim of the PHANGS was to get an idea of how these star-forming regions are influenced by their parent galaxies.
The census was conducted with the use of the Atacama Large Millimeter/ submillimeter Array (ALMA) located on the Chajnantor plateau, in the Atacama Desert of northern Chile. Whilst not marking the first time stellar nurseries have been studied with ALMA, this is the first census of its kind to observe globular clusters across more than either one galaxy or a small region of a single galaxy.
“We have carried out the first real ‘census’ of these stellar nurseries, and it provided us with details about their masses, locations, and other properties,” Adam Leroy, Associate Professor of Astronomy at Ohio State University (OSU) tells ZME Science. “Some people thought that all stellar nurseries across every galaxy look more or less the same, and it took having a really big, sensitive, and high-resolution survey of many galaxies with a telescope such as ALMA to see that this is not the case. This survey allows us to see how the stellar nurseries change across different galaxies. “
As a result, this is the first time that astronomers have been granted a look at the ‘big picture’ when it comes to these star-forming regions. Erik Rosolowsky, Associate Professor of Physics at the University of Alberta, and a co-author of the research points out that what ALMA has allowed the team of astronomers to create is essentially a new form of ‘cosmic cartography’ consisting of 90 maps of unparalleled detail detailing the regions of space where the next generation of stars will be born.
“By doing this we will combine what we are learning from ALMA about the clouds that form stars with pictures of newly formed stars from these other telescopes. This promises to give us the best view ever of the full life cycle of these stellar nurseries, and our most complete picture ever of the full cycle of star birth and death.”
“Our survey is the first one to capture the demographics of these stellar nurseries across a large number of the galaxies near the Milky Way,” adds Leroy, the lead author of a paper presenting the PHANGS ALMA survey. “We used these measurements to measure the characteristics of these nurseries, their lifetimes, and the ability of these objects to form new stars.”
How Galactic Neighborhoods Influence Star-Forming Clouds
The variety displayed by the molecular clouds surveyed in the PHANGS project was visible due to ALMA’s ability to take millimeter-wave images with the same sharpness and quality as images taken in the visible spectrum.
“While optical pictures show us light from stars, these ground-breaking new images show us the molecular clouds that form those stars,” says Leroy. “That helped us to see that stellar nurseries actually change from place to place.”
The team compared the changes displayed by molecular clouds from galaxy to galaxy to changes in houses, neighbourhoods and cities from region to region here on Earth.
“How stellar nurseries relate to their parent galaxies has been a big question for a long time. We’re able to answer this because our survey expands the amount of data on stellar nurseries by a factor of almost 100,” says Leroy. “Before this, it was very common to study a few hundred nurseries in one galaxy. So it was kind of like trying to learn about houses in general by looking only at neighbourhoods in Columbus, Ohio.
“You will learn some things about houses, but you miss the big picture and a lot of the variation, complexity, and commonality With this survey we looked at houses in many cities across many countries.”
Adam Leroy, Ohio State University
Leroy continues by explaining that stellar nurseries ‘know’ about their neighbourhood, meaning that molecular clouds are different depending on what galaxy they live in or where in that galaxy they are located. “So the stellar nurseries that we see in the Milky Way won’t be the same as those in a different galaxy, and the stellar nurseries in the outer part of a galaxy–where we live–aren’t the same as those near the galaxy centre.”
The team found clouds in the dense central regions of galaxies tend to be more massive, denser, and more turbulent than those located on the outskirts of a galaxy. In addition to this, the census revealed the lifecycle of clouds also depends on their environment. Annie Hughes, an astronomer at L’Institut de Recherche en Astrophysique et Planétologie (IRAP) explains that this means that both the rate at which a cloud forms stars and the processes that ultimately destroy clouds both seem to depend on where the cloud lives.
How Differences in Globular Clusters Influence the Birth of Stars
Because all stars are formed in molecular clouds, understanding the differences in these clouds of gas and dust and how they are caused by the conditions in which they exist is key to better understanding the processes that are driving the birth of stars like our own Sun.
These molecular clouds are so vast that they can birth anywhere from thousands to hundreds of thousands of stars before being exhausted of raw materials. These new observations have shown astronomers that each cosmic neighbourhood can have an effect on where stars are born and how many stars are spawned.
“Every star in the sky, in fact, every star in every galaxy, including our Sun, was born in one of these stellar nurseries. These are really the engines that build galaxies and make planets, and they’re just an essential part of the story of how we got here.”
Adam Leroy, Ohio State University
The next step for the astronomers will be to combine the data provided by ALMA with surveys conducted by other telescopes including the Hubble space telescope, and the Very Large Telescope (VLT) also located in the Atacama desert, Chile. Leroy hopes that this along with observations made with the James Webb Space Telescope (JWST), will help astronomers answer the question of how the diversity of molecular structures affects the stars which form within them. He explains: “By doing this we will combine what we are learning from ALMA about the clouds that form stars with pictures of newly formed stars from these other telescopes.
This promises to give us the best view ever of the full life cycle of these stellar nurseries, and our most complete picture ever of the full cycle of star birth and death.”
Adam Leroy, Ohio State University
Leroy concludes by pointing out why the study of these star-forming regions is so important. “This is the first time we have gotten a clear view of the population of these stellar nurseries across the whole nearby universe,” the researcher says. “It’s a big step towards understanding where we come from.”
Whilst it may not have the snappiest name, the event GW150914 is pretty significant in terms of our understanding of the Universe. This event, with a name that includes ‘GW’ as a prefix which is an abbreviation of ‘Gravitational Wave’ and the date of observation–15/09/14– marked humanity’s first direct detection of gravitational waves.
This was groundbreaking on two fronts; firstly it successfully confirmed a prediction made by Albert Einstein’s theory of general relativity almost a century before. A prediction that stated events occurring in the Universe do not just warp spacetime, but in certain cases, can actually send ripples through this cosmic fabric.
The second significant aspect of this observation was the fact that it represented an entirely new way to ‘see’ the Universe, its events and objects. This new method of investigating the cosmos has given rise to an entirely new form of astronomy; multimessenger astronomy. This combines ‘traditional’ observations of the Universe in the electromagnetic spectrum with the detection of gravitational waves, thus allowing us to observe objects that were previously invisible to us.
Thus, the discovery of gravitational waves truly opened up an entirely new window on the cosmos, but what are gravitational waves, what do they reveal about the objects that create them, and how do we detect such tiny tremblings in reality itself?
Gravitational Waves: The Basics
Gravitational waves are ripples in the fabric of spacetime.
These ripples travel from their source at the speed of light.
The passage of gravitational waves squash and stretch space itself.
Gravitational waves can be detected by measuring these infinitesimally small changes in the distance between objects.
They are created when an object or an event that curves spacetime causes that curvature to change shape.
Amongst the causes of gravitational waves are colliding black holes and neutron stars, supernovae, and stars that are undergoing gravitational collapse.
Imagine sitting at the side of a lake, quietly observing the tranquil surface of the water undisturbed by nature, the wind, or even by the slightest breeze. Suddenly a small child runs past hurling a pebble into the lake. The tranquillity is momentarily shattered. But, even as peace returns, you watch ripples spread from the centre of the lake diminishing as they reach the banks, often splitting or reflecting back when they encounter an obstacle.
The surface of the lake is a loose 2D analogy for the fabric of spacetime, the pebble represents an event like the collision of two black holes, and our position on Earth is equivalent to a blade of grass on the bank barely feeling the ripple which has diminished tremendously in its journey to us.
Gravitational waves were first predicted by Henri Poincare in 1905 as disturbances in the fabric of spacetime that propagate at the speed of light, but it would take another ten years for the concept to really be seized upon by physicists. This happened when Albert Einstein predicted the same phenomenon as part of his revolutionary 1916 geometric theory of gravity, better known as general relativity.
Whilst this theory is most well-known for suggesting that objects with mass would cause warping of spacetime, it also went a step further positing that an accelerating object should change this curvature and cause a ripple to echo through spacetime. Such disturbances in spacetime would not have been permissible in the Newtonian view of gravity which saw the fabric of space and time as separate entities upon which the events of the Universe simply play out.
But upon Einstein’s dynamic and changing stage of united spacetime, such ripples were permissible.
Gravitational waves arose from the possibility of finding a wave-like solution to the tensor equations at the heart of general relativity. Einstein believed that gravitational waves should be generated en masse by the interaction of massive bodies such as binary systems of super-dense neutron stars and merging black holes.
The truth is that such ripples in spacetime should be generated by any accelerating objects but Earth-bound accelerating objects cause perturbations that are far too small to detect. Hence why our investigations must turn to areas of space where nature provides us with objects that are far more massive.
As these ripples radiate outwards from their source in all directions and at the speed of light, they carry information about the event or object that created them. Not only this, but gravitational waves can tell us a great deal about the nature of spacetime itself.
Where do Gravitational Waves Come From?
There are a number of events that can launch gravitational waves powerful enough for us to detect with incredibly precise equipment here on Earth. These events are some of the most powerful and violent occurrences that the Universe has to offer. For instance, the strongest undulations in spacetime are probably caused by the collision of black holes.
Other collision events are associated with the production of strong gravitational waves; for example the merger between a black hole and a neutron star, or two neutron stars colliding with each other.
But, a cosmic body doesn’t always need a partner to make waves. Stellar collapse through supernova explosion–the process that leaves behind stellar remnants like black holes and neutron stars– also causes the production of gravitational waves.
To understand how gravitational waves are produced, it is useful to look to pulsars–binary systems of two neutron stars that emit regular pulses of electromagnetic radiation in the radio region of the spectrum.
Einstein’s theory suggests that a system such as this should be losing energy by the emission of gravitational waves. This would mean that the system’s orbital period should be decreasing in a very predictable way.
The stars draw together as there is less energy in the system to resist their mutual gravitational attraction, and as a result, their orbit increases in speed, and thus the pulses of radio waves are emitted at shorter intervals. This would mean that the time it takes for the radio wave to be directly facing our line of sight would be reduced; something we can measure.
This is exactly what was observed in the Hulse-Taylor system (PSR B1913±16), discovered in 1974, which is comprised of two rapidly rotating neutron stars. This observation earned Russell A. Hulse and Joseph H. Taylor, Jr, both of Princeton University, the 1993 Nobel Prize in Physics. The reason given by the Nobel Committee was: “for the discovery of a new type of pulsar, a discovery that has opened up new possibilities for the study of gravitation.”
Though inarguably an impressive and important scientific achievement, this was still only indirect evidence of gravitational waves. Whilst the effect Einstein predicted of shortening of the pulsar’s spin was definitely present, this wasn’t an actual direct detection.
In fact, though not alive to witness this momentous achievement, Einstein had predicted that this would be the only way we could ever garner any hint of gravitational waves. The great physicist believed those spacetime ripples would be so faint that they would remain impossible to detect by any technological means imaginable at that time.
Fortunately, Einstein was wrong.
How do we Detect Gravitational Waves?
It should come as no surprise that actually detecting a gravitational wave requires a piece of equipment of tremendous sensitivity. Whilst the effect of gravitational waves–the squashing and stretching space itself–sounds like something that should pre-eminently visible, the degree by which this disturbance occurs is so tiny it is totally imperceptible.
Fortunately, there is a branch of physics that is pretty adept at deal with the tiny. To spot gravitational waves, researchers would use an effect called interference, something demonstrated in the most famous quantum physics experiment of all time; the double-slit experiment.
Physicists realised that a laser interferometer could be used to measure the tiny squashing and stretching of space as it would cause the arms of the equipment to shrink by a minute amount. This means when splitting a laser and sending it through the arms of an interferometer the squeezing of space caused by the passage of a gravitational wave would cause one laser to arrive slightly ahead of the other–meaning they are out of phase and causing destructive interference. Thus, this difference in arrival times causes interference that gives an indication that gravitational waves have rippled across one of the arms.
But, not just any laser interferometer would do. Physicists would need an interferometer so large that it constituents a legitimate feat in engineering. Enter the Laser Interferometer Gravitational-wave Observatory (LIGO).
The LIGO detector uses two laser emitters based at the Hanford and Livingstone observatories, separated by thousands of kilometres apart to form an incredibly sensitive interferometer. From these emitters, lasers are sent down the ‘arms’ of the interferometer which are actually 4km long vacuum chambers.
This results in a system that is so sensitive it can measure a deviation in spacetime that is as small as 1/10,000 the size of an atomic nucleus. To put this into an astronomical context; it is equivalent to spotting a star at a distance of 4.2 light-years and pinpointing its location to within the width of a human hair! This constitutes the smallest measurement ever practically attempted in any science experiment.
And in 2015, this painstaking operation paid off.
On 14th September 2015, the LIGO and Virgo collaboration spotted a gravitational wave signal emanating from the spiralling in and eventual merger of two black holes, one 29 times the mass of the Sun, the other 36 times our star’s mass. From changes in the signal received the scientists were also able to observe the resultant single black hole.
The signal, named GW150914, represented not just the first observation of gravitational waves, but also the first time humanity had ‘seen’ a binary stellar-mass black hole system, proving that such mergers could exist in the Universe’s current epoch.
Different Kinds of Gravitational Waves
Since the initial detection of gravitational waves, researchers have made a series of important and revelatory detections. These have allowed scientists to classify different types of gravitational waves and the objects that may produce them.
Continuous Gravitational Waves
A single spinning massive object like a neutron star is believed to cause a continuous gravitational wave signal as a result of imperfections in the spherical shape of this star. if the rate of spin remains constant, so too are the gravitational waves it emits–it is continuously the same frequency and amplitude much like a singer holding a single note. Researchers have created simulations of what an arriving continuous gravitational wave would sound like if the signal LIGO detected was converted into a sound.
The sound of a continuous gravitational wave of the kind produced by a neutron star can be heard below.
Compact Binary Inspiral Gravitational Waves
All of the signals detected by LIGO thus far fit into this category as gravitational waves created by pairs of massive orbiting objects like black holes or neutron stars.
The sources fit into three distinct sub-categories:
Binary Black Hole (BBH)
Binary Neutron Star (BNS)
Neutron Star-Black Hole Binary (NSBH)
Each of these types of binary pairing creates its own unique pattern of gravitational waves but shares the same overall mechanism of wave-generation–inspiral generation. This process occurs over millions of years with gravitational waves carrying away energy from the system and causing the objects to spiral closer and closer until they meet. This also results in the objects moving more quickly and thus creating gravitational waves of increasing strength.
The ‘chirp’ of an eventual merger between neutron stars has been translated to sound waves and can be heard below.
Stochastic Gravitational Waves
Small gravitational waves that even LIGO is unable to precisely pinpoint could be passing over Earth from all directions at all times. These are known as stochastic gravitational waves due to their random nature. At least part of this stochastic signal is likely to have originated in the Big Bang.
Should we eventually be able to detect this signal it would allow us to ‘see’ further back into the history of the Universe than any electromagnetic signal could, back to the epoch before photons could freely travel through space.
The simulated sound of this stochastic signal can be heard below.
It is extremely likely given the variety of objects and events in the Universe that other types of gravitational wave signals exist. This means that the quest to detect such signals is really an exploration of the unknown. Fortunately, our capacity to explore the cosmos has been boosted tremendously by our ability to detect gravitational waves.
A New Age of Astronomy
GW150914 conformed precisely to the predictions of general relativity, confirming Einstein’s most revolutionary theory almost exactly six decades after his death in 1955. That doesn’t mean that gravitational waves are done teaching us about the Universe. In fact, these ripples in spacetime have given us a whole new way to view the cosmos.
Before the discovery of gravitational waves, astronomers were restricted to a view of the Universe painted in electromagnetic radiation and therefore our observations have been confined to that particular spectrum.
Using the electromagnetic spectrum alone, astronomers have been able to discover astronomical bodies and even thecosmic microwave background (CMB) radiation, a ‘relic’ of one of the very first events in the early universe, the recombination epoch when electrons joined with protons thus allowing photons to begin travelling rather than endlessly scattering. Therefore, the CMB is a marker of the point the universe began to be transparent to light.
Yet despite the strides traditional astronomy has allowed us to make in our understanding of the cosmos, the use of electromagnetic radiation is severely limited. It does not allow us to directly ‘see’ black holes, from which light cannot escape. Nor does it allow us to see non-baryonic, non-luminous dark matter, the predominant form of matter in galaxies–accounting for around 85% of the universe’s total mass. As the term ‘non-luminous’ suggests dark matter does not interact with the electromagnetic spectrum, it neither absorbs nor emits light. This means that observations in the electromagnetic spectrum alone will never allow us to see the majority of the matter in the universe.
Clearly, this is a problem. But one that can be avoided by using the gravitational wave spectrum as both black holes and dark matter do have considerable gravitational effects.
Gravitational waves also have another significant advantage over electromagnetic radiation.
This new form of astronomy measures the amplitude of the travelling wave, whilst electromagnetic wave astronomy measures the energy of the wave, which is proportional to the amplitude of the wave squared.
Therefore the brightness of an object in traditional astronomy is given by 1/distance² whilst ‘gravitational brightness’ falls off by just 1/distance. This means that the visibility of stars persists in gravitational waves for a much greater distance than the same factor persists in the electromagnetic spectrum.
Of course, none of this is to suggest that gravitational wave astronomy will ‘replace’ traditional electromagnetic spectrum astronomy. In fact the two are most powerful when they are unified in an exciting new discipline–multimessenger astronomy
Sources and Further Reading
Maggiore. M., Gravitational Waves: Theory and Experiments, Oxford University Press, 
Maggiore. M., Gravitational Waves: Astrophysics and Cosmology, Oxford University Press, 
Collins. H., Gravity’s Kiss: The Detection of Gravitational Waves, MIT Press, 
The Dark Energy Survey (DES) is an ambitious cosmological project that aims to map hundreds of millions of galaxies. In the process, the project will detail hundreds of millions of galaxies, observe thousands of supernovae, map the cosmic web that links galaxies, all with the aim of investigating the mysterious force that is causing the Universe to expand at an accelerating rate.
Using the 570-megapixel Dark Energy Camera on the National Science Foundation’s Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory (CTIO), Chile, the DES has observed a map of galaxy distribution and morphology that stretches 7 billion light-years and captures 1/8 of the sky over Earth.
Now new results from the DES which collects the work of an international team of over 400 scientists from over 25 institutions from countries including the US, UK, France, Spain, Brazil, and Australia, are in. The findings are detailed in a ground-breaking series of 29 papers and comprises of data collected during the DES’ first three years of operation providing the most detailed description of the Universe’s composition and expansion to date.
The survey was conducted between 2013 to 2019 cataloging hundreds of millions of objects, with the three years of data covered in these papers alone containing observations of at least 226 million galaxies observed over 345 nights.
The fact that some of these galaxies are close to the Milky Way and others are much more distant–up to 7 billion light-years away– gives researchers an excellent picture of the evolution of the Universe over around half of its lifetime.
The results seem to confirm the standard model of cosmology, currently the best-evidenced theory of the Universe’s composition and evolution which suggests the Universe was created in a ‘Big Bang’ event and has a composition of 5% ordinary or baryonic matter, 27% dark matter, and 68% dark energy.
The snapshot of the Universe provided by the DES does seem to show that the Universe is less ‘clumpy’ than current cosmological models suggest, however.
Illuminating the Dark Universe
The fact that the ‘Dark Universe’ consists of 95% of the matter and energy in the known cosmos means that there are huge gaps in our understanding of the evolution of the Universe, its past, present, and its future.
These gaps include the nature of dark matter, whose gravitational influence holds galaxies together, and dark energy, the force that is expanding space between the galaxies driving them apart at an accelerating rate.
These effects seem to be in opposition, with one holding matter together and the other working upon space itself to drive matter apart. And it is this cosmic struggle that shapes the Universe which the DES aimed to investigate.
There are two key phenomena which the survey used to do this. Studying ‘the cosmic web’ that links galaxies together in clusters and loose associations gives hints at the distribution and influence of dark matter.
The second phenomenon used by the DES is the bending of light as it travels past curvatures in spacetime created by objects of tremendous mass like galaxies. This effect predicted by Einstein’s theory of gravity–general relativity–is known as ‘gravitational lensing.’
The DES relied on a form of this effect called ‘weak gravitational lensing’ to assess how dark matter is distributed across the Universe, thus inferring its ‘clumpiness.’
The data collected by the DES was cross-referenced against measurements carried out by the European Space Agency (ESA) operated mission, the Planck observatory. The orbiting observatory, which operated between 2009 and 2013 and studied the cosmic background radiation (CMB)–an imprint leftover from an event shortly after the Big Bang in which electrons and protons connected thus allowing photons to travel freely for the first time.
Observing the CMB reveals conditions that were ‘frozen in’ to it at the time of this event known as the last scattering and thus gives a detailed picture of the Universe when it was just 400 thousand years old for the DES team to draw from.
Setting the Scene for Future Surveys
The DES intensely studied ten regions labeled as ‘deep fields’ which were repeatedly imaged during the course of the survey. These images were stacked which allowed astronomers to observe distant galaxies.
In addition to allowing researchers to see further into the Universe and thus further back in time, information regarding redshift– an increase in wavelength caused by objects receding which can arise as a result of the Universe’s expansion–taken from these deep fields was used to calibrate the rest of the survey. This constituted a major step forward for cosmic surveys providing the researchers with a picture of the Universe painted with stunning precision.
Whilst the DES was concluded in 2019, the sheer wealth of data collected by the survey requires a huge amount of computing power and time to assess. This is why we are only seeing the first three years of observations reported and likely means that the DES still has much more to deliver.
This will ultimately set the scene for the Legacy Survey of Space and Time (LSST) which will be conducted at the Vera C Rubin observatory–currently under construction on the El Penon peak of Cerro Pachon in northern Chile.
Whereas the DES surveyed an inarguably impressive 1/8 of the sky over the earth, the wide-field camera that will conduct the LSST will capture the entire sky over the Southern hemisphere, meaning it will view half of the entire sky over our planet.
A major part of the LSST’s mission will be the investigation of dark matter and dark energy, meaning that when the data from the DES is finally exhausted and its secrets are revealed, a worthy successor will be waiting in the wings to assume its mission of discovery.
Using data collected by the Very Large Telescope (VLT) a team of astronomers has discovered iron and nickel in the atmosphere of around 20 different solar system comets–including some located far away from the Sun.
These findings will come as a surprise to astronomers because even though such heavy metals have been known to exist in solid form within comet interiors before, the vapour of such elements has only previously been associated with cometary atmospheres in hot environments.
This is the first time such vapour has been seen in the cooler atmospheres of comets that exist far from a star and could indicate some previously unknown mechanism or material on the surface of comets.
“It was a big surprise to detect iron and nickel atoms in the atmosphere of all the comets we have observed in the last two decades, about 20 of them, and even in ones far from the Sun in the cold space environment,” says Jean Manfroid, of the University of Liège, Belgium.
This wasn’t the only surprise the team found, however. The Belgian astronomers–who have been studying comets with the VLT for 20 years–observed nickel and iron in the atmosphere of the comet in equal amounts.
Generally, iron is about ten times more abundant in the solar system than nickel, and comets are believed to be material left over from the formation of planetary bodies within the solar system. That means it’s something of a mystery why the comets the team observed should have such a relatively large abundance of nickel.
“Comets formed around 4.6 billion years ago, in the very young Solar System, and haven’t changed since that time. In that sense, they’re like fossils for astronomers,” Emmanuel Jehin, also from the University of Liège. “This discovery went under the radar for many years.”
Manfroid and Jehin are two of the authors of a paper published in the latest edition of the journal Nature documenting the team’s findings. And that isn’t the only research revealing metal in the atmosphere of such a body published in Nature this month.
The discovery is accompanied by the revelation that a separate team of researchers, this time located in Poland, has also found traces of nickel vapour in the atmosphere around the interstellar visitor 2l/Borisov.
This comet may sound familiar as it made headlines in 2019 when it became only the second object found within the solar system which originated from outside our planetary system.
A paper detailing this second finding is also published in this month’s Nature.
Heavy Metal Rocks
Astronomers have known for some time that a variety of metals exist within the icy and rocky interiors of comets. There have even been suggestions that spent comets could be mined for precious or useful metals like gold, silver, platinum and iron.
These solid metals within comets were not expected to be found as gases in the body’s atmosphere, though, unless that body is passing within close vicinity to a star.
It is the heat from these close brushes with stars like the Sun that causes solid metals within comets to ‘sublimate’–the process by which solid material changes directly into a gaseous state.
That means that distant comets in the cold environment of space away from the heat of the Sun shouldn’t have heavy metal atmospheres.
Yet, despite this, researchers have now found nickel and iron vapour in the atmospheres of comets up to 480 million kilometres from the Sun. A distance that is three astronomical units, or three times the distance between the Sun and the Earth.
In order to make this discovery, the team employed the technique of spectroscopy which reveals the signatures of specific chemical elements and the Ultraviolet and Visual Echelle Spectrograph (UVES) instrument on the VLT to assess the chemical composition of comets’ atmospheres.
The spectral lines of nickel and iron found by the team in comets’ atmospheres were extremely faint, which leads them to believe that the reason such elements have been missed in past is due to their tiny abundance. The team says that for every 100kg of water in the atmosphere of the comets they studied there is just one gram of iron and nickel respectively.
The Belgian astronomers believe that the equal amounts of iron and nickel together with the sublimation at low temperatures means there is something undiscovered at the surface of the comets they studied.
“Usually there is 10 times more iron than nickel, and in those comet atmospheres we found about the same quantity for both elements,” explains Damien Hutsemékers, also a member of the Belgian team from the University of Liège.”We came to the conclusion they might come from a special kind of material on the surface of the comet nucleus, sublimating at a rather low temperature and releasing iron and nickel in about the same proportions.”
The team intends to attempt to use new telescope technology such as the Mid-infrared ELT Imager and Spectrograph (METIS) on ESO’s upcoming Extremely Large Telescope (ELT)–currently under construction in the Atacama Desert region of Northern Chile– to discover what this material is.
The findings of this team are accompanied by the revelation that nickel vapour has also been discovered in the atmosphere of 2I/Borisov.
2I/Borisov: The Interstellar Intruder that keeps giving
The discovery that metal is also present in the atmosphere of the interstellar visitor 2I/Borisov was made by a team of astronomers in Poland. The team also used the VLT to catch a glimpse of the interstellar comet as it passed through the solar system.
The data collected with the VLT’s X-Shooter spectrograph revaled nickel vapour in the cold envlope surround 2I/Borisov.
ESO/L. Calçada/O. Hainaut, P. Guzik and M. Drahus
The discovery marks another surprise for astronomers, as again it details the discovery of sublimated heavy metals in a cold atmosphere.
“At first we had a hard time believing that atomic nickel could really be present in 2I/Borisov that far from the Sun,” says Piotr Guzik, the Jagiellonian University, Poland, a co-author on this second study. “It took numerous tests and checks before we could finally convince ourselves.”
This latter study shows that nickel was not uniquely present during the formation of our solar system, but as it can be seen in a comet from another planetary grouping, it may well be common in many such conglomerations.
“All of a sudden we understood that gaseous nickel is present in cometary atmospheres in other corners of the Galaxy,” Michał Drahus, also from the Jagiellonian University and another of the paper’s co-authors, says.
In unison, both these studies indicate that the comets of this solar system and the interstellar visitor 2I/Borisov share many similarities. Dahus adds: “Now imagine that our Solar System’s comets have their true analogues in other planetary systems — how cool is that?”
Jehin, meanwhile, believes these studies could inspire future research into cometary bodies and their atmospheres, and a re-examination of data already collected.
“Now people will search for those lines in their archival data from other telescopes,” the University of Liège researcher concludes. “We think this will also trigger new work on the subject.”
Black holes are cosmic bodies that pack an immense amount of mass into a surprisingly small space. Due to their extremely intense gravity, nothing can escape their grasp — not even light which defines the universe’s speed limit.
April 10th, 2019 marked a milestone in science history when the team at the Event Horizon Telescope revealed the first image of a supermassive black hole. As a result, these areas of space created when stars reach the end of their nuclear fuel burning and collapse creating massive gravitational wells, completed their transition from theory to reality.
This transition has been further solidified since with the revelation of a second, much clearer image of the supermassive black hole (SMBH) at the centre of the galaxy Messier 87 (M87). This second image revealing details such as the orientation of the magnetic fields that surround it and drive its powerful jets that extend for light-years.
The study of black holes could teach us much more than about these spacetime events and the environments that home them, however. Because cosmologists believe that most galaxies have an SMBH sat at their centre, greedily consuming material like a fat spider lurking at the centre of a cosmic web, learning more about these spacetime events can also teach us how galaxies themselves evolve.
The origin of black holes is one that runs in reverse to that of most astronomical objects. We didn’t discover some mysterious object in the distant cosmos and then began to theorise about it whilst making further observations.
Rather, black holes entered the scientific lexicon in a way that is more reminiscent of newly theorised particles in particle physics; emerging first from the solutions to complex mathematics. In the case of black holes, the solutions to the field equations employed by Einstein in his most important and revolutionary theory.
Just as a physical black hole forms from the collapse of a star, the theory of black holes emerged from the metaphorical collapse of the field equations that govern the geometrical theory of gravity; better known as general relativity.
One of the most common misconceptions about black holes arises from their intrinsic uniqueness and the fact that there really isn’t anything else like them in the Universe.
That’s Warped: Black Holes and Their Effect on Spacetime
General relativity introduced the idea that mass has an effect on spacetime, a concept fundamental to the idea that space and time are not passive stages upon which the events of the universe play out. Instead, those events shape that stage. As John Wheeler brilliantly and simply told us; when it comes to general relativity:
“Matter tells space how to curve. Space tells matter how to move.”
The most common analogy is for this warping of space is that of placing objects on a stretched rubber sheet. The larger the object the deeper the ‘dent’ and the more extreme the curvature it creates. In our analogy, a planet is a marble, a star an apple, and a black hole a cannonball.
Thus, considering this a black hole isn’t really ‘an object’ at all but, is actually better described as a spacetime event. When we say ‘black hole’ what we really mean is an area of space that is so ‘warped’ by a huge amount of mass condensed into a finite point that even light itself doesn’t have the necessary velocity to escape it.
This point at which light can no longer escape marks the first of two singularities that define black holes–points at which solutions of the equations of general relativity go to infinity.
The Event Horizon and the Central Singularity
The event horizon of a black hole is the point at which its escape velocity exceeds the speed of light in vacuum (c). This occurs at a radius called the Schwarzchild radius–named for astrophysicist Karl Schwarzschild, who developed a solution for Einstien’s field equations whilst serving on the Eastern Front in the First World War.
His solution to Einstein’s field equations–which would unsurprisingly become known as the Schwarzschild solution– described the spacetime geometry of an empty region of space. It had two interesting features — two singularities — one a coordinate singularity the other, a gravitational singularity. Both take on significance in the study of black holes.
Dealing with the coordinate singularity, or the Schwarzchild radius first.
The Schwarzchild radius (Rs) also takes on special meaning in cases where the radius of a body shrinks within this Schwarzschild radius (ie. Rs >r). When a body’s radius shrinks within this limit, it becomes a black hole.
All bodies have a Schwarzschild radius, but as you can see from the calculation below for a body like Earth, Rs falls well-within its radius.
That’s part of what makes black holes unique; their Schwartzchild radius is outside their physical radius because their mass is compressed into such a tiny space.
Because the outer edge of the event horizon is the last point at which light can escape it also marks the last point at which events can be seen by distant observers. Anything past this point can never be observed.
The reason the Schwarzschild radius is called a ‘coordinate singularity’ is that it can be removed with a clever choice of coordinate system. The second singularity can’t be dealt with in this way. This makes it the ‘true’ physical singularity of the black hole itself.
This is known as the gravitational singularity and is found at the centre of the black hole (r=0). This is the end-point for every particle that falls into a black hole. It’s also the point the Einstein field equations break down… maybe even all the laws of physics themselves.
The fact that the escape velocity of the event horizon exceeds the speed of light means that no physical signal could ever carry information from the central singularity to distant observers. We are forever sealed off from this aspect of black holes, which will therefore forever remain in the domain of theory.
How to Make a Black Hole
We’ve already seen that for a body with the mass of Earth to become a black hole, its diameter would have to shrink to less than 2cm. This is obviously something that just isn’t possible. In fact, not even our Sun has enough mass to end its life as a black hole. Only stars with around three times the mass of the Sun are massive enough to end their lives in this way.
But why is that the case?
It won’t surprise you to learn that for an astronomical body to become a black hole it must meet and exceed a series of limits. These limits are created by outward forces that are resisting against the inward force that leads to gravitational collapse.
For planets and other bodies with relatively small masses, the electromagnetic repulsion between atoms is strong enough to grant them stability against total gravitational collapse. For large stars the situation is different.
During the main life cycle of stars–the period of the fusion of hydrogen atoms to helium atoms–the primary protection against gravitational collapse is the outward thermal and radiation pressures that are generated by these nuclear processes. That means that the first wave of gravitational collapse occurs when a star’s hydrogen fuel is exhausted and inward pressure can no longer be resisted.
Should a star have enough mass, this collapse forces together atoms in the nucleus enough to reignite nuclear fusion— with helium atoms now fusing to create heavier elements. When this helium is exhausted, the process happens again, with the collapse again stalling if there is enough pressure to trigger the fusion of heavier elements still.
Stars like the Sun will eventually reach the point where their mass is no longer sufficient to kick start the nuclear burning of increasingly heavier elements. But if it isn’t nuclear fusion that is generating the outward forces that prevent complete collapse, what is preventing these lower-mass stars from becoming black holes?
Placing Limits on Gravitational Collapse
Lower-mass stars like the Sun will end their lives as white dwarf stars with a black hole form out of reach. The mechanism protecting these white dwarfs against complete collapse is a quantum mechanical phenomenon calleddegeneracy.
This ‘degeneracy pressure’ is a factor of the Pauli exclusion principle, which states that certain particles– known as fermions, which include electrons, protons, and neutrons– are forbidden from occupying the same ‘quantum states.’ This means that they resist being tightly crammed together.
This theory and the limitation it introduced led Indian-American astrophysicist Subrahmanyan Chandrasekhar to question if there was an upper cap at which this protection against gravitational collapse would fail.
Chandrasekhar –awarded the 1983 Nobel Prize in physics for his work concerning stellar evolution– proposed in 1931 that above 1.4 solar masses, a white dwarf would no longer be protected from gravitational collapse by degeneracy pressure. Past this limit — termed the Chandrasekhar limit — gravity overwhelms the Pauli exclusion principle and gravitational collapse can continue.
But there is another limit that prevents stars of even this greater mass from creating black holes.
Thanks to the 1932 discovery of neutrons— the neutral partner of protons in atomic nuclei — Russian theoretical physicist Lev Landau began to ponder the possible existence of neutron stars. The outer part of these stars would contain neutron-rich nuclei, whilst the inner sections would be formed from a ‘quantum fluid’ comprised of mostly neutrons
These neutron stars would also be protected against gravitational collapse by degeneracy pressure — this time provided by this neutron fluid. In addition to this, the greater mass of the neutron in comparison to the electron would allow neutron stars to reach a greater density before undergoing collapse.
By 1939, Robert Oppenheimer had calculated that the mass-limit for neutron stars would be roughly 3 times the mass of the Sun.
To put this into perspective, a white dwarf with the mass of the Sun would be expected to have a millionth of our star’s volume — giving it a radius of 5000km, roughly that of the Earth. A neutron star of a similar mass though would have a radius of about 20km — roughly the size of a city.
Above the Oppenheimer-Volkoff limit, gravitational collapse begins again. This time no limits exist between this collapse and the creation of the densest possible state in which matter can exist. The state found at the central singularity of a black hole.
We’ve covered the creation of black holes and the hurdles that stand in the way of the formation of such areas of spacetime, but theory isn’t quite ready to hand black holes over to practical observations just yet. The field equations of general relativity can also be useful in the categorisation of black holes.
The four types of black holes
Categorising black holes is actually fairly straight-forward thanks to the fact that they possess very few independent qualities. John Wheeler had a colourful way of describing this lack of characteristics. The physicist once commented that black holes ‘have no hair,’ meaning that outside a few characteristics they are essentially indistinguishable. This comment became immortalised as the no-hair theorem of black holes.
Black holes have only three independent measurable properties — mass, angular momentum and electric charge. All black holes must have mass, so this means there are only four different types of a black hole based on these qualities. Each is defined by the metric or the function used to describe it.
This means that black holes can be quite easily catagorised by the properties they possess as seen below.
This isn’t the most common or most suitable method of categorising black holes, however. As mass is the only property that is common to all black holes, the most straight-forward and natural way of listing them is by their mass. These mass categories are imperfectly defined and so far black holes in some of the categories–most notably intermediate black holes– remain undetected.
Cosmologists believe that the majority of black holes are rotating and non-charged Kerr black holes. And the study of these spacetime events reveals a phenomenon that perfectly exemplifies their power and influence on spacetime.
The Anatomy of a Kerr Black Hole
The mathematics of the Kerr metric used to describe non-charged rotating black holes reveals that as they rotate, the very fabric of spacetime that surrounds them is dragged along in the direction of the rotation.
The powerful phenomenon is known as ‘frame-dragging’ or the Lense-Thirring effect and leads to the violent churning environments that surround Kerr black holes. Recent research has revealed that this frame-dragging could be responsible for the breaking and reconnecting of magnetic field lines that in-turn, launch powerful astrophysical jets into the cosmos.
The static limit of a Kerr black hole also has an interesting physical significance. This is the point at which light–or any particle for that matter– is no-longer free to travel in any direction. Though not a light-trapping surface like the event horizon, the static limit pulls light in the direction of rotation of the black hole. Thus, light can still escape the static limit but only in a specific direction.
British theoretical physicist and 2020 Nobel Laureate Sir Roger Penrose also suggested that the static limit could be responsible for a process that could cause black holes to ‘leak’ energy into the surrounding Universe. Should a particle decay into a particle and its corresponding anti-particle at the edge of the static limit it would be possible for the latter to fall into the black hole, whilst its counterpart is launched into the surrounding Universe.
This has the net effect of reducing the black hole’s mass whilst increasing the mass content of the wider Universe.
We’ve seen what happens to light at the edge of a black hole and explored the fate of particles that fall within a Kerr black hole’s static limit, but what would happen to an astronaut that strayed too close to the edge of such a spacetime event?
Death by Spaghettification
Of course, any astronaut falling into a black hole would be completely crushed upon reaching its central gravitational singularity, but the journey may spell doom even before this point has been reached. This is thanks to the tidal forces generated by the black hole’s immense gravitational influence.
As the astronaut’s centre of mass falls towards the black hole, the object’s effect on spacetime around it causes their head and feet to arrive at significantly different times. The difference in the gravitational force at the astronaut’s head and feet gives rise to such a huge tidal force that means their body would be simultaneously compressed at the sides and stretched out.
Physicists refer to this process as spaghettification. A witty name for a pretty horrible way to die. Fortunately, we haven’t yet lost any astronauts to this bizarre demise, but astronomers have been able to watch stars meet the same fate.
For a stellar-mass black hole, spaghettification would occur not just before our astronaut reaches the central singularity, but also well before they even hit the event horizon. For a black hole 40 times the mass of our Sun — spaghettification would occur at about 1,000 km out from the event horizon, which is, itself, 120 km from the central gravitational singularity.
As well as developing the Oppenheimer-Volkoff limit, Oppenheimer also used general relativity to describe how a total gravitational collapse should appear to a distant observer. They would consider the collapse to take an infinitely long time, the process appearing to slow and freeze as the star’s surface shrinks towards the Schwarzschild radius.
An astronaut falling into a black hole would be immortalized in a similar way to a distant observer, though they themselves–could they have survived spaghettification– they would notice nothing. The passing of Rs would just seem a natural part of the fall to them despite it marking the point of no return.
Much More to Learn…
After emerging from the mathematics of general relativity at the earlier stages of the 20th Century, black holes have developed from a theoretical curiosity to the status of scientific reality. In the process, they have indelibly worked their way into our culture and lexicon.
Perhaps the most exciting thing about black holes is that there is so much we don’t yet know about them. As a striking example of that, almost all the information listed above resulted just from theory and the interrogation of the maths of Einstein’s field equations.
Unlocking the secrets held by black holes could, in turn, reveal how galaxies evolve and how the Universe itself has changed since its early epochs.
Sources and Further Reading
Relativity, Gravitation and Cosmology, Robert J. Lambourne, Cambridge Press, .
Relativity, Gravitation and Cosmology: A basic introduction, Ta-Pei Cheng, Oxford University Press, .
As an interstellar visitor–an object from outside the solar system–the rogue comet 2I/Borisov is already a source of great interest for astronomers. But researchers have now also discovered that this interstellar comet is composed of pristine material similar to that which exists when star systems first form.
Not only does this make 2I/Borisov even more exciting than previously believed, it means that studying the material that composes it and its coma –an envelope of gas and dust that surround comets– could unlock secrets of planetary system formation.
“2I/Borisov could represent the first truly pristine comet ever observed,” says Stefano Bagnulo of the Armagh Observatory and Planetarium, Northern Ireland, UK. The astronomer tells ZME Science: “We presume this is because it has travelled in the interstellar medium without interacting with any other stars before reaching the Sun.”
Bagnulo is the lead author of one of two papers published in the Nature family of journals detailing new in-depth analysis of 2I/Borisov.
Reflecting on 2I/Borisov
The team was able to make its detailed study of 2I/Borisov–the second interstellar comet found trespassing in our solar system after the cigar-shaped Oumuamua–using the Very Large Telescope (VLT) located in the Acatma Desert, Northern Chile.
In particular, they employed the FOcal Reducer and low dispersion Spectrograph (FORS2) instrument–a device capable of taking mages of relatively large areas of the sky with very high sensitivity–and a technique called polarimetry to unlock the comet’s secrets.
“Sunlight scattered by material, for instance, reflected by a surface, is partially polarised,” explains Bagnulo comparing this to polaroid sunglasses which absorb the polarised component of the light and thus dampen reflected light suppressing glare. “In astronomy, we are interested in that polarised radiation because it carries information about the structure and composition of the reflecting surface or scattering material.”
Bagnulo continues by explaining that because light reflected by a darker object is polarised more than the light reflected by a brighter object, polarimetry may be used to estimate the albedo of an asteroid. This makes it a tool regularly used to study comets and allowed the team to compare 2I/Borisov to comets that begin life in our solar system.
“We found that the polarimetric behaviour of 2I/Borisov is different than that of all other comets of our solar system, except for one, Comet Hale-Bopp,” Bagnulo says. “We suggest that this is because Hale-Bopp is a pristine comet.”
It also implies that 2I/Borisov and Halle-Bopp formed in similar environments, thus giving us a good picture of conditions in other planetary systems.
Whilst, Bagnulo and his team were conducting this research with data collected by the VLT, another team was using a different method to examine the material that comprises this interstellar comet.
The Secrets in the Dust of 2I/Borisov
Bin Yang, is an astronomer at ESO in Chile, who also took advantage of 2I/Borisov’s intrusion into the solar system to study this mysterious comet, but using the Atacama Large Millimeter/submillimeter Array (ALMA).
“I had the idea of observing the thermal emission from the dust particles in the coma of 2I/Borisov using ALMA. My co-author Aigen Li constructed theoretical models to fit the ALMA observation and set constraints on the dust properties,” Yang, the lead author of the second paper detailing the 2I/Borisov investigation, tells ZME Science. “The composition of 2I/Borisov is similar to solar system comets, consists of dust and various ices. The major ices are water ice, carbon monoxide ice and the minor species include hydrogen cyanide and ammonia.”
Yang goes on to explain that the team was not able to precisely determine the composition of 2I/Borisov’s dust component. The astronomer adds that it could be composed of silicates or carbonaceous materials or a mixture of both.
The team also found that the comet’s coma contains compact pebbles and grains of around 1mm and above.
Additionally, as 2I/Borisov neared the Sun the relative amounts of water and carbon they detected from it changed quite drastically.
“We found that the dust coma of Borisov consists of compact, millimeter-sized and larger pebble-like grains, which formed in the inner region near the central star,” Yang says. “We also found the cometary nucleus consists of components formed at different locations in its home system.”
“Our observations suggest that Borisov’s system exchanged materials between the inner regions and the outer regions that are far from the central star, perhaps due to gravitational stirring by giant planets much like in our own solar system.”
Bin Yang, ESO.
These characteristics indicate that 2I/Borisov formed by collecting materials from different locations in its own planetary system. It also imnplies that the system from which it originated likelty featured the exchange of materials between its inner and outer regions. Something that Yang says is also common in our solar system.
“So, it is possible that chaotic material exchanging processes are common phenomena for young planetary systems,” says Yang. “We want to know if other planetary systems form like our own. But we cannot study these systems to the level of their individual comets.”
“Interstellar objects represent the building blocks of planets around other stars. Comet Borisov provides a rare and valuable link between our own solar system and other planetary systems.”
The Journey of 2I/Borisov
2I/Borisov was first discovered by Gennedy Borisov, an amateur astronomer and telescope maker, in August 2019. It was only the second visitor from outside the solar system to be found within our planetary system. That means that as it passed the Sun it presented a unique opportunity to compare conditions in our small corner of the galaxy to those found in other planetary systems.
“2I/Borisov is quite a small comet and it didn’t get very close to the Earth and the Sun, so the emission from this comet is quite weak. We were happily surprised that we actually detected the thermal emission from this alien comet. Because of this detection, we are able to set constraints on the dust properties of this comet,” says Yang. “Comets in other planetary systems are simply too far away and too small to be seen by our telescopes.
“We are extremely lucky to find a comet that is from a planetary system far far away from us. Even more luckily, we managed to take many pictures and spectra of this alien comet during its short visit.”
Bin Yang, ESO.
As Yang points out, 2I/Borisov is only in our solar system for a short time before it must continue its interstellar journey, so the time available to astronomers to study it is limited. But, with interstellar visitors to the solar system believed to be fairly common, but difficult to spot, improving telescope technology could offer future opportunities to study other objects with similar interstellar origins.
Bagnulo points to both the upcoming Vera C Rubin telescope and ESA’s comet interceptor, set to launch in 2029, as future technology that could help us spot and investigate interstellar comets.
“We expect to detect at least one interstellar object per year,” Yang concludes. “So, we will have more opportunities to study alien materials.”
Using the Event Horizon Telescope (EHT) to observe the supermassive black hole at the centre of the galaxy Messier 87 (M87), astronomers have once again produced another first in the field of astronomy and cosmology.
Following up on the image of M87’s black hole published two years ago–the first time a black hole was imaged directly–astronomers at the EHT collaboration have captured a stunning image of the same black hole, this time in polarized light.
The achievement marks more than just an impressively sharp and clear second image of this black hole however–it also represents that first-time researchers have been able to capture the polarization of light around such an object.
Not only does this reveal details of the magnetic field that surrounds the supermassive black hole, but it also could give cosmologists the key to explaining how energetic jets launch from the core of this distant galaxy.
“M87 is a truly special object! It is tied for the largest black hole in the sky with the black hole in our galaxy–Sagittarius A*, ” Geoffrey C. Bower, EHT Project Scientist and assistant research astronomer at the Academia Sinica Institute of Astronomy and Astrophysics, tells ZME Science. “It’s about one thousand times further away but also one thousand times more massive.
“The M87 black hole’s home is in the centre of the Virgo Cluster, the nearest massive cluster of galaxies, each with its own black hole. This makes it a great laboratory for studying the growth of galaxies and black holes.”
Geoffrey C. Bower, Academia Sinica Institute of Astronomy and Astrophysics.
Along with Monika Mościbrodzka, Coordinator of the EHT Polarimetry Working Group and Assistant Professor at Radboud University, Netherlands, Bower is one of the authors on two papers detailing the breakthrough published in the latest edition of The Astrophysical Journal Letters.
“We are now seeing the next crucial piece of evidence to understand how magnetic fields behave around black holes, and how activity in this very compact region of space can drive powerful jets that extend far beyond the galaxy,” says Mościbrodzka.
“We have never see magnetic fields directly so close to the event horizon,” the astronomer tells ZME Science.
“We now, for the first time, have information on how magnetic field lines are oriented close to the event horizon and how strong these magnetic fields are. All this information is new.”
Deeper Into the Heart of M87
The release of the first image of a black hole on the 10th of April 2019 marked a milestone event in science, and ever since then, the team behind that image has worked hard to delve deeper into M87’s black hole. This second image is the culmination of this quest. The observation of the polarized light allows us to better understand the information in that prior image and the physics of black holes.
“Light is an electromagnetic wave which has amplitude and direction of oscillation or polarization,” explains Mościbrodzka. “With the EHT we observed that light in the M87’s surrounding ring is polarized meaning that waves oscillation have a preferred direction.”
This polarization is a property of synchrotron radiation that is produced in the vicinity of this black hole. Polarization occurs when light passes through a filter–think of polarized sunglasses blocking out light and thus giving you a clearer view–thus the polarization of light in this picture accounts for this clearer view of M87’s black hole, which reveals a great deal of information about the black hole itself.
“The polarization of the synchrotron light tells us about the orientation of magnetic fields. So by measuring light polarization we can map out the magnetic fields around the black hole.”
Monika Mościbrodzka, Coordinator of the EHT Polarimetry Working Group and Assistant Professor, Radboud University
Capturing such an image of polarized light at a distance of 55 million light-years is no mean feat, and is only possible with the eight linked telescopes across the globe that comprise the EHT. Together these telescopes–including the 66 antennas of the Atacama Large Millimeter/submillimeter Array (ALMA)–form a virtual telescope that is as large as the Earth itself with a resolution equivalent to reading a business card on the Moon.
“As a virtual telescope that is effectively as large as our planet the EHT has a resolution power than no other telescope has,” says Mościbrodzka. “The EHT is observing the edge of what is known to humans, the edge of space and time. And for the second time, it has allowed us to bring to the public the images of this black hole.”
This image–as the above comparison shows– has had its clarity enhanced immensely by calibration with data provided by the Atacama Pathfinder EXperiment (APEX).
Of course, these magnetic fields are responsible for much more than just giving us a crystal clear image of the black hole they surround. They also govern many of the physical processes that make black holes such powerful and fascinating events–including one of M87’s most mysterious features.
How Magnetic Fields Help Black Holes ‘Feed’
The M87 galaxy–55 million light years from Earth– is notable for its powerful astrophysical jets that blast out of its core and extend for 5000 light-years. Researchers believe that these jets are caused when some of the matter at the edge of the black hole escapes consumption.
Whilst other matter falls to the surface of the central black hole and disappears to the central singularity, this escaping matter is launched into space as these remarkable jets.
Even though this is a more than plausible explanation, many questions still remain about the process, namely, how an area that is no bigger than our solar system creates jets that are greater in length than the entire galaxy that surrounds it.
This image of the polarized light around M87’s black hole which offers a glimpse into this inner region finally gives scientists a chance to answer these mysteries.
“Our planet’s magnetosphere prevents ionized particles emitted by the Sun from reaching the Earth’s surface. In the same way, strong black hole magnetic fields can prevent or slow down the accretion of matter onto the black hole,” Bowers says. “Those strong magnetic fields are also powerful for generating the jets of particles that flow at near the speed of light away from the black hole.”
By mitigating the feeding process of their central black holes, however, these magnetic fields may have an influence that like the jets they create may extend even further than M87 itself. They could be affecting the entire galactic cluster.
“Magnetic fields can play a very important role in how black holes ‘eat.’ If the fields are strong enough, they can prevent inflowing material from reaching the black hole. They are also important in funnelling matter out into the relativistic jets that burst from the black hole region. These jets are so powerful that they influence gas dynamics amongst the entire cluster of galaxies surrounding M87.”
Geoffrey C. Bower, Academia Sinica Institute of Astronomy and Astrophysics.
This means a better understanding of the magnetic fields around M87’s black hole also gives researchers an improved understanding of how the matter behaves at the edge of that black hole and perhaps of how such things affect neighbouring galaxies and their evolution.
And from the image of M87’s black hole the EHT team have developed, it looks clear that of the various models that cosmologists have developed to describe the interaction of matter at the edge of black holes, only those featuring strongly magnetized gases can account for its observed features.
“We have now a better idea about the physical process in the ring visible in the image,” Mościbrodzka says. “We now know more precisely how strong magnetic fields can be near a black hole. We also know more accurately at what rate the black hole is swallowing matter. And we have a better idea of what the black hole might look like in the future.”
In terms of what is next for black hole imaging, both Mościbrodzka and Bowers are clear; they have their sights set on a black hole that is closer to home than M87–the one that sits at the centre of the Milky Way, which despite being closer to home, could be a tougher nut to crack in terms of imaging.
“We’re hard at work on a problem that we know everyone wants to see; an image of the black hole at the centre of our galaxy,” says Bowers. “This is really tricky because the gas around the black hole moves so fast that the image may be changing on same the time scale that it takes to snap our picture. We think we know how to handle this problem but it requires a lot of technical innovation.”
Given the advancements already made by the EHT collaboration team, it would be unwise to bet against them achieving this lofty goal at some point in the not too distant future.
“We’ve gone from imagining what happens around black holes to actually imaging it!” Bowers concludes. “In the near future, we’ll be able to show a movie of material orbiting the black hole and getting ejected into a jet. I never thought I would see anything like this.
“Black holes are the simplest but most enigmatic objects in the Universe. These observations are just the beginning of the road to understanding them.”
Geoffrey C. Bower, Academia Sinica Institute of Astronomy and Astrophysics.
Using the aftermath of a comet collision in 1994 astronomers have measured the winds blowing across Jupiter‘s stratosphere for the first time. The team has discovered that these winds raging around the middle atmosphere of the solar system’s largest planet are incredibly powerful–reaching speeds of up to 400 metres per second at the poles.
The team’s findings represent a significant breakthrough in planetary metrology and mark the gas giant out as what the team are describing as a ‘unique metrological beast in the solar system.’
To conduct the research the astronomers diverged from the usual methods used to measure the winds of Jupiter. Previous attempts to measure the gas giant’s winds have hinged on measuring swirling clouds of gas–seen as the planet’s distinctive red and white bands–but this method is only effective in measuring winds in the lower atmosphere. Whereas, by using aurorae at Jupiter’s poles researchers have been able to model winds in the upper atmosphere. But, both of these methods, even when used in conjunction, have left the winds in the middle section of the gas giant’s atmosphere–the stratosphere– something of a mystery.
That is until now. This team of astronomers used the Atacama Large Millimetre Array (ALMA) to track molecules left in Jupiter’s atmosphere by the collision with the comet Shoemaker-Levy 9 in 1994.
“We had to use ALMA’s ability to quickly map Jupiter’s spectral emission at very high spatial and spectral resolution in the submillimeter and observe the Doppler shifts induced by the winds on the spectral line we targeted,” team leader Thibault Cavalié, Laboratoire d’Astrophysique de Bordeaux, France, exclusively tells ZME Science. “We could deduce the wind speeds just like you could deduce the speed of a passing fire engine by the change in frequency of its siren. This spectral line is formed in the stratosphere, giving us access to the winds at this altitude.
“It is the first time we achieve measuring directly winds in the stratosphere of Jupiter, which lacks visual tracers such as clouds.”
Thibault Cavalié, Laboratoire d’Astrophysique de Bordeaux, France.
Cavalié explains that the team had to use ALMA’s ability to quickly map Jupiter’s spectral emission at very high spatial and spectral resolution in the submillimeter and observe the Doppler shifts induced by the winds on the spectral line they targeted.
“We could deduce the wind speeds just like you could deduce the speed of a passing fire engine by the change in frequency of its siren,” the researcher continues. “This spectral line is formed in the stratosphere, giving us access to the winds at this altitude.”
What the astronomers discovered was powerful winds in the middle atmosphere of Jupiter in two different locations. One set of winds conformed to expectations, but the other came as a surprise.
Jupiter’s ‘Supersonic Jet’ Winds
Cavalié explains that the team first found a 200 metres per second eastward jet just north of the equator in ‘super-rotation–meaning that the wind rotates faster around the planet than the planet rotates itself. “Winds at such latitudes were expected from models and previous temperature measurements at these low latitudes,” the astronomer adds.
But, not everything observed by the team conformed to expectations.
“Most surprisingly, we identified winds located under the main UV auroral emission near Jupiter’s poles. These winds have velocities of 300 to 400 meters per second,” Cavalié says. “While the equatorial winds were kind of anticipated, the auroral winds and their high speed were absolutely unexpected.”
To put this into perspective, the fastest winds ever recorded on earth reached a speed of just 103 metres per second–measured at the Mount Washington Observatory in 1931. These auroral winds even beat the winds recorded in Jupiter’s Great Red Spot–an ongoing raging storm on the surface of the gas giant–which have been clocked at around 120 metres per second.
The speed of these jets isn’t their only intimidating quality, however. The jets seem to behave like a giant vortex with a diameter around four times that of our entire planet, reaching a height of around 900 kilometres.
“A vortex of this size would be a unique meteorological beast in our Solar System.”
Thibault Cavalié, Laboratoire d’Astrophysique de Bordeaux, France.
The team’s measurements and stunning discovery, documented in a paper published in the latest edition of Astronomy & Astrophysics, wouldn’t have been possible without a violent incident in Jupiter’s recent history.
Shoemaker-Levy 9 Still has Impact
The impact of Shoemaker-Levy 9 upon the surface of Jupiter was an event–or more precisely a series of events– that had already made history before its effects made this research possible.
The comet broke up in the planet’s atmosphere resulting in a series of impacts that had never been studied prior to 1994, and its somewhat ironic that thanks to this study, Shoemaker-Levy 9 is still having an impact today. The comet left traces of hydrogen cyanide swirling in Jupiter’s atmosphere which the team was able to track.
“The team measured the Doppler shift of hydrogen cyanide molecules — tiny changes in the frequency of radiation emitted by the molecules — caused by their motion driven by stratospheric winds on Jupiter,” says Thomas K Greathouse, Senior Research Scientist at Southwest Research Institute (SwRI), responsible for the development of the study and analysis of the observational results. “
“The high spectral and spatial resolution and the exquisite sensitivity of the observations at the wavelengths covered by ALMA allowed us to map such small Doppler shifts caused by the winds in the stratosphere all along the limb of Jupiter.”
Thomas K Greathouse, Senior Research Scientist at Southwest Research Institute (SwRI).
The fact that the team was able to obtain all the measurements they did with just 30 minutes of operating time with ALMA is a striking testament to the power and precision of the 66 antennas that make up the telescope array located in the Atacama Desert of Nothern Chile, currently the most powerful radio telescope on Earth.
“It was the availability of ALMA that made these measurements possible. Previous radio observatory facilities did not have the combination of spectral and spatial resolution along with the high sensitivity needed to measure the winds as was done in this study,” Greathouse tells ZME Science. “Making further observations using ALMA to capture Jupiter at different orientations will allow us to study these winds in more detail and allow us to look for temporal variability in them as well.
“Additionally, more extensive measurements will be possible from the JUICE mission and its Submillimetre Wave Instrument slated for launch in 2022.”
The Future of Jupiter Investigations
JUICE or JUpiter ICy moons Explorer is the first large-class mission in the European Space Agency’s (ESA) Cosmic Vision program and will arrive at Jupiter in 2029 when it will begin a three-year mission observing the gas giant in intense detail.
“This is why science is so much fun. We have worked hard to understand a system–Jupiter’s stratosphere in this case–as best we can, we make our predictions about something–stratospheric wind behaviour–and then go test those predictions. If we are right, fantastic, we move on to the next problem, but if we are wrong we have learned something new and unique and can then continue making further studies to come to a more complete understanding of the system.”
Thomas K Greathouse, Senior Research Scientist at Southwest Research Institute (SwRI).
For Cavalié, who has been involved with the measurement of Jupiter’s winds since 2009, the future is bright for such investigations and what they can tell us about the solar system’s largest planet and gas giants in general. “We now want to use ALMA again to characterize the temporal variability of the equatorial winds,” the astronomer says. “It is expected from temperature measurements and models that the direction of the equatorial winds should oscillate from eastward to westward with a period of about 4 years.”
The scientist is also clear, just because he and his colleagues have achieved a first, that doesn’t mean they are prepared to rest on their laurels. There are a lot of exciting developments on the way, and thus a lot of work to be done.
“We also want to observe the auroral winds during a Juno perijove pass to compare our data with observations of the poles by the spacecraft to better understand their origin and what maintains them,” he explains. “In addition, this study is a stepping stone for future investigations to be conducted using the same technique with JUICE and its Submillitre Wave Instrument.”
In addition to these missions, the ESO’s Extremely Large Telescope (ELT)–due to start operations later this decade–will also join investigations of Jupiter and should be capable of providing highly detailed investigations of the gas giant’s atmosphere.
“Jupiter and the giant planets are fascinating worlds. Understanding how these planets formed and how they work is a source of daily motivation, especially when working with world-class observatories like ALMA and participating in space missions to explore Jupiter and its satellites.”
Thibault Cavalié, Laboratoire d’Astrophysique de Bordeaux, France.
Using the Hubble Space Telescope astronomers have spotted an important and extraordinary event in planetary evolution for the first time. The researchers have observed volcanic activity on a distant rocky planet reforming that world’s atmosphere.
The planet–GJ 1132 b–is believed by the team to have previously possessed an atmosphere that was stripped by the intense radiation emitted by the bright young red dwarf star it closely orbits. After its thick blanket of hydrogen and helium was expunged the planet was left as a rocky core roughly the size of Earth.
The astronomers believe that much of the hydrogen from GJ 1132 b’s initial atmosphere was absorbed by the exoplanet’s molten magma mantle creating a reservoir of the element which is now being slowly dispersed back into the atmosphere. This dispersal replenishes hydrogen being lost to space.
The fact that the planet’s volcanic activity is generating a secondary atmosphere that is replacing the first has come as a huge suprise to the researchers.
What makes this replacement atmosphere so interesting and useful to astronomers is the fact that has come from the planet’s interior. Thus its chemical composition–with abundant hydrogen, hydrogen cyanide, methane and ammonia with glimmers of a hydrocarbons–means that astronomers should be able to study the interior of the exoplanet by proxy.
“This second atmosphere comes from the surface and interior of the planet, and so it is a window onto the geology of another world,” explains Paul Rimmer, University of Cambridge, UK, who was part of the team that made the discovery. “A lot more work needs to be done to properly look through it, but the discovery of this window is of great importance.”
The finding could change the way we think about highly irradiated exoplanets which astronomers normally expect to lack atmospheres. “We first thought that these highly radiated planets would be pretty boring because we believed that they lost their atmospheres,” explains Raissa Estrela of the Jet Propulsion Laboratory at the California Institute of Technology in Pasadena, California, USA, another member of the research team. “But we looked at existing observations of this planet with Hubble and realised that there is an atmosphere there.”
Like Earth, But Really Different
Whilst sharing some similarities with Earth, GJ 1132 b is actually a very different world. GJ 1132 b has a similar density, size and age–around 4.5 billion years. Additionally, both planets started life as molten balls of rock with hydrogen-dominated atmospheres. But, whereas our planet was able to hang on to its atmosphere, the intense radiation GJ 1132 b was exposed to stripped that world’s gaseous envelope.
The differences become more extreme when considering the formation of both worlds. GJ 1132 b is the surviving core of a sub-Neptune exoplanet–a planet resembling Neptune but with a smaller mass–so didn’t start its life as a terrestrial world like we believe Earth did. Possibly the most extreme difference between the two worlds, however, is their relationships with their respective parent stars.
Whilst Earth orbits the Sun at a comfortable distance, rotating on its axis as it does so, GJ 1132 b orbits its red dwarf parent star in blisteringly close proximity. So-close that the exoplanet’s orbit period is just 36 hours. That isn’t the only major orbital difference, however. GJ 1132 b is tidally locked, meaning that the same face points towards its parent star throughout its orbit.
This isn’t the only source of heating the exoplanet is experiencing. The tidal force that the planet experiences due to its proximity to its parent star and that star’s gravitational force is permanently stretching and squeezing it.
This deformation is converted to heat beneath the planet’s surface, maintaining its mantle’s molten state. It could be this tidal heating that is driving the extreme volcanism and also causing the planet’s thin crust to crack, allowing hydron to escape and replenish the atmosphere.
The findings raise the question; how many of the terrestrial worlds we see are actually the stripped cores of sub-Neptunes?
“How many terrestrial planets don’t begin as terrestrials? Some may start as sub-Neptunes, and they become terrestrials through a mechanism whereby light evaporates the primordial atmosphere,” says Mark Swain of NASA’s Jet Propulsion Laboratory who led the research. “This process works early in a planet’s life when the star is hotter. Then the star cools down and the planet’s just sitting there.”
“So you’ve got this mechanism that can cook off the atmosphere in the first 100 million years, and then things settle down. And if you can regenerate the atmosphere, maybe you can keep it.”
The observations made by the team were part of the Hubble observing program and raise the interesting possibility that if this secondary atmosphere is thin enough, astronomers could actually see down to the surface of the exoplanet.
“This result is significant because it gives exoplanet scientists a way to figure out something about a planet’s geology from its atmosphere,” concludes Rimmer. “It is also important for understanding where the rocky planets in our own Solar System — Mercury, Venus, Earth and Mars, fit into the bigger picture of comparative planetology, in terms of the availability of hydrogen versus oxygen in the atmosphere.”
With assistance from the ESO’s Very Large Telescope (VLT), astronomers have discovered the most distant radio emission ever recorded. The source is a quasar so distant that its light has been travelling 13 billion years to reach us. That means that it existed when the Universe was just 780 or so million years old.
The object–named P172+18–is what astronomers term a ‘radio loud’ quasar, shining powerfully in the radio-frequency region of the electromagnetic spectrum, extremely bright due to the powerful jets emitted from its axis. Radio loud quasars are fairly rare with only 10% of discovered quasars fitting this description.
This makes the team’s finding even more extraordinary as even though more distant quasars have been found, it marks the first time that researchers have been able to identify the tell-tale signs of powerful radio-bright jets at such incredible cosmic distances.
Excitingly, the team at the centre of this finding believe that this is just the tip of the iceberg with regards to radio-loud quasars, with many more yet to be discovered. Possibly even some at much greater distances.
The team’s discovery is discussed in a paper published in the latest edition of The Astrophysical Journal.
Quasars: Powered By Black Holes
Quasars are objects that lie at the centre of galaxies, powered by supermassive black hole ‘engines.’ The black hole at the heart of P172+18 is a doozy. The team estimate it is around 300 million times the mass of the Sun. As impressive as that is, perhaps more staggering is the rate at which this supermassive black hole is consuming gas and dust.
“The black hole is eating up matter very rapidly, growing in mass at one of the highest rates ever observed,” says Chiara Mazzucchelli, co-leader of the project and an astronomer based at ESO, Chile. “I find it very exciting to discover ‘new’ black holes for the first time, and to provide one more building block to understand the primordial Universe, where we come from, and ultimately ourselves.”
The team believes that the rapid rate of gas consumption displayed by the supermassive black hole and its burgeoning growth are both intrinsically linked to the emission of the radio bright jets they detected. The jets could be disturbing gas in an accretion disc around the black hole, causing it to fall into the central black hole at an accelerated rate.
If this proves to be the case, the study of radio-loud quasars could be of vital importance in the future investigation of the growth of black holes in the infant Universe. There is currently some confusion as to how supermassive black holes could have grown to tremendous sizes over a relatively short-period in cosmic terms, thus a mechanism that accounts for rapid growth is a boon to cosmologists fearing that models of cosmic evolution could need fundamental revision.
Very Loud and Very Far Away
P172+18 was first spotted as a radio source in data gathered by t the Magellan Telescope at Las Campanas Observatory in Chile. Mazzucchelli and team co-leader Eduardo Bañados of the Max Planck Institute for Astronomy, Germany, then assessed the data and quickly concluded that the radio source represented jets produced by a distant radio-loud quasar.
“As soon as we got the data, we inspected it by eye, and we knew immediately that we had discovered the most distant radio-loud quasar known so far,” says Bañados.
Because P172+18 was only observed for a brief period, it was necessary for the duo to follow up the observations with other telescopes. They were able to do this with the use of the X-Shooter instrument associated with the VLT, based in the Atacama Desert, Chile, as well as the National Radio Astronomy Observatory’s Very Large Array (VLA) in New Mexico, and the Keck Telescope located near the summit of Mauna Kea, Hawaii.
These follow-up observations allowed the team to ascertain a wealth of details about the quasar and the supermassive black hole powering it, including its mass and the rapid rate at which it is consuming gas and surrounding matter.
P172+18 may currently hold the record for most distant radio-loud quasar, but it is not a distinction that Mazzucchelli and Bañados think it will hang on to for long. The duo believes that many more radio-loud quasars are lurking in the Universe waiting to be discovered and that undoubtedly, some of these will exist at greater distances than 13 billion light-years.
Whilst these may be a challenge to spot currently, the ESO’s forthcoming Extremely Large Telescope (ELT), currently under construction in Northern Chile, should be powerful enough to handle such observations.
“This discovery makes me optimistic and I believe — and hope — that the distance record will be broken soon,” concludes Bañados.
An international team of astronomers has discovered a nearby exoplanet orbiting a red dwarf star that is perfect for deeper investigation. In particular, this exoplanet could be a prime target for precise atmospheric measurements, something that, for planets outside the solar system, has so-far eluded astronomers.
The team’s findings documenting the discovery of this relatively close super-Earth–so-called because they have a mass greater than our planet but still lower than planets like Uranus and Neptune which are classified as ‘ice giants’–are published in the latest edition of the journal Science.
The team discovered Gliese 486 b whilst surveying 350 small red dwarf stars for signs of low-mass planets using the CARMENES spectrograph mounted on the 3.5m telescope at the Calar Alto Observatory telescope, Spain. The exoplanet was found due to the ‘wobble’ it caused in the orbit of its parent star.
“Our team is searching primarily for Earth-like and super-Earth planets orbiting nearby stars. In this case, we have found a nearby super-Earth, just 26 light-years away orbiting a small star every 1.5 or so Earth days,” Karen Collins, an astronomer at the Center for Astrophysics, Harvard & Smithsonian, and a co-author on the paper tells ZME Science. “We were certainly excited to have found a transit signal in the light curve of a star that is so close to the Sun in astronomical terms.
“We quickly realized that Gliese 486 b, with radial velocity mass measurements in hand, would likely become a prime target for additional detailed follow-up studies, particularly atmospheric investigations.”
Karen Collins, Center for Astrophysics, Harvard & Smithsonian
These investigations could include searching for the conditions necessary for life, or even for biomarkers left behind by simple lifeforms.
Colins continues by explaining that it is Gliese 486 b’s proximity–it is the third closest transiting exoplanet yet to be uncovered– that, amongst other things like its temperature, makes it a good candidate for more in-depth study. “Because Gliese 486 b is so close to the solar system, relative to most known transiting exoplanets, we may be able to probe the atmosphere of the planet using the upcoming James Webb Space Telescope and possibly other telescopes,” she explains.
That is, of course, if it actually has an atmosphere.
What We Know About Gliese 486 b So Far…
Whilst the team of astronomers may not yet be certain that Gliese 486 b has an atmosphere, there are some things that they do know about the exoplanet and its red dwarf home star.
“It is only about 30% larger than Earth but has a mass of about 2.8 times that of our planet,” study author Trifon Trifonov, Max Planck Institute for Astronomy, explains to ZME Science. The researcher adds that models suggest that the exoplanet’s composition is similar to Venus and Earth, including a metallic core. “Anyone standing on Gliese 486 b would feel a gravitational pull that is about 70% stronger than what we experience on Earth.”
In addition to being denser than the earth, Gliese 486 b is also much hotter according to Trifon. This is because the exoplanet revolves around its host star on a circular orbit every 1.47 days, with one side permanently pointing towards its parent star.
“The proximity to the red dwarf Gliese 486 heats the planet significantly, making its landscape hot and dry, interspersed with volcanos and glowing lava rivers,” Trifon says. “There are quite a few super-Earth type exoplanets already discovered. All of these exoplanets are exceptional on their own. In this context, the physical characteristics of Gliese 486 b are not uncommon. However, the proximity of Gliese 486 b, allowed us to measure its mass with unprecedented precision, thanks to observations done with the CARMENES and the MAROON-X instruments.”
From the information the astronomers do possess regarding Gliese 486 b, especially its mass, Collins adds that the clues it also has an appreciable atmosphere are in place.
“Because we do know that the planet surface gravity is relatively high–about 70% stronger than Earth–we believe that there is a chance the planet may have retained an appreciable atmosphere.”
Karen Collins, Center for Astrophysics, Harvard & Smithsonian
Using NASA’s Transiting Exoplanet Survey Satellite (TESS) spacecraft the astronomers were able to deduce that Gliese 486 b periodically crosses the stellar disk of its parent red dwarf star, a rare and fortuitous event.
“For transiting planets like Gliese 486 b, we have two primary methods to probe the atmospheres, if they exist,” Collins continues. “Transit spectroscopy allows us to study the planet’s atmosphere as the planet passes in front of the star from the telescope’s perspective.”
Collins says that should the exoplanet possess an atmosphere part of the light from its parent star that reaches our telescopes will have been filtered through this. This means that the light profile filtered by the atmosphere can be compared to an unfiltered version when the planet is not in front of the star.”By comparing the in-transit spectrum of the star with a spectrum of the star when the planet is not transiting, we can isolate atmospheric signals from the planet and possibly detect some of the components of the atmosphere.”
The second method detailed by Collins involves the detection of radiation directly from an exoplanet’s hot surface as it occupies different orbital phases across the star’s face. The emission spectrum that gives this technique its name–emission spectroscopy–reveals characteristic traits that indicate the presence of certain elements emitting and absorbing light in the exoplanet’s atmosphere.
“Its temperature of around 700 Kelvin makes it suitable for emission spectroscopy and phase curve studies in search of an atmosphere,” adds Trifonov.
The Golden Age of Exoplanet Science
Concluding our interview I ask Collins and Trionov if we are entering a ‘Golden Age’ for exoplanet science. They are both quick to correct me. “I would say we are living in it!” Trinov exclaims. “During the past three decades, astronomers have discovered thousands of exoplanets, and the number is increasing daily.
“Every day, we enhance our knowledge about the physical properties of exoplanets, their formation, and evolution.”
Trifon Trifonov, Max Planck Institute for Astronomy
Collins is equally assured that exoplanet science is in its prime, but adds that there is no decline in sight. “Frankly, I believe we have been in the golden age of exoplanet science for over a decade now,” the astronomer says. “Even so, with the advent of TESS to discover and measure the size of nearby small transiting planets, precise radial velocity machines like that of the CARMENES consortium and the MAROON-X instrument to measure their masses, and soon the James Webb Space Telescope to investigate their atmospheres, it’s fair to say that we are entering the golden age of well-characterized small planet exoplanet science.”
And Collins is clear how lucky she regards herself for just being involved with astronomy at this crucial juncture in its history. “I am excited to be involved in the search for and characterization of Earth-sized and Super-Earth planets such as Gliese 486 b,” says explains enthusiastically. “Precise atmospheric measurements are likely around the corner! What will this relatively new scientist from a small but progressive astrophysics program at a school in Kentucky be involved with next? Will we soon discover an Earth twin with an Earth-like atmosphere or even signs of life in an atmosphere?
“It is almost as if I’m living in a series of Star Trek. I can’t wait to see what we discover next!”
Karen Collins, Center for Astrophysics, Harvard & Smithsonian
Astronomers have used the Very Long Baseline Array (VLBA) to discover that the first black hole ever detected is actually much larger than previously believed. So large, at 21 times the mass of the Sun, that it challenges existing theories about the evolution of stars and how they form black holes. These constraints should limit stellar black holes in binary systems to about 15 solar masses.
Cygnus X-1 is a Milky Way binary system that contains a black hole and a supergiant companion star feeding it gas and other material. First discovered in 1964, the binary system has gone on to become one of the most intensely studied objects in astronomy. Yet, our familiarity with Cygnus X-1 doesn’t mean it can’t still deliver a surprise or two.
In addition to finding the black hole is 50% more massive than prior estimates, near 21 solar masses as opposed to 15 solar masses, the team also discovered that the companion star also has a greater mass than previous measurements had revealed. The system as a whole is 20% further away than previously calculated–7,200 light-years from Earth as opposed to 6,100 light-years.
“We know that Cygnus X-1 hosts a black hole that is 21 times the mass of the Sun. We also learned that the supergiant companion star in Cygnus X-1 is also more massive than we had thought, with a mass of about 40 times the mass of the Sun,” Professor James Miller-Jones, the International Centre for Radio Astronomy Research (ICRAR), Curtin University, Australia, tells ZME Science. “The revised masses and distances also lead to an updated orbital separation between the star and the black hole — they orbit each other at a separation of one-quarter the distance from the Earth to the Sun.”
The finding, published in the latest edition of the journal Science, means that Cygnus X-1 contains the largest black hole created through the collapse of a star alone, that has ever been detected with traditional electromagnetic astronomy without the use of gravitational waves. Larger black holes do of course exist, but these are formed through other mechanisms such as mergers between smaller black holes after that initial stellar collapse.
Miller-Jones, the study’s lead researcher, goes on to explain that the team also learned that the black hole is spinning very rapidly , close to its maximum possible speed.
“With all this new information, we were able to propose a likely scenario for how this system formed, which can explain its observed properties.”
Professor James Miller-Jones, ICRAR, Curtin University
The finding doesn’t conform to current theories about black hole formation and stellar development in binary systems as its mass is greater than the limit imposed on such an object.
How Cygnus X-1 Challenges Theories of Stellar Evolution
The team chanced on their finding whilst conducting an ambitious project to observe Cygnus X-1 almost continuously over a full 5.6-day orbit with the network of radio telescopes that comprise VLBA and X-ray telescopes. The aim of the research was to better understand how gas being fed into a black hole from a binary partner via a spiraling accretion disc connects to powerful jets of material that launch out from near the central region at near light speed.
“We had not originally aimed to refine the distance and the mass of the black hole but realised that our data would allow us to do so, by accounting properly for the effects of the black hole orbit. But there is still a wealth of data from this rich observing campaign that we are looking to analyse more fully.”
Professor James Miller-Jones, ICRAR, Curtin University
“Black holes form from the deaths of the most massive stars when they run out of fuel and gravity takes over,” says Miller-Jones. “The mass of the resulting black hole is set by the initial mass of the star from which it formed — which we call the progenitor star — the amount of mass that star lost in winds over its lifetime, and any interactions with a nearby companion star.”
Miller-Jones continues, saying massive stars launch very powerful winds from their surfaces, which leads to significant mass loss over their few-million year lifetimes. Some of the later phases of star’s evolution have particularly strong winds — determined by the abundance of elements heavier than helium in the gas from which the star was formed. More heavy elements mean stronger winds, and ultimately, a less massive star immediately before gravitational collapse.
While some stars can also lose further mass in supernova explosions as they collapse to form a black hole, the evidence suggests that in Cygnus X-1, there was no explosion, and the star collapsed directly into a black hole,” says Miller-Jones. “The stronger the stellar winds during the late evolutionary phases of the star, the less massive we would have expected the black hole to be.”
At first, the team wasn’t totally aware of just how significant their discovery of mass disparities in the Cygnus X-1 binary system was. “I think that our biggest surprise was when we appreciated the full implications of our measurements,” Miller-Jones says. “As observational astronomers, my team and I had already found that we could revise the source distance and the black hole mass. However, it was not until I visited a colleague, Professor Ilya Mandel of Monash University, who is a theoretical astronomer, that we realised how important this actually was.”
Mandel–co-author on the resulting paper– realised that a 21-solar mass black hole was too massive to form in the Milky Way with the constraints in place due to the current prevailing estimates of the amount of mass lost by massive stars in stellar winds.
“The existence of such a massive black hole in our own Milky Way galaxy has shown us that the most massive stars blow less mass off their surface in winds than we had previously estimated. This improves our knowledge of how black holes form from the most massive stars.”
Professor James Miller-Jones, ICRAR, Curtin University
Cygnus X-1: No Stranger to Contraversy
The team’s findings have allowed them to put forward a scenario that would allow the formation of a 21 solar mass black hole in a binary system. “We suggest that the star that eventually collapsed into a black hole began its life a few million years ago with a mass of 55-75 times the mass of the Sun,” Miller-Jones tells ZME. “Over its lifetime, it was close enough to its companion–the current supergiant–that gas from its surface was transferred onto its companion. This removed the outer layers of the black hole progenitor and caused it to rotate more rapidly because the two stars were always keeping the same face towards one another.
“Eventually, possibly as recently as a few tens of thousands of years ago the progenitor star collapsed directly into a black hole–of close to its current mass of 21 times the mass of the Sun–without a supernova explosion.”
Professor James Miller-Jones, ICRAR, Curtin University
Additionally, as well as gaining an insight into the black hole’s birth, Miller-Jones believes the team’s results could also indicate how the system could end its life. “Finally, we considered the eventual fate of this system,” the paper’s lead author says. “While the current companion star may eventually form a black hole, the separation of the two stars is such that the two black holes are unlikely to merge on a timescale comparable to the age of the Universe.”
A companion paper appearing at the same time in the Astrophysical Journal will delve deeper into these elements of the research.
This isn’t the first time that Cygnus X-1, and more specifically its black hole, has sparked discussion in the fields of astronomy and cosmology. As speculation grew during that the intense X-ray source in the region was the result of a black hole, renowned physicist Stephen Hawking bet fellow scientist Kip Thorne–well known for his black hole work–in 1974 that Cygnus X-1 did not contain a black hole.
“This was a form of insurance policy for me. I have done a lot of work on black holes, and it would all be wasted if it turned out that black holes do not exist. But in that case, I would have the consolation of winning my bet, which would win me four years of the magazine Private Eye. If black holes do exist, Kip will get one year of Penthouse.”
Stephen Hawking, A Brief History of Time
Hawking lost the bet, conceding by breaking into Thorne’s office whilst he was on a trip to Russia and signing the framed bet.
The team now intend to apply the technique that led them to this finding to investigate further black holes. This should enable them to better understand how massive stars lose mass through stellar winds. With that said, as Cygnus X-1 is relatively unique in the Milky Way–as one of the few black holes so far detected in orbit with a massive companion star– Miller-Jones believes that they are unlikely to find any more binary systems in which the masses of the constituent star and black hole diverge so drastically from current estimates.
“Most excitingly for me, the advent of cutting-edge new telescopes such as the Square Kilometre Array radio telescope (SKA) will allow us to detect many more black holes, and study their properties, including how matter flows into and away from them, in more detail than ever before,” concludes Professor Miller-Jones. “It’s an exciting time to be in this field!”
Let’s start with the history of the universe (a very brief one). After the Big Bang, the Universe was essentially a hot soup of particles. Things started to cool down and eventually started forming hydrogen atoms. At some point, the universe became neutral and transparent, but because the clouds of hydrogen collapsed very slowly, there were no sources of light — it was a period of complete and utter universal darkness aptly called Dark Ages.
The famous dark matter slowly started to form structures that later became the first source of light in the universe. The emergence of these sources occurred in the Epoch of Reionization (EoR), around 500 million years after the Big Bang. Now, astronomers have found that formed not that long after this period.
Astronomers from China, the US, and Chile have now found a huge galaxy protocluster (a dense system of dozens of galaxies from the early universe that grows together) from the early days of the universe. Called the LAGER-z7OD1 cluster, it dates from a time when the universe was still a baby — only 770 million years old, early in its history. These objects are important tools that enable astronomers to examine the EoR.
The group that worked detecting these objects is called the Lyman Alpha Galaxies in the Epoch of Reionization (LAGER). Lyman Alpha Galaxies are very distant objects that emit radiation from neutral hydrogen and they are the components to find clusters that are so old.
LAGER primarily used the Dark Energy Camera (DECam) from the Cerro Tololo Inter-American Observatory (CTIO) 4-m Blanco telescope in Andes, Chile. They found out was it is a system with a redshift of 6.9 — here’s why that’s intriguing.
Redshift is a measure of how something is moving in space: if it moves away from us we see a longer wavelength, which means a positive redshift and a wavelength skewed towards red — if it is moving towards us, it means shorter wavelengths, a negative redshift, and a wavelength skewed towards blue. The bigger the redshift, the more distant it is from us.
The cluster has 21 galaxies and if you want to estimate distance, the volume is probably 51,480 Mpc³ (1 Mpc is almost 3 million light-years) and it’s about 3,700,000 billion times more massive than the Sun. In addition, it has an elongated shape which means subclusters merged to form the bigger structure.
It’s basically a gazillion miles from us, but a gazillion isn’t good enough for astronomers — they always want to know just how far away things are. In this case, however, an approximation will have to do.
The Plack Collaboration estimated that the EoR probably started at z=7.67. This estimation uses the polarization of the Comic Microwave Background photons, just like polarizing light with sunglasses, but with a level of sensitivity so high that the instruments to detect it must be at temperatures close to absolute zero. Another important conclusion came from search for quasars formed in this period, usually the many papers about it conclude that the end of the EoR was around z=6.
Lyman Alpha Galaxies and quasars are major findings to understand the EoR. The best sample of quasars we have now has only 50 quasars, not much to represent the EoR for the entire universe. LAGER-z7OD1 is an example of cluster which possibly formed in the middle of the process, until absolute certainty is obtained more observations like this one need to come.
It’s almost staggering to think that before 1925 humanity knew very little about the composition of the stars. In fact, we would develop the theories of quantum mechanics, special and general relativity before we knew what lay beneath the surface of the Sun.
The first scientist to develop an accurate theory of the composition of the stars was Cecilia Payne-Gaposchkin. Born Cecilia Helena Payne in a small English market town in Buckinghamshire in 1900, in doing so she would also develop the first accurate picture of the abundance of the elements hydrogen and helium throughout the Universe.
But, these remarkable discoveries were not met with the appreciation one would expect. Payne-Gaposchkin would be discouraged from publishing her findings by a male contemporary. The setback would be just one more obstacle for Cecilia to overcome.
Facing the prejudice and misogyny that typified society in general, and science and academia in particular, during the early 20th Century, Payne-Gaposchkin would show a resolve that led to her becoming the world’s foremost expert on variable stars and enable her to lay the groundwork for astrophysics.
Through sheer grit and determination, she would redefine our understanding of the composition of the stars and the Universe in general. Not bad for a scientist whose lectures weren’t even listed in her University’s course catalogue, who also had her wages by the same institute paid under ‘equipment costs.’
From Botany to Astronomy
Things could have been very different for Cecilia Payne-Gaposchkin. Her interest in science first manifested as a fascination with the natural world and botany. A hint towards her future as an astronomer and astrophysicist shone through when Cecilia was just ten and she watched, transfixed, as a meteor traversed the night sky.
Payne’s interest in nature was encouraged by her mother, Emma Leonora Helena Payne, after her father Edward passed away when she was just four years old. The death of her father, who drowned in a canal under questionable circumstances, left young Cecilia devastated and her mother to raise the future astronomer and her two siblings alone.
Emma strongly encouraged the education of her three children, of which Cecilia was the eldest, introducing them to literature at an early age. Cecilia’s traits as a scientist would be further bolstered by her experience at her first school ran by Elizabeth Edwards which strongly encouraged the memorization of facts and figures.
Beyond this, Ms Edwards would actively teach her pupils, including the girls, geometry and algebra. Young Cecilia revelled in the solving of quadratic equations.
“My mother had told me of the Riviera-trapdoor spiders and mimosa and orchids, and I was dazzled by a flash of recognition. For the first time, I knew the leaping of the heart, the sudden enlightenment, that were to become my passion.”
At the age of twelve, Cecilia was forced to move schools when her family relocated from Wendover to London. Her new school, St Mary’s College, Paddington, could not have been less like Ms Edward’s. Like her female contemporaries, at the Church of England school with its strong emphasis on religion and ‘traditional values’ Cecilia would be offered little in the way of educational stimulation and even less encouragement to embark on a career in science.
In fact, it was here that a male teacher would confidently tell Payne-Gaposchkin she would never achieve a career in science. A prediction that may well go down in history as one of the worst ever made by an educator.
Fortunately, at the age of 17, Payne-Gaposchkin would be asked to transfer to St. Paul’s Girls School in London. Though the move initially troubled her, it is here where her teachers would allow Cecilia to study elements of physics such as mechanics, dynamics, electricity and magnetism, light, and thermodynamics.
At St. Pauls she was encouraged by her teachers to pursue science, enabling her to obtain a scholarship to Newnham College in 1919 where she would study the slightly odd but eclectic mix of botany, chemistry, and astronomy.
Attending the college, part of Cambridge University, Payne-Gaposchkin soon became bored with botany. Her tutors taught the subject stiffly and rigidly, relaying information she already knew, thus providing Cecilia with little stimulation. She recalled, in particular, an incident in which she discovered a group of desmids whilst studying algae under a microscope. Asking her tutor for help in identifying the organisms, he simply responded that it was not within the remit of her studies so she should just ignore it.
Her decision to switch to astronomy as her major was solidified when she attended a lecture given by Cambridge’s renowned astronomer Sir Arthur Eddington.
Eddington had found fame journeying to the island of Príncipe off the west coast of Africa to examine a solar eclipse that would provide verification for Einstein’s theory of general relativity. The lecture was on the same subject and for Payne, it ignited her desire to study nature beyond the surface of our planet.
Cecilia approached Eddington asking for a research project. He set her the problem of integrating the properties of a model star, starting from initial conditions at the centre and working outward.
“The problem haunted me day and night. I recall a vivid dream that I was at the center of Betelgeuse, and that, as seen from there, the solution was perfectly plain; but it did not seem so in the light of day.”
Disappointed at not being able to solve the problem she took her calculations to Eddington incomplete. She need not have worried. Eddington revealed to her with a jovial smile that he had not been able to solve the conumdrum either and had spent years trying!
Building the foundations of Astrophysics
Eddington was just taken with Payne-Gaposchkin as she was with astronomy, seeing great potential in the young woman. Unfortunately, transferring to the class of Ernest Rutherford, Cecilia discovered that not all of Eddington’s colleagues would be as supportive.
Rutherford, who would go onto perform experiments that would reveal the structure of the atom, was extremely cruel to Payne–the only woman in his class–encouraging the other, exclusively male, students to mock and taunt her, something they did with relish.
Payne-Gaposchkin weathered the storm. She had already experienced what it was like to exist in a male-dominated world and had already overcome too much to fold under mere mockery.
And the indignities would nor end there. Despite completing her coursework, women were forbidden to obtain degrees in the United Kingdom in 1923. Thus Payne-Gaposchkin would have no paperwork to verify her academic achievements. Her chances of obtaining a master’s degree or PhD in the UK were slim to none.
It was upon attending a meeting of the Royal Astronomical Society that Cecilia’s options improved markedly. Its new director Harlow Shipley regaled Payne-Gaposchkin with tales of the opportunities that would await her were she to relocate across the Atlantic to the United States.
Cecilia needed little further encouragement. She was awarded the Pickering Fellowship through Harvard College, taking the small financial aid offered by the only scholarship exclusively for women at the time and using it to move to America. Her association with Havard would continue for many years and prove to be extremely fruitful. Indeed, she would come to consider Boston her second home.
Whilst working under the auspices of Shapely at Harvard College Observatory she continued her studies, finalising what would go on to be her doctoral thesis–Stellar Atmospheres.
In the work, Payne-Gaposchkin would be the first person to suggest that hydrogen was the most abundant element in the universe and the primary constituent of stars. At that time scientists had believed that the Sun and other stars had a chemical composition similar to that of the Earth’s crust. American physicist Henry Norris Russell has pioneered the idea that if earth’s temperature was raised to that of the Sun’s it would have a spectral signature the same as our star.
Payne-Gaposchkin’s finding bucked this idea and arose from the fact she had a much better understanding of atomic spectra than her contemporaries. Unfortunately, American Russell strongly disagreed with her conclusion and persuaded her to leave it out of her thesis.
Payne later reflected on her regret with regards to being persuaded not to publish her findings. It was not a mistake that Payne would never be convinced to make again.
“I was to blame for not having pressed my point. I had given in to Authority when I believed I was right. That is another example of How Not To Do Research. I note it here as a warning to the young. If you are sure of your facts, you should defend your position.”
For what it is worth, Russell too would go on to regret his decision to pressure Cecilia. Russell published a 1929 paper that credited Cecilia as Payne’s earlier work and her discoveries.
It must be one of the most heinous injustices in the history of astronomy that Russell is still to this day often wrongly credited with Payne-Gaposchkin’s discovery.
Russian-American astronomer Otto Struve later recognised the genius of Payne-Gaposchkin’s thesis, describing it as “the most brilliant PhD thesis ever written in astronomy.”
To The Stars and Beyond
In 1934 on a visit to Germany for an astronomy meeting Cecilia met a young Russian astronomer, Sergei Gaposchkin. The astronomer was an exile from his country of birth due to his political convictions, and Cecilia found his struggles to be an echo of her own. She was determined to help Sergei find a secure and consistent place to practice science.
Indeed, obtaining Sergei a visa as a stateless person, Cecilia found him a research position at Harvard. To the surprise of their colleagues, the two were married in late 1934. Initial doubts that the marriage wouldn’t last were ill-founded.
Cecilia Payne-Gaposchkin and Sergei Gaposchkin would go on to have three children and remained married until her death in 1979. The two would also form a solid partnership in research, authoring several papers and books together. They even started their own farm–though it’s undeniable that Sergei enjoyed the life of a farmer much more than Cecilia did.
The discovery of the abundances of hydrogen and helium in the Universe and the composition of the stars would not be Payne-Gaposchkin’s only substantial contribution to astronomy and the burgeoning field of astrophysics.
Following the completion of her doctorate, Payne-Gaposchkin would begin to study high luminosity stars in order to understand the composition of the Milky Way. The period marked the beginning of Payne-Gaposchkin’s fascination with variable stars–stars which display periodic brightness fluctuations over radically different periods of time– and novae. This specialization led to the book Stars of High Luminosity, published in 1930.
Cecilia and Sergei undertook an audacious investigation of variable stars, during the ’30s and ’40s, they would make nearly 1.3 million observations of variable stars, with Payne-Gaposchkin’s mind for memorizing facts and figures making her almost a walking compendium of such objects. One of their papers published in 1938 would be the ‘go-to’ tome on variable stars for decades.
During the 1960s, Cecilia and Sergei would shift their attention to the small irregular galaxies situated by the Milky Way–the Magellanic Clouds–and the variable stars located within it. They would make another staggering contribution to astronomy during this study, cataloguing over 2 million visual estimates of these star’s magnitudes.
In 1956, Payne-Gaposchkin would finally be awarded the title of professor, making her the first woman in Harvard’s history to receive such an accolade. She would also be made the chair of a department at Harvard, also the first woman to be recognised in this way. Whilst no one could disagree that the accolade was insultingly well overdue, it was a small positive step in the right direction, finally opening the door for female professors across the US.
The Legacy of Cecilia Payne- Gaposchkin
Despite waiting so long to be named a professor, Payne-Gadoschkin’s life would not be short on accolades. In 1934, the American Astronomical Society recognized her significant contribution to astronomy by awarding her Annie J. Cannon Prize.
In 1936 she would become a member of the American Philosophical Society, and the 1940s and 1950s marked the award of several honorary doctorates, that should not be viewed as merely consolation prizes for the actual doctorate that she had strived for and had been denied her.
Continuing her trailblazing progress for women in the sciences, in 1976 she would become the first woman to receive the Henry Russell Prize from the American Astronomical Society. The astronomer, who would publish over 150 papers and several books during her career, would receive a further honour in 1977 when the astroid 1974 CA–occupying the asteroid belt between Jupiter and Mars–was renamed 2039 Payne-Gaposchkin.
After her semi-retirement in 1966, Payne-Gaposchkin would continue to lecture inspiring the next generation of astronomers. Her final academic paper was published in 1977, just months before her death in December of that year.
During the course of her life, Cecilia Payne- Gaposchkin would change our understanding of the Universe in a way that was no less profound than her colleagues in physics did. Without doubt, her name, therefore, should be listed alongside luminaries such as Copernicus, Newton, and Einstein.
Yet, because of her gender, her genius was barely recognised during her lifetime and her name is still sadly omitted from many textbooks and is nowhere near as prominent as the names of her male counterparts or as her achievements demand.
It is abundantly clear, by becoming the first person to known the true composition of the universe, her star shines just as bright if not brighter as any other scientist. And without her, we still may not know why.
Dr. Eamonn Kerins, an astrophysicist from the University of Manchester, has an idea for the Search for Extraterrestrial Intelligence (SETI). It consists of a strategy called Mutual Detectability based on coordination game, a strategy in which both players make the same decision.
Imagine you’re at a concert and your phone battery is dead, but you need to find a friend. How do you do it?
Here’s an approach: both of can you employ the same strategy and find each other in the middle of the crowd. In this situation, both parties win a payoff for having the same desire and the same decisions. This is what Mutual Detectability is about. If two civilizations have enough knowledge of each other, it is likely they will try to communicate and reach each other. This type of strategy rationalization is the basis of game theory, and Kerins believes applying game theory to SETI could be a fruitful strategy.
Opposites don’t always atract
One obstacle for the civilizations looking for other civilizations has to do with technological advancement. When one civilization is more powerful than the other, the less powerful will feel less comfortable in making contact — for obvious reasons. Any civilization looking for others would have an incentive to listen, but not send out signals, so our galaxy might be full of listeners not able to find each other.
However, even if two civilizations are trying to find each other, they might not be able to if they use very different technologies. This could be avoided, says Kerins, if the more advanced civilization would use less-advanced signals. But you’d still need to actually be able to find them. This leads to the SETI paradox, if intelligent beings are looking for intelligent beings but not trying to reach out, then SETI is in vain.
Where to look?
Kerins points to the importance of the region of the Earth Transit Zone(ETZ). The idea is simple: not all planets in the universe can see us. If an alien civilization can observe us when our planet passes in front of the Sun and reduces its luminosity, they will be able to detect us. This is called the transit method, used by astronomers to detect exoplanets.
ETZ is the optimal area in which other beings could detect us in the galaxy using the transit method. Success in mutual detectability could mean detecting planets in the habitable zone and that are in the ETZ region. Similarly, we should focus on detecting potentially habitable planets that could be able to see us.
Good news is, there’s at least one planet that fits the bill.
K2-155 d is a Super-Earth in the habitable zone that happens to be in ETZ. The planet orbits an M dwarf star, the smallest type of star we know of, but it orbits it close enough to potentially have habitable temperatures. This type of star also makes the transit method easier to succeed, because a relatively small star has a clearer response to the transit. In other words, we see it blinking more clearly. That would be one starting to point SETI telescopes at.
But we already know many exoplanets. Only the Kepler mission discovered 2,662 planets in nearly 10 years of service. If we continue the search for planets and match the criteria stated by Dr. Kerins, our chances of communication would increase and the loneliness of Earth could end.
It’s one of the greatest scientific projects of the century and it just got the official green light. The Square Kilometre Array Observatory (SKAO) will be the largest and most complex radio telescope network in the world, with an estimated of cost $2.2 billion. Once built, it will offer us an unprecedented view of the universe.
The building initiative has 14 member countries and around 100 organizations spread across about 20 countries, all of which had their first meeting which was done online because of the coronavirus pandemic. SKAO has been discussed for over 30 years so the fact that it’s finally moving forward is a big deal, and not just for astronomers.
The telescope will have unprecedented sensitivity and it will pick up any extra-terrestrial transmissions. This could help astronomers answer important questions, from whether we are alone in the universe to what’s dark energy, an unknown form of energy that appears to be driving the cosmos apart at an accelerating rate
“Today marks the birth of a new observatory,” Phil Diamond, appointed first Director-General of SKAO, said in a statement. “And not just any observatory – this is one of the mega-science facilities of the 21st century. It is the culmination of many years of work. This is about participating in one of the great scientific adventures of the coming decades.”
At their first meeting, SKAO’s council approved a whole series of policies, regulations, and procedures that will make the observatory real — the boring, but very important things. But the key step is actually building the actual telescope. Member countries hope to send invitations to tender to the industry from July onwards, with the entire construction expected to be finished in about a decade.
The project is so astonishing in scope that it includes setting up radio receivers in two continents, far away from any machine that emits radio waves. One location will be the Karoo in South Africa’s Northern Cape, where 197 parabolic radio antennae, or dishes, will be built. The South African Radio Astronomy Observatory (SARAO) has already built 64 of them.
The other part of the project will be located in the Western Australian outback at Murchison. An impressive two meters tall low-frequency aperture array telescopes will be built there. Alongside the dishes in South Africa, this will create a collecting area spanning across two continents that allow the detection of very faint radio signals.
Blade Nzimande, Minister of Higher Education, Science & Innovation of South Africa, a member of SKAO, said in a statement: “The SKA project will act as a catalyst for science, technology and engineering innovation, providing commercial opportunities to local high-tech industry, and creating the potential to put Africa on the map as a global science and innovation partner.”
The council meeting that kicked off the project was led by the countries that have ratified the SKA treaty. These are Australia and South Africa, as the telescope’s host nations; Italy, the Netherlands, Portugal; and the United Kingdom, which is where the organization has its headquarters at the Jodrell Bank radio observatory. Other countries joined the meeting as observers.
The financing for the project is coming from all the member countries. They estimate construction and operation will consume about $2.4 billion over the next decade. It will be by far the largest radio telescope array ever constructed, with a total collecting area of well over one square kilometer. We’ll have to wait a few years to see it, but the results could be quite significant.
Astronomers have discovered a unique system of exoplanets in which all but one of the planets orbit their parent star in a rare rhythm. The finding could force us to revise our ideas of how planets–including those in our own solar system–form.
The team–including astronomers from the University of Bern and the University of Geneva–used a combination of telescopes and the European Southern Observatory’s (ESO) Very Large Telescope (VLT) to observe the star TOI-178, 200 light-years away from us in the constellation Sculptor.
Upon first glance, the astronomers believed that the star was orbited by just two exoplanets, both of which had the same orbits. Closer inspection revealed something surprising, however — six planets, five of which are locked in a rhythmic dance with each other.
“Through further observations, we realised that there were not two planets orbiting the star at roughly the same distance from it, but rather multiple planets in a very special configuration,” says lead researcher Adrien Leleu, University of Bern.
This rhythm reveals a star system that has remained undisturbed by cosmic events since its birth. But, even within this system exists a measure of chaos, with the compositions of the constituent planets displaying some disharmonious densities that are just as rare as their harmonious orbits.
The system consists of planets ranging from one to three times the size of Earth, with masses that range from 1.5 to 30 times that of our planet. Some are rocky and larger than Earth–so-called Super-Earths. Others are gaseous like the solar system’s outer bodies, but much smaller–a class of exoplanets called Mini Neptunes.
“This contrast between the rhythmic harmony of the orbital motion and the disorderly densities certainly challenges our understanding of the formation and evolution of planetary systems,” Leleu adds.
The team’s research is published in the journal Astronomy & Astrophysics.
Exoplanets in Resonance
All the exoplanets around TOI-178, barring the one closest to the star itself, are exhibiting a resonance can be observed in the repeated patterns in their orbits. These repeating orbits mean that the planets align at regular intervals as they loop their parent star.
A similar–albeit less complex– resonance can be found in our own solar system, not with planets, but with three of the moons of Jupiter. Io completes four full orbits for every orbit of Ganymede, whilst also completing two full orbits for every orbit of Europa. This is what is known as a 4:2:1 resonance.
TOI-178’s five outer planets possess a far more complex chain of resonance than these moons, however. The exoplanets exist in an 18:9:6:4:3 resonance. This means the first exoplanet in the chain–the second closest to the star overall–completes 18 orbits as the second in the chain completes nine, the third completes six, and the fourth completes 4, and the fifth (the sixth planet overall) completes three orbits.
The team were able to take the resonance of the four planets described above and use it to discover the fifth in the chain, which is the sixth and final planet overall.
The team believes that the exoplanet’s rhythmic orbits could teach them more the system than its current state, though. It could even provide them with a window into its past. “The orbits in this system are very well ordered, which tells us that this system has evolved quite gently since its birth,” explains co-author Yann Alibert from the University of Bern.
In fact, the resonance of the system shows that it has remained relatively undisturbed since its formation. Were it to have been significantly disturbed earlier in its life–by a giant impact or the gravitational influence of another system, for example– the fragile configuration of its orbits would have been obliterated.
Disharmony and Disorder Enter the Picture
It’s not all harmony within the TOI-178 exoplanets., however. Whilst their arrangements and neat and well-ordered, the densities and compositions of the individual exoplanets are much more disordered. It’s a disorder that is very different from what we observe in our solar system.
“It appears there is a planet as dense as the Earth right next to a very fluffy planet with half the density of Neptune, followed by a planet with the density of Neptune. It is not what we are used to,” team member Nathan Hara, University of Geneva, says, describing a system comprised of Super Earths and Mini Neptunes.
As is the case with most exoplanets, the planets in the TOI-178 system were difficult to spot. The team used data collected by the European Space Agency’s CHEOPS satellite, launched in December 2019, with instruments at the VLT located in Chile’s Atacama Desert region.
In addition to this data, the team used two of the most common techniques used by astronomers to spot exoplanets. Examing the light emitted by a parent star and how it dips indicates when a planet is transitting in front of it. Also, orbits of exoplanets around a parent star can cause it to ‘wobble’–something that can be seen in its light profile.
This combination of methods allowed the team to discover that the exoplanets in TOI-178 are orbiting their parent star far more rapidly and at a much closer distance than Earth orbits the Sun.
The innermost planet, the one not part of the resonant chain, is the fastest and orbits TOI-178 in just a matter of days. The slowest has an orbit that takes ten times this period to complete.
None of the planets seems to be orbiting in what is believed to be TOI-178’s habitable zone–the area in which water can exist as a liquid. But, the team believes that studying the resonance chain could uncover additional planets in this system, some with orbits that bring them within this region.–also colourfully nicknamed the ‘Goldilocks zone’ because it is neither too hot not too cold.
The researchers will continue to investigate this unique and extraordinary system and suggest that it could be a target for intense observation with the ESO’s Extremely Large Telescope (ELT) when it begins operations later this decade.
The ELT should be able to allow researchers to directly image the exoplanets in Goldilocks zones around stars like TOI-178 as well as study their atmospheres in detail.
This could reveal that the TOI-178 holds even more secrets than this study has revealled.
A. Leleu, Y. Alibert, N. C. Hara, et al, ‘Six transiting planets and a chain of Laplace resonances in TOI-178,’ Astronomy & Astrophysics, , (doi: 10.1051/0004-6361/202039767).
The star system of Trappist-1 is home to the largest group of Earth-like planets ever discovered elsewhere in the Universe by astronomers. This means that investigating these seven rocky worlds gives us a good idea of how common exoplanets with similar compositions to our own are in the Milky Way and the wider cosmos.
New research has revealed that these planets, which orbit the Trappist-1 star 40 light-years away from Earth, all have remarkably similar compositions and densities. Yet, all are less dense than Earth.
The results could indicate these are worlds with much more water than is found on earth, or possibly even that these planets are composed almost entirely of rust.
This similarity between the exoplanets makes the Trappist-1 system significantly different from our own solar system which consists of planets with radically compositions and densities. Trappist-1’s worlds are dense, meaning they are like the rocky planets in our solar system, Earth, Mars, Venus, and Mercury. The system seems to be lacking larger gas dominated planets like Jupiter, Saturn, Uranus and Neptune.
The finding, documented in a paper published in the Planetary science Journal shows how the system, first discovered in 2016, offers insight into the wide variety of planetary systems that could fill the Universe.
“The new observations allowed us to use transit data from a much longer time span than was available to us for the 2018 calculations,” explains Simon Grimm of the University of Bern, who as well as being involved in the current study, was part of a 2018 team that provided the most accurate calculation of the masses of the seven planets thus far. “With the new data, we were able to refine the mass and density determinations of all seven planets.
“It turned out that the derived densities of the planets are even more similar than we had previously expected.”
Seven Exoplanets with Similar Densities
The similarity in densities observed in the Trappist-1 exoplanets seen by the astronomers hailing from the Universities of Bern, Geneva and Zurich, indicates that there is a good chance they are composed of the same materials at similar ratios.
These are the same materials that we believe form most terrestrial planets, iron, oxygen, magnesium, and silicon. But there is a significant difference between our terrestrial world and the Trappist-1 exoplanets.
The planets in the Trappist-1 system appear to be about 8% less dense than the Earth. This suggests that the materials that comprise them exist in different ratios than they do throughout our home planet.
This difference in density could be the result of several different factors.
One of the possibilities being investigated by the team is that the surfaces of the Trappist-1 exoplanets could be covered with water, reducing their overall density. Combining the planetary interior models with the planetary atmosphere models, the team was able to evaluate the water content of the seven TRAPPIST-1 planets with what Martin Turbet, an astrophysicist at the University of Geneva and co-author of the study describes as “a precision literally unprecedented for this category of planets.”
For the Trappist-1 system’s four outermost planets, should water account for the difference in density, the team has estimated that water would account for 5% of their overall masses. This is considerably more than the 0.1% of Earth’s total mass made up of water.
Rust Nevers Sleeps for the Trappist-1 Planets
Another possibility that could explain why the Trappist-1 exoplanets have lower densities than Earth is the fact that they could be composed of less iron than our planet is–21% rather than the 32% found in the Earth.
It’s also possible that the iron within the seven exoplanets could be bonded with oxygen forming iron oxides–commonly known as rust. This additional oxygen would reduce the planet’s densities.
Iron oxides give Mars its rust-red colour, but they are pretty much confined to its surface. Its core is comprised of non-oxidized iron like the solar system’s other terrestrial planets. If iron-oxide accounts for the seven exoplanet’s lower densities it implies that these worlds are rusty throughout and lacking solid non-oxidized iron cores.
“The lower density might be caused by a combination of the two scenarios – less iron overall than and some oxidized iron,” explains Eric Angol, an astrophysicist at the University of Washington and lead author of the new study. “They might contain less iron than Earth and some oxidized iron like Mars.”
Angol also points out that the Trappist-1 planets are likely to have a low-water content, an idea supported by previous research. “Our internal and atmospheric structure models show that the three inner planets of the TRAPPIST-1 system are likely to be waterless and that the four outer planets have no more than a few per cent water, possibly in liquid form, on their surfaces,” says Turbet.
This seems to favour the theory that the lower density of the Trappist-1 planets is a result of one or both of the iron scenarios suggested by the researchers.
There’s Still a Lot to Learn from Trappist-1
Since its discovery in 2o16, the Trappist system has been the subject of a wealth of observations made by both space and ground-based telescopes alike. Before it was decommissioned at the start of January 2020 the team used the Spitzer Space Telescope to collect their data. This telescope, operated by NASA’s Jet Propulsion Laboratory, alone has clocked in more than 1,000 hours of targeted observations of the exoplanets.
This new study demonstrated the importance of studying systems such as Trappist-1 for extended periods of time.
Caroline Dorn, an astrophysicist at the University of Zurich also highlights the fact that studying systems like this could answer questions about the habitability of exoplanets and the possibility of life elsewhere in the Universe.
“The TRAPPIST-1 system is fascinating because around this one star we can learn about the diversity of rocky planets within a single system,” concludes Dorn. “And we can actually learn more about an individual planet by studying its neighbours as well, so this system is perfect for that.”
“The night sky is full of planets, and it’s only been within the last 30 years that we’ve been able to start unravelling their mysteries, also for determining the habitability of these planets.”
Agol. E., Dorn. C., Grimm. S. L., et al, ‘Refining the transit timing and photometric analysis of TRAPPIST-1: Masses, radii, densities, dynamics, and ephemerides,’ Planetary Science Journal, [https://arxiv.org/abs/2010.01074]