Category Archives: Astronomy

Artist’s impression of binary black holes about to collide. Image credit: Mark Myers, ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav).

Gravitational waves reveal largest black hole merger and the first intermediate-mass black hole

Gravitational waves have been detected from what appears to be the largest black hole merger ever observed. The powerful and previously unobserved hierarchical merger resulted in  an intermediate-mass black hole, an object never before detected.

A massive burst of gravitational waves equivalent to the energy output of eight Suns has been detected by the LIGO laser interferometer. Researchers at LIGO and its sister project VIRGO believe that the waves originate from a merger between two black holes. But, this isn’t your average black hole merger (if there is such a thing). The merger — identified as gravitational wave event GW190521 — is not only the largest ever detected in gravitational waves — but it is also the first recorded example of what astrophysicists term a ‘hierarchical merger’ occurring between two black holes of different sizes, one of which was born from a previous merger.

“This doesn’t look much like a chirp, which is what we typically detect,” says Virgo member Nelson Christensen, a researcher at the French National Centre for Scientific Research (CNRS), comparing the signal to LIGO’s first detection of gravitational waves in 2015. “This is more like something that goes ‘bang,’ and it’s the most massive signal LIGO and Virgo have seen.”

GW190521 facts courtesy of LIGO-VIRGO (R. Ewing, R. Huxford, D. Singh
The Pennsylvania State University)
GW190521 facts courtesy of LIGO-VIRGO (R. Ewing, R. Huxford, D. Singh
The Pennsylvania State University)

Even more excitingly, it seems that black hole birthed in the event has a mass of between 100–1000 times that of the Sun, putting it in the mass range of an intermediate-mass black hole (IMBH). Something that researchers have theorised about for decades, but up until now, have failed to detect.

The gravitational wave signal–spotted by LIGO on 21st May 2019–appears to the untrained eye as little more than four short squiggles that lasted little more than one-tenth of a second, but for Alessandra Buonanno, Principal Investigator of the LIGO Scientific Collaboration, whose group focuses on the development of highly-accurate waveform models, it holds a wealth of information. “It’s amazing, but from about four gravitational-wave cycles, we could extract unique information about the astrophysical source,” she tells ZME Science.

“The waves are fingerprints of the source that has produced them.”

Alessandra Buonanno, Principal Investigator of the LIGO Scientific Collaboration.

As well as containing vital information about black holes and a staggering merger event, as the signal originated 17 billion light-years from Earth and at a time when the Universe was half its current age, it is also one of the most distant gravitational wave sources ever observed. The incredible distance the signal has travelled may initially seem at odds with the fact that the Universe is only 14.8 billion years old, but the disparity arises from the fact our universe is not static but is expanding.

A still from a numerical relativity simulation for GW190521 showing the gravitational waves emitted just before merger, overlaid with the signal as observed by the detectors. This is the largest binary system yet detected as shown by the horizons of this event compared to several previous events. (EPO)
A still from a numerical relativity simulation for GW190521 showing the gravitational waves emitted just before merger, overlaid with the signal as observed by the detectors. This is the largest binary system yet detected as shown by the horizons of this event compared to several previous events. (Deborah Ferguson, Karan Jani, Deirdre Shoemaker, Pablo Laguna, Georgia Tech, MAYA Collaboration)

Details of the international team’s important findings are featured in a series of papers publishing in journals such as Physical Review Letters, and The Astrophysical Journal Letters, today.

Missing Intermediete-Mass Black Holes

Thus far, the black holes discovered by astronomers have either been those with a mass inline with that of larger stars–so-called stellar-mass black holes, or supermassive black holes, with masses far exceeding this. Black holes that exist between these masses have remained, frustratingly hidden. Until now.

“The LIGO and Virgo collaborations detected a gravitational wave corresponding to a very interesting black hole merger. This was named GW190521 and corresponds to two large black holes during the final orbit and merger,” Pedro Marronetti, program director for gravitational physics at the National Science Foundation (NSF) responsible for the oversight of LIGO, tells ZME Science.

“What makes GW190521 extraordinary in comparison to other gravitational wave events is the mass of the black holes involved, the product of the merger is a 142 solar mass black hole and the first object of its kind with mass above 100 solar masses but below a million solar masses to be discovered.”

Pedro Marronetti, program director for gravitational physics, the National Science Foundation (NSF)

Thus, the resultant black hole of 142 solar masses  exists in that crucial, thus far undetected, mass range indicating an intermediate-mass black hole (IMBH).

“These black holes, heavier than 100 solar masses but much lighter than the supermassive black holes at the centre of galaxies — which can be millions and billions of solar masses — have eluded detection until now,” Marronetti says. “Additionally, the heavier of the original black holes with 85 solar masses also presents an enigma.”

Pair Instability and Hierarchical Black Hole Mergers

The enigma that Marronetti refers to is the fact that heavier of the two black holes that entered the merger, is of a size that suggests it too must have been created by a merger event between two, even smaller, black holes. “The most common channel of formation of black holes involves heavy stars that end their lives in supernova explosions,” the NSF program director points out. “However, this formation channel prevents the creation of black holes heavier than 65 solar masses but lighter than 130 solar masses due to a phenomenon called ‘pair-instability’.”

This graphic shows the masses of black holes detected through electromagnetic observations (purple), black holes measured by gravitational-wave observations (blue), neutron stars measured with electromagnetic observations (yellow), and neutron stars detected through gravitational waves (orange). GW190521 is highlighted in the middle of the graphic as the merger of two black holes that produced a remnant that is the most massive black hole observed yet in gravitational waves. [Image credit: LIGO-Virgo/Northwestern U./Frank Elavsky & Aaron Geller]
This graphic shows the masses of black holes detected through electromagnetic observations (purple), black holes measured by gravitational-wave observations (blue), neutron stars measured with electromagnetic observations (yellow), and neutron stars detected through gravitational waves (orange). GW190521 is highlighted in the middle of the graphic as the merger of two black holes that produced a remnant that is the most massive black hole observed yet in gravitational waves. [Image credit: LIGO-Virgo/Northwestern U./Frank Elavsky & Aaron Geller]

As nuclear fusion ceases, there is no longer enough outward radiation pressure to prevent gravitational collapse. “The star suddenly starts producing photons that are energetic enough to create electron-positron pairs,” Marronetti explains. “These photons, in turn, create an outward pressure that is not strong enough to stop the star from collapsing violently due to its self-gravitational pull.”

This results in a difference in gravitational pressure between the star’s core and its outer layers. As a massive shock travels through these ‘puffed out’ outer layers they are blown away in a massive explosion. With smaller stars, this leaves behind an exposed core that becomes a stellar remnant such as a white dwarf, neutron star or black hole. But if the star is a range above 130 solar masses, but below 200 solar masses, the result is more disastrous.

“The resulting supernova explosion completely obliterates the star, leaving nothing behind– no black hole or neutron star is produced,” Marronetti says. “It will take stars heavier that 200 solar masses to collapse into black hole fast enough to avoid this complete disintegration.”

LIGO and Virgo have observed their largest black hole merger to date, an event called GW190521, in which a final black hole of 142 solar masses was produced. This chart compares the event to others witnessed by LIGO and Virgo and indicates that the remnant of the GW190521 merger falls into a category known as an intermediate-mass black hole – and is the first clear detection of a black hole of this type. Intermediate-mass black holes, which have previously been predicted theoretically, would have masses between those of stellar-mass black holes and the supermassive ones at the hearts of galaxies. Image credit: LIGO/Caltech/MIT/R. Hurt (IPAC)
LIGO and Virgo have observed their largest black hole merger to date, an event called GW190521, in which a final black hole of 142 solar masses was produced. This chart compares the event to others witnessed by LIGO and Virgo and indicates that the remnant of the GW190521 merger falls into a category known as an intermediate-mass black hole – and is the first clear detection of a black hole of this type. Intermediate-mass black holes, which have previously been predicted theoretically, would have masses between those of stellar-mass black holes and the supermassive ones at the hearts of galaxies. Image credit: LIGO/Caltech/MIT/R. Hurt (IPAC)

As Marronetti points out; this means that the 85-solar mass back hole could only be formed by the merger of two smaller black holes, as at these masses, collapsing stars can’t form black holes. “This is a quite unusual event that can only occur in regions of dense black hole population such as globular clusters,” the researcher adds. “GW190521 is the first detection that is likely to be due to this ‘hierarchical merger’ of black holes.”

Marronetti continues by explaining that a hierarchical merger consists of one or more black holes that were produced by a previous black hole merger. This hierarchy of mergers allows for the formation of progressively heavier and heavier black holes from an original population of small ones.

“We don’t really know how common these hierarchical mergers are since this is the first time we have direct evidence of one. We can only say that they are not very common.”

Pedro Marronetti, program director for gravitational physics, the National Science Foundation (NSF)

LIGO Delivering Discoveries and Surprises

The team uncovered the unusual nature of this particular merger by assessing the gravitational wave signal with a powerful state of the art computational models. Not only did this reveal that GW190251 originates from the most massive black hole merger ever observed and that this was no ordinary merger but a hierarchical merger, but also crucial information about the black holes involved in the event.

“The signal carries information about the masses and spins of the original back holes as well as their final product,” Marronetti adds, alluding to the fact that the LIGO -VIRGO team were able to measure that spin and determine that as the black holes circled together, they were also spinning around their own axes. The angles of these axes appeared to have been out of alignment with the axes of their orbit. This misaligned spin caused the black holes to ‘wobble’ as they moved together.

Artistic interpretation of the binary black hole merger responsible for GW190521. The space-time, figured by a fabric on which a view of the cosmos is printed, is distorted by the GW190521 signal. The turquoise and orange mini-grids represent the dragging effects due to the individually rotating black holes. The estimated spin axes, or self-rotations, of the black holes are indicated with the corresponding colored arrows. The background suggests a star cluster, one of the possible environments where GW190521 could have occurred. Credits: Raúl Rubio / Virgo Valencia Group / The Virgo Collaboration.
An artistic interpretation of the binary black hole merger responsible for GW190521. The space-time, figured by a fabric on which a view of the cosmos is printed, is distorted by the GW190521 signal. The turquoise and orange mini-grids represent the dragging effects due to the individually rotating black holes. The estimated spin axes, or self-rotations, of the black holes, are indicated with the corresponding coloured arrows. The background suggests a star cluster, one of the possible environments where GW190521 could have occurred. Credits: Raúl Rubio / Virgo Valencia Group / The Virgo Collaboration.)

“Our waveform models were used to detect GW190521 and also to interpret its nature, extracting the properties of the source, such as masses, spins, sky location, and distance from Earth. For the first time, the waveform models included new physical effects, notably the precession of the spins of the black holes and higher harmonics,” Buonanno says. “What we mean when we say higher harmonics is like the difference in sound between a musical duet with musicians playing the same instrument versus different instruments.

“The more substructure and complexity the binary  has — for example, black holes with different masses or spins—the richer is the spectrum of the radiation emitted.”

Alessandra Buonanno, Principal Investigator of the LIGO Scientific Collaboration.

Unanswered Questions and Future Investigations

Even with the staggering amount of information the team has been able to collect about the merger that gave rise to the signal GW190251, there are still some unanswered questions and details that must be confirmed.

The LIGO-VIRGO detectors use two very distinct methods to search the Universe for gravitational waves, an algorithm to pick out a specific wave pattern most commonly produced by compact binary mergers, and more general ‘burst’ searches. The latter searches for any signal ‘out of the ordinary’ and it’s the mechanism via which the researchers found GW190215.

Morronetti expresses some surprise that the methods used by the team were able to unlock these secrets, believing that this result demonstrates the versatility of LIGO. “My main surprise was that this event was detected using a search algorithm that was not specifically created to find merger signals,” says the NSF director. “This is the first detection of its kind and shows the capability of LIGO to detect phenomena beyond compact mergers.”

 “This is of tremendous importance since it showcases the instrument’s ability to detect signals from completely unforeseen astrophysical events. LIGO shows that it can also observe the unexpected.”

Pedro Marronetti, program director for gravitational physics, the National Science Foundation (NSF)


This leaves open the small chance that the signal was created by something other than a hierarchical merger. Perhaps something entirely new. The authors hint at the tantalising prospect of some new phenomena, hitherto unknown, in their paper, but Marronetti is cautious: “By far, the most likely cause is the merger of two black holes, as explained above. However, this is not as certain as with past LIGO/Virgo detections.

“There is still the small chance that the signal was caused by a different phenomenon such as a supernova explosion or an event during the Big Bang. These scenarios are possible but highly unlikely.”

Confirming the nature of the event that gave rise to the GW190251 signal is something that the LIGO team will be focusing on in the future as the interferometer also searches for similar events via the gravitational waves they emit. “

With GW190521, we have seen the tip of the iceberg of a new population of black holes,” Buonanno says, adding that LIGO’s next operating run (O4) will explore a volume of space 3 times larger than the current run (O3). “Having access to a larger number of events, which were too weak to be observed during O3, will allow us to shed light on the formation scenario of binary black holes like GW150921.”

It's getting crowded up there. A plot of space debris around the Earth. (NASA)

Scientists spot space debris in daylight, helping satellites ‘social distance’

It’s really getting crowded up there! The immediate area around Earth is cluttered with space debris, with recent estimates suggesting almost 4,000 man-made satellites in a near-Earth orbit, only one-third of which are currently operational. These non-operational units are subject to leakage, fragmentation and even explosions — further littering the immediate region around our planet. On top of this is a further population of near 20,000 known space debris objects. 

If humanity is going to continue to exploit the space immediately surrounding the Earth measures need to be taken to avoid this space debris. Collisions between this space junk and operating satellites aren’t just costly and damaging, they also create more debris. Now researchers at the University of Bern have made a breakthrough that just might help satellites avoid just collisions. 

The Bern team used the geodesic laser at Optical Ground Station and Geodynamics Observatory Zimmerwald to spot space debris in the daylight. (© Universität Bern / Université de Bern / University of Bern, AIUB)
The Bern team used the geodesic laser at Optical Ground Station and Geodynamics Observatory Zimmerwald to spot space debris in the daylight. (© Universität Bern / Université de Bern / University of Bern, AIUB)

The Bern team is the first in the world to successfully determine the distance from Earth to a piece of space junk in daylight. The researchers performed the feat on June 24th using a geodesic laser fired from Swiss Optical Ground Station and Geodynamics Observatory Zimmerwald. The achievement opens up the possibility of spotting space debris during the day, this means that possible collisions between satellites and space debris can be identified early and mitigation strategies such as evasive manoeuvres can be implemented earlier. 

Being Evasive

Spotting space debris during the day should help prevent events such as the collision that occurred between the operational communications satellite Iridium 33 and the obsolete Cosmos 2251 communications satellite in 2009. Occurring at an altitude of 800 km over Siberia the impact at 11.7 km/s created a cloud of over 2000 pieces of debris — each larger than 10 cm in diameter. Within a matter of months, this cloud of debris had spread across a wide area, and it has been a threat to operational satellites ever since. 

Simulations performed at Lawrence Livermore National Lab on the Testbed Environment for Space Situational Awareness (TESSA) show the collision between Iridium 33 and the Cosmos 2251 communications satellite and the space debris it created. (Lawrence Livermore National Lab)

But one positive did come out of the event, it made both scientists and politicians wake-up to the fact that the problem of space debris can no longer be ignored.

In fact, the risk of collision with space junk in certain orbits around the Earth is so great, that evasive manoeuvres are commonplace. The ESA alone receives thousands of collision warnings for each satellite in its fleet per year! This leads to satellites performing dozens of evasive acts each year. But, it’s vitally important to accurately assess when evasive action is actually needed as they can be costly and time-consuming to perform. 

“The problem of so-called space debris — disused artificial objects in space — took on a new dimension,” says Professor Thomas Schildknecht, head of the Zimmerwald Observatory and deputy director of the Astronomical Institute at the University of Bern. “Unfortunately, the orbits of these disused satellites, launcher upper stages or fragments of collisions and explosions are not known with sufficient accuracy.”

Thus, as well as reducing collision risk, daytime observations of space debris could mean that unnecessary evasive action is avoided. There could be another benefit to early debris detection too. 

Many researchers are currently investigating the possibility of missions to clear space debris. One such example is the work of Antônio Delson Conceição de Jesus and Gabriel Luiz F. Santos, both from the State University of Feira de Santana, Bahia, Brazil, recently published in the journal EPJ Special Topics. The pair modelled the complex rendezvous manoeuvres that would be required to bring a ‘tug vehicle’ into contact with space junk. Better positioning debris clusters could assist these efforts considerably.

Fun with Lasers

Currently, the position of space debris can only be estimated with a precision of around a few hundred metres, but the team from Bern believe that using the satellite laser ranging method they employed to make their daylight measurement, this margin of error can be slashed down to just a few meters, a massive improvement in accuracy. 

“We have been using the technology at the Zimmerwald Observatory for years to measure objects equipped with special laser retroreflector,” Schildknecht says, adding that these measurements were also previously only possible to make at night. “Only a few observatories worldwide have succeeded in determining distances to space debris using special, powerful lasers to date.”

The Zimmerwald Laser and Astrometry Telescope ZIMLAT in Zimmerwald, which is used for distance measurement to space debris objects. (© Universität Bern / Université de Bern / University of Bern, AIUB)
Example of a “string of pearls” of photons reflected by the target debris object in the “sea of sky background photos”. (© Universität Bern / Université de Bern / University of Bern, AIUB)

Despite providing more accurate measurements, geodetic laser systems such as the one at the Zimmerwald observatory employed by the researchers are actually at least one order of magnitude less powerful than specialized space debris lasers. Additionally, detecting individual photons diffusely reflected by space debris amid the sea of daylight photons is no mean feat.

These problems were overcome by the use of highly sensitive scientific CMOS camera with real-time image processing to actively track the space junk, and a real-time digital filter to detect the photons reflected by the object.

“The possibility of observing during the day allows for the number of measures to be multiplied. There is a whole network of stations with geodetic lasers, which could in future help build up a highly precise space debris orbit catalogue,” Schildknecht concludes. “More accurate orbits will be essential in future to avoid collisions and improve safety and sustainability in space.”

Comet NEOWISE Comes into Focus for a Close-up

Time is running out to catch a glimpse of the comet NEOWISE. The comet — the brightest object to grace the skies over the Northern Hemisphere in 25 years — will soon disappear from view. At least as far as the naked eye is concerned. Fortunately, the Hubble Space Telescope is on hand to capture stunning images of the comet — discovered on March 27th by NASA’s Wide-field Infrared Survey Explorer (WISE) space telescope during its mission to search for near-Earth objects. 

Hubble Captures a stunning close-up Comet NEOWISE (NASA, ESA, Q. Zhang (California Institute of Technology), A. Pagan (STScI))
Hubble Captures a stunning close-up Comet NEOWISE (NASA, ESA, Q. Zhang (California Institute of Technology), A. Pagan (STScI))

The image taken by Hubble on 8th August — which represents the closest ever taken of the comet since it first lit up the sky — shows NEOWISE as it sweeps past the Sun. This is the first time that astronomers have managed to capture such a bright object as it passes our star.

Hubble snapped the object as it rapidly makes its way out of the solar system, with it not scheduled to return for 6,800 years. The comet caused a stir amongst amateur star watchers and the general public as it was visible with the naked eye under the right conditions.

“Nothing captures the imagination better than actually seeing its tails stretching into the sky in person,” Qicheng Zhang,  a graduate student studying planetary science at Caltech, Pasadena, CA, who has been heavily involved in the study of NEOWISE. “The comet last came around about 4,500 years ago. This was around when the Egyptian pyramids were being built.”

“My research area covers comets and their evolution under solar heating,” Zhang explains to ZME Science. “I also like to keep track of potentially bright comets to actually see in the sky, which included this particular comet.”

Colour image of the comet taken by Hubble on 8 August 2020 within the frame of a ground-based image of the comet that was taken from the Northern Hemisphere on 18 July 2020. (NASA, ESA, Q. Zhang (California Institute of Technology), A. Pagan (STScI), and Z. Levay)
Colour image of the comet taken by Hubble on 8 August 2020 within the frame of a ground-based image of the comet that was taken from the Northern Hemisphere on 18 July 2020. (NASA, ESA, Q. Zhang (California Institute of Technology), A. Pagan (STScI), and Z. Levay)

The image shows NEOWISE’s halo of glowing gas and dust illuminated by light from the Sun surrounding the icy nucleus of the comet, too small at little more than 4.8km across to be fully resolved by the telescope. In contrast, the dust halo that surrounds the comet’s heart is too large to be fully resolved by the space telescope, with its diameter measuring an estimated 18,000 km.

Zhang points out that as NEOWISE moves past the Sun, there is a chance we could still glimpse its icy core: “As the comet recedes from the Sun, the dust with clear and reveal the solid nucleus currently buried within, providing an opportunity to directly observe the source of all the activity that made the comet impressive last month.”

Let’s Stick Together: Why NEOWISE Survived and ATLAS Didn’t

Previous attempts to capture other bright comets as they pass the Sun have failed because these objects have disintegrated as they passed too close to the star. This break-up is driven by both the incredible heat of the Sun causing the icy heart of the comets to fragment, and the powerful gravitational influence of our star further pulling the comets apart. 

The most striking example of this came shortly after the discovery of NEOWISE, with the observation of the fragmentation of the comet ATLAS in April this year. The collapse of this comet — believed at the time to offer our best look at such an icy body — in 30 separate pieces was also caught by Hubble. 

ATLAS feels the heat. The comet, discovered in December 2019 breaks up under the intense heat and gravitational influence of the Sun ( NASA/ ESA/ STScI/ D. Jewitt (UCLA))
ATLAS feels the heat. The comet, discovered in December 2019 breaks up under the intense heat and gravitational influence of the Sun ( NASA/ ESA/ STScI/ D. Jewitt (UCLA))

Unlike comet ATLAS, itself only discovered in December 2019, comet NEOWISE somehow survived its close passage to the Sun–with its solid, icy nucleus able to withstand the blistering heat of the star– enabling Hubble to capture the comet in an intact state.

As the latest image of NEOWISE shows, however, it is not going to escape its encounter with the Sun completely unscathed. Jets can clearly be seen blasting out in opposite directions from the poles of the comet’s icy nucleus. These jets represent material being sublimated–turning straight from a solid to a gas skipping a liquid stage–beneath the surface of the comet. This ultimately results in cones of gas and dust erupting from the comet, broadening out as the move away from the main body, forming an almost fan-like shape.

This animation composed of three Hubble images of NEOWISE shows clearly jets of sublimated material erupting from the comet forming fan-like shapes. (NASA, ESA, Q. Zhang (California Institute of Technology), A. Pagan (STScI), and M. Kornmesser))

Far from being just a stunning image of a comet as it passes through the inner solar system, the Hubble images stand to teach astronomers much about NEOWISE and about comets in general.

“It’s a fairly large comet that approached closer to the Sun than the vast majority of comets of its size do,” Zhangs says. “These factors contributed to its high brightness and also made it a good candidate to see how solar heating alters comets, as the effects are theoretically amplified by its close approach to the Sun.

“That information is useful for interpreting observed characteristics of other comets that don’t approach as close to the Sun, and thus where the changes are more gradual and might not be directly observable.”

In particular, the colour of the comet’s dust halo, and the way it changes as NEOWISE moves away from the Sun, gives researchers a hint as to the effect of heat on such materials. This could, in-turn, help better determine the properties of the dust and gas that form what is known as the ‘coma’ around a comet.

“We took images to show the colour and polarization of the dust released by the comet, to get a sense of what it looks like before it’s broken down by sunlight,” says Zhang. “That analysis is ongoing–and will take a while to do properly–but as the published images show, we’ve caught at least a couple of jets carrying dust out from the rotating nucleus.”

The information contained in the Hubble data will become clearer as researchers delve deeper into it. But, the investigation of NEOWISE’s cometary counterparts will benefit from future telescope technological breakthroughs. This will include spotting comets much more quickly and thus, further out from the Sun.

“When this comet was discovered by the NEOWISE mission, it was only 3 months from its close approach to the Sun and had already begun ramping up activity,” Zhang says. “More sensitive surveys, like the upcoming Legacy Survey of Space and Time (LSST) at the Rubin Observatory, will allow us to find such comets much earlier before they become active, enabling us to track them throughout their apparition from beginning to end.

“This will facilitate a more precise comparison of what changes the comets undergo during their solar encounter.”

The next step in Zhang’s research, however, will be comparing the qualities of comet NEOWISE to other such objects, particularly a recent interstellar visitor to our solar system: “This is one of three comets I have observed or have planned to observe in this manner, the others being the interstellar comet 2I/Borisov and the distant solar system comet C/2017 K2 (PANSTARRS),” the researcher concludes. “My team of collaborators and I will be evaluating all three comets to see how their differences in present location and formation/dynamical history translate into differences in physical properties.”

This artist's conception illustrates a Jupiter-like planet alone in the dark of space, floating freely without a parent star. (NASA)

Rogue Planets Could Outnumber Stars in the Milky Way

Our galaxy is teeming with rogue planets either torn from their parent stars by chaotic conditions or born separate from a star. These orphan planets could be discovered en masse by an outcoming NASA project — Nancy Grace Roman Space Telescope. 

The Milky Way is home to a multitude of lonely drifting objects, galactic orphans — with a mass similar to that of a planet — separated from a parent star. These nomad planets freely drift through galaxies alone, thus challenging the commonly accepted image of planets orbiting a parent star. ‘Rogue planets’ could, in fact, outnumber stars in our galaxy, a new study published in the Astronomical Journal indicates. 

“Think about how crazy it is that there could be an Earth, a Mars, or a Jupiter floating all alone through the galaxy. You would have a perfect view of the night sky but stuck in an eternal night,” lead author of the study, Samson Johnson, an astronomy graduate student at The Ohio State University, tells ZME Science. “Although these planets could not host life, it is quite a place to travel to with your imagination. The possibility of rogue planets in our galaxy had not occurred to me until coming to Ohio State.”

This artist’s conception illustrates a Jupiter-like planet alone in the dark of space, floating freely without a parent star. (NASA)

Up to now, very few very of these orphan planets have actually been spotted by astronomers, but the authors’ simulations suggest that with the upcoming launch of NASA’s Nancy Grace Roman Space Telescope in the mid-2020s, this situation could change. Maybe, drastically so.

“We performed simulations of the upcoming Nancy Grace Roman Space Telescope (Roman) Galactic Exoplanet Survey to determine how sensitive it is to microlensing events caused by rogue planets,” Johnson says. “Roman will be good at detecting microlensing events from any type of ‘lens’ — whether it be a star or something else — because it has a large field of view and a high observational cadence.”

The team’s simulations showed that Roman could spot hundreds of these mysterious rogue planets, in the process, helping researchers identify how they came to wander the galaxy alone and indicating how great this population could be in the wider Universe.

Rogue by Name, Rogue by Nature: Mysterious and Missing

Thus far, much mystery surrounds the process that sees these planets freed from orbit around a star. The main two competing theories suggest that these stars either are thrown free of their parent star, or form in isolation. Each process would likely lead to rogue planets with radically different qualities. 

ESO’s New Technology Telescope at the La Silla Observatory captures the rogue planet CFBDSIR J214947.2-040308.9 in infrared light–appearing as a faint blue dot near the centre of the picture. This is the closest such object to the Solar System discovered thus far. (ESO/P. Delorme)

“The first idea suggests that rogue planets form like planets in the Solar System, condensing from the protoplanetary disk that accompanies stars when they are born,” Johnson explains. “But as the evolution of planetary systems can be chaotic and messy, members can be ejected from the system leading to most likely rogue planets with masses similar to Mars or Earth.”

 Johnson goes on to offer an alternative method of rogue planet formation that would see them form in isolation, similar to stars that form from giant collapsing gas clouds. “This formation process would likely produce objects with masses similar to Jupiter, roughly a few hundred times that of the Earth.”

“This likely can’t produce very low-mass planets — similar to the mass of the Earth. These almost certainly formed via the former process,” adds co-author Scott Gaudi, a professor of astronomy and distinguished university scholar at Ohio State. “The universe could be teeming with rogue planets and we wouldn’t even know it.”

The question is if these objects are so common, why have we spotted so few of them? “The difficulty with detecting rogue planets is that they emit essentially no light,” Gaudi explains. “Since detecting light from an object is the main tool astronomers use to find objects, rogue planets have been elusive.”

Astronomers can use a method called gravitational microlensing to spot rogue planets, but this method isn’t without its challenges, as Gaudi elucidates:

“Microlensing events are both unpredictable and exceedingly rare, and so one must monitor hundreds of millions of stars nearly continuously to detect these events,” the researcher tells ZME Science. “This requires looking at very dense stellar fields, such as those near the centre of our galaxy. It also requires a relatively large field of view.”

Additionally, as the centre of the Milky Way is highly obscured by requiring us to look at it in the near-infrared region of the electromagnetic spectrum — a task that is extremely difficult as the Earth’s atmosphere makes the sky extremely bright in near-infrared light.

“All of these points argue for a space-based, high angular resolution, wide-field, near-infrared telescope,” says Gaudi. “That’s where Roman — formally the Wide Field InfraRed Survey Telescope (WFIRST) — comes in.” 

Nancy Grace Roman Space Telescope (and Einstein) to the Rescue!

The Roman telescope — named after Nancy Grace Roman, NASA’s first chief astronomer, who paved the way for space telescopes focused on the broader universe–will launch in the mid-2020s. It is set to become the first telescope that will attempt a census of rogue planets — focusing on planets in the Milky Way, between our sun and the centre of our galaxy, thus, covering some 24,000 light-years.

An artist’s redition of the Nancy Grace Roman Space Telescope, named after ‘the Mother of Hubble’ (NASA)

The team’s study consisted of simulations created to discover just how sensitive the Roman telescope could be to the microlensing events that indicate the presence of rogue planets, finding in the process, that the next generation space telescope was 10 times as sensitive as current Earth-based telescopes. This difference in sensitivity came as a surprise to the researchers themselves. “Determining just how sensitive Roman is was a real shock,” Johnson says. “It might even be able to tell us about moons that are ejected from planetary systems! We also, found a new ‘microlensing degeneracy’ in the process of the study — the subject another paper that will be coming out shortly.”

Johnson’s co-author Gaudi echoes this surprise. “I was surprised that Roman was sensitive to rogue planets with mass as low as that of Mars and that the signals were so strong,” the researcher adds. “I did not expect that before we started the simulations.”

The phenomenon that Roman will exploit to make its observations stems from a prediction made in Einstein’s theory of general relativity, that suggests that objects with mass ‘warp’ the fabric of space around them. The most common analogy used to explain this phenomenon is ‘dents’ created in a stretched rubber sheet by placing objects of varying mass upon it. The heavier the object — thus the greater the mass — the larger the dent. 

This warping of space isn’t just responsible for the orbits of planets, it also curves the paths of light rays, the straight paths curving as they pass the ‘dents’ in space. This means that light from a background source is bent by the effect of the mass of a foreground object. The effect has recently been used to spot a distant Milky Way ‘look alike’. But in that case, and in the case of many gravitational lensing events, the intervening object was a galaxy, not a rogue planet, and thus was a much less subtle, more long-lasting, and thus less hard to detect effect than ‘microlensing’ caused by a rogue planet. 

This animation shows how gravitational microlensing can reveal island worlds. When an unseen rogue planet passes in front of a more distant star from our vantage point, light from the star bends as it passes through the warped space-time around the planet. The planet acts as a cosmic magnifying glass, amplifying the brightness of the background star. (NASA’s Goddard Space Flight Center/CI Lab)

“Essentially, a microlensing event happens when a foreground object — in this case, a rogue planet — comes into very close alignment with a background star. The gravity of the foreground object focuses light from the background star, causing it to be magnified,” Gaudi says. “The magnification increases as the foreground object comes into alignment with the background star, and then decreases as the foreground object moves away from the background star.”

As Johnson points out, microlensing is an important and exciting way to study exoplanets — planets outside the solar system — but when coupled with Roman, it becomes key to spotting planetary orphans.

“Roman really is our best bet to find these objects. The next best thing would be Roman 2.0 — with a larger field of view and higher cadence,” the researcher tells ZME, stating that rogue planets are just part of the bigger picture that this forthcoming space-based telescope could allow us to see. “I’m hoping to do as much work with Roman as possible. The next big project is determining what Roman will be able to teach us about the frequency of Earth-analogs — Earth-mass planets in the habitable zones of Sun-like stars.”

Original Research

Johnson. S. A., Penny. M, Gaudi. B. S, et al, ‘Predictions of the Nancy Grace Roman Space Telescope Galactic Exoplanet Survey. II. Free-floating Planet Detection Rates*,’ The Astronomical Journal, [2020]. 

How a broken cable almost destroyed a thousand-foot telescope

The Arecibo Observatory in Puerto Rico, one of the largest radio telescopes in the world, was severely damaged during a tropical storm, with problems starting from a broken cable.

This is just the latest in a string of recent misfortune that the telescope suffered in recent years.

A photo of the damages. Credit University of Central Florida

One of the auxiliary cables that helps support a metal platform in place above the observatory broke on August 10, triggering a 100-foot-long gash on the telescope’s reflector dish. The damage happened during the Tropical Storm Isaias, but it isn’t clear yet just how the damage occurred.

“We have a team of experts assessing the situation,” said Francisco Cordova, the director of the observatory, in a statement. “Our focus is assuring the safety of our staff, protecting the facilities and equipment, and restoring the facility to full operations as soon as possible.”

The break occurred early in the morning when the storm was kicking in, according to Cordova. When the three-inch cable fell it also damaged about six to eight panels in the Gregorian Dome and twisted the platform used to access the dome. The observatory is now closed pending an investigation.

The observatory is managed by the University of Central Florida and it began operating in 1963. Over the years, it has produced many scientific discoveries in the solar system and beyond, being considered one of the most powerful telescopes in the world at the time. It’s also where SETI, the search of extraterrestrial intelligence, began. Nowadays, Arecibo is used by scientists around the world to conduct research in the areas of atmospheric sciences, planetary sciences, radio astronomy and radar astronomy. It is also home to a team that runs the Planetary Radar Project supported by NASA’s Near-Earth Object Observations Program.

While the damage was shocking to everyone, it’s far from the first time that Arecibo had to deal with technical difficulties. Back in September 2017, Puerto Rico was severely hit by Hurricane Maria, which knocked power across the island for months. An antenna suspended over the observatory fell and punctured a dish. The hurricane came at a difficult time for the observatory. The National Science Foundation, which owns Arecibo, was already considering giving the observatory to someone else so it could focus on other projects. The foundation finally did an agreement with a group of three institutions to take over the operations.

Then, earthquakes hit the island in January of this year. The tremors were as strong as 6.4 magnitudes and it made it impossible to carry out observations, with no visitors allowed on-site. The dish wasn’t damaged but operations couldn’t be restarted until the tremors fully stopped.

Using ALMA astronomers have revealed an extremely distant galaxy that looks surprisingly like our Milky Way. The galaxy, SPT0418-47, is gravitationally lensed by a nearby galaxy, appearing in the sky as a near-perfect ring of light. (ALMA (ESO/NAOJ/NRAO), Rizzo et al.)

Distant ‘Milky Way Look-Alike’ Challenges Theories of Galaxy Formation

Using the phenomenon of gravitational lensing astronomers have examined an extremely distant galaxy that shares many features with the Milky Way. The discovery of a calm galaxy so early in the Universe’s history calls into question our theories of how galaxies form. 

Using ALMA astronomers have revealed an extremely distant galaxy that looks surprisingly like our Milky Way. The galaxy, SPT0418-47, is gravitationally lensed by a nearby galaxy, appearing in the sky as a near-perfect ring of light. (ALMA (ESO/NAOJ/NRAO), Rizzo et al.)
Astronomers using ALMA, in which the ESO is a partner, have revealed an extremely distant galaxy that looks surprisingly like our Milky Way. The galaxy, SPT0418-47, is gravitationally lensed by a nearby galaxy, appearing in the sky as a near-perfect ring of light.
(ALMA (ESO/NAOJ/NRAO), Rizzo et al.)

Astronomers have discovered that a distant young galaxy that existed in the very early universe shares some surprising similarities with our galaxy. The fact that the young galaxy named SPT-S J041839–4751.9 or SPT0418–47 for short — located 12 billion light-years from Earth — resembles the Milky Way and the galaxies that surround it presents something of a problem. Galaxies that existed 1.4 billion years after the Big Bang, weren’t supposed to be so calm, unchaotic, and well-formed.

Thus the discovery of this throws many of our theories of galactic evolution into question. In fact, this finding fits into a series of recent discoveries that suggest galaxies began forming much earlier in the Universe’s history than previously believed. 

The research team reconstructed the distant galaxy’s true shape, shown here, and the motion of its gas from the ALMA data using a new computer modelling technique. 
(ALMA (ESO/NAOJ/NRAO), Rizzo et al.)

“This result represents a breakthrough in the field of galaxy formation, showing that the structures that we observe in nearby spiral galaxies and in our Milky Way were already in place 12 billion years ago,” says Francesca Rizzo, a PhD student from the Max Planck Institute for Astrophysics in Germany, and the lead author of a paper detailing the findings published today in the journal Nature

Whilst the observation of this distant galaxy would not have been possible without the impressive technology of the ESO’s Atacama Large Millimeter/submillimeter Array (ALMA) located in the Chilean Andes, it also hinged on the invention of another galaxy, and an extraordinary feature of Einstein’s theory of general relativity. The team reconstructed the accurate image of SPT0418–47 from the ring-like image received by ALMA as a result of gravitational lensing by an intervening galaxy. 

“We have studied in great detail a very distant galaxy. This means going back in time and we see this galaxy when it was very young, 1.4 billion years after the Big Bang,” Rizzo’s co-author, Filippo Fraternali, from the Kapteyn Astronomical Institute, the University of Groningen, Netherlands, tells ZME Science referring to the fact that the light from SPT0418–47 has travelled 12 billion years to reach us.

“Given that galaxies cannot form right after the Big Bang, we can estimate that SPT0418–47 [as we see it] is about 1-billion-years old.”

A Distant Milky Way Doppelganger With Some Key Differences

SPT0418–47 possesses a central bulge and a rotating disc, two features also displayed by the Milky Way and other local galaxies. However, it lacks the Milky Way’s spiral arms and is also much smaller than our home galaxy. This is the first time that astronomers have spotted a central bulge — stars tightly clustered around the galactic centre — in such a distant, and therefore early, galaxy. 

However, Fraternali notes that just because SPT0418–47 resembles the Milky Way at the stage we see it at, that doesn’t mean it evolved just as our galaxy did. “It is important to remark that whilst SPT0418–47 is similar to the Milky Way now, it does not mean that 12 billion years ago the Milky Way looked like SPT0418–47,” the researcher adds.

“In fact, we think that SPT0418–47 will evolve into a galaxy very different from the Milky Way, an elliptical galaxy, much more massive and without gas.”

How Astronomers Reconstructed SPT0418-47 (ALMA (NRAO/ESO/NAOJ)/Martin Kornmesser (ESO)/ Robert Lea)
How Astronomers Reconstructed SPT0418-47 (ALMA (NRAO/ESO/NAOJ)/Martin Kornmesser (ESO)/ Robert Lea)

Another key difference between the two galaxies is that SPT0418–47 is forming stars much more rapidly, unusual for a rotating disk. “SPT-S J041839–4751.9 belongs to a particular population of galaxies that are known as dusty star-forming galaxies,” Simona Vegetti, another co-author on the paper and an expert in gravitational lensing from the Max Planck Institute for Astrophysics, tells ZME Science. “As the name suggests, these are galaxies that are undergoing a significant burst of high-rate star formation.”

Vegetti goes on to explain that astronomers believe that as they age, galaxies like SPT0418-47 will turn into what is referred to as early-type galaxies — a galaxy which has consumed most of its gas and is not forming stars anymore.

“By comparing the properties of SPT-S J041839–4751.9 with those of nearby early-type galaxies, we can learn something about the processes which are responsible for the transformation from one galaxy type to the other,” shes says. “It’s a bit like comparing the properties of young and old people, it gives us some hints on the ageing process.”

But the most puzzling aspect of the distant galaxy is how calm and ordered it appears. Something current cosmological models cannot account for. 

Young and Chaotic? 

Our current cosmological models suggest that the Universe that SPT0418–47 as we see it inhabited was a chaotic and turbulent place. And galaxies found during this epoch are expected to reflect these qualities, even if they do possess some structure, this should be washed out by the violent conditions around them. 

“The general idea was that galaxies at those distances/times were extremely chaotic and one would barely recognise a disc in formation in amongst massive filaments of infalling gas and powerful explosions due to the extremely intense star formation,” says Fraternali. 

Galaxies in the early universe are expected to be the site of powerful phenomena like supernova explosions which release a lot of energy Vegetti explains, adding: “We would expect SPT-S J041839–4751.9 to be very turbulent, or in other words, we expect the motion of gas in this galaxy to move chaotically in winds and outflows.”

But the team’s observations reveal a completely different picture. What they actually found was that the motion of the gas in SPT0418–47 is, in fact, rotating around the centre of the galaxy quietly and in a well-ordered fashion. As Vegetti notes: “It is very hard to explain this behaviour within the context of the latest state-of-the-art numerical simulations of galaxies.”

ALMA (ESO/NAOJ/NRAO), Rizzo et al.

One of the man questions that remain for Fraternali is how common are these features and the relatively ‘calmness’ of SPT0418–47 in other older galaxies? “Because the galaxy has not been selected by us — it was, by chance, perfectly aligned with the lens along the line of sight — we may argue that it could be representative of a large fraction of massive galaxies at that time.”

Thus, staring back in time to conduct further investigation of these distant stars is of vital importance. But, that, as you may imagine, is no easy task. In fact, the study of SPT0418–47, as Fraternali indicates, was only made possible by the intervention of another galaxy coming between it and us, and the ensuing remarkable phenomena of gravitational lensing. 

Galaxies as Lenses — the Power of Gravitational Lensing

The exact alignment of SPT0418–47 and an intervening galaxy means that it appears as a near-perfect ring to the team at ALMA — a structure referred to by astronomers as an ‘Einstein ring’ by astronomers due to its connection to the theory of general relativity — the geometrical theory of gravity put forward by Einstein in the early years of the 20th Century. 

Gravitational lensing hinges on the fact that objects with mass curve the fabric of spacetime around them. The greater the mass, the more extreme the curvature. The most common analogy used to describe this is a stretched rubber-sheet having objects of increasing mass placed on it. A bowling ball creating a greater ‘dent’ on the sheet than a marble or a tennis ball. 

This means that an object like a galaxy with tremendous mass curves the path of light travelling past it, often this results in an object behind the lens appearing to be located in a different place. In extreme cases, creating an ‘Einstein Ring’ built up of light that took different curved paths around the intervening galaxy and thus arrived at Earth at slightly different times. But, isn’t just a beautiful and curious phenomenon of gravity, it’s also a powerful observational tool.  

ight from a distant galaxy is distorted by the gravitational effects of a foreground galaxy, which acts like a lens and makes the distant source appear distorted, but magnified, forming characteristic rings of light, known as Einstein rings. This effect has allowed astronomers to see the distant galaxy SPT0418-47 (which appears as a golden ring in the ALMA images) in finer detail than would have been possible otherwise. The foreground galaxy is not visible in the ALMA images of SPT0418-47 because it is too faint at the wavelengths used. The blue colour used in this schematic to represent this foreground galaxy is artificial. Credit: ALMA (NRAO/ESO/NAOJ)/Luis Calçada (ESO)
Light from a distant galaxy is distorted by the gravitational effects of a foreground galaxy, which acts like a lens and makes the distant source appear distorted, but magnified, forming characteristic rings of light, known as Einstein rings. This effect has allowed astronomers to see the distant galaxy SPT0418-47 (which appears as a golden ring in the ALMA images) in finer detail than would have been possible otherwise. The foreground galaxy is not visible in the ALMA images of SPT0418-47 because it is too faint at the wavelengths used. The blue colour used in this schematic to represent this foreground galaxy is artificial. Credit: ALMA (NRAO/ESO/NAOJ)/Luis Calçada (ESO)

“Because these galaxies are very far, it is challenging to study them in great detail using current telescopes, they are not powerful enough,” Vegetti says. “Our team then uses the effect of strong gravitational lensing to overcome this limitation.”

The process used by the team first involves the search for a pair of galaxies that are far away from each other but appear aligned from our vantage point here on Earth. “The galaxy closer to us will then behave like a lens providing us with a magnified view of the more distant galaxy,” Vegetti elaborates. “It’s like observing through a much more powerful telescope. 

“When we started studying this object we had no idea of what we were going to find. There are almost no other studies of galaxies so young at such a level of detail.”

Vegetti explains that the next generation of telescopes such as the James Webb Space Telescope and the ESO’s Extremely Large Telescope (ELT) should allow for the study of SPT0418–47 galactic contemporaries in much greater detail. This will allow researchers to discover just how common these features are, and in turn, possibly spark a rethink of how early well-ordered galaxies could form in the Universe’s history. She also reserves special praise for this study’s lead author.

“These new facilities will bring this type of analysis to the next level, allowing us to observe even younger galaxies with an even greater level of detail,” Vegetti concludes. “Francesca Rizzo is leading the way in this line of research. She is a brilliant young scientist with whom I enjoy working, so I am looking forward to our next discovery!”

Source

Rizzo. F., Vegetti. S., Powell. D., Fraternali. F., et al, ‘A dynamically cold disk galaxy in the early Universe,’ Nature, [2020].

This is the best place in the world to see the cosmos at night — if you can bear it

The Dome A, the highest ice dome on the Antarctic Plateau, is the best place on the planet to study the stars, providing the clearest views of the sky at night, according to new research, which will probably trigger the interest of astronomers ready to cope with the Antarctic cold weather.

Credit Flickr

Ice domes are the uppermost portions of ice sheets and rise high above the frozen terrain. The Dome A is considered one of the coldest places on Earth, with temperatures that can be as low as -90ºC (-130 Fahrenheit). That’s actually similar to the nighttime weather found on Mars.

That means that while it may be a great place for astronomers, its remote location and extreme conditions present significant challenges. Scientists that want to visit the Dome A would have to travel 1,200 kilometers (740 miles) into the interior of the Antarctic continent — and that’s after traveling to Antarctica itself.

“The combination of high altitude, low temperature, long periods of continuous darkness, and an exceptionally stable atmosphere, makes Dome A a very attractive location for optical and infrared astronomy. A telescope located there would have sharper images and could detect fainter objects,” said Paul Hickson, co-author of the study, in a press release.

For astronomers, light pollution isn’t just the only problem when looking at the night sky. Atmospheric turbulence can also affect clear views into space. That’s when the telescopes located at mid and high elevations become very useful, taking advantage of the weaker turbulence found at those locations.

Astronomers calculate the quality of the night sky view using a metric called the seeing number, which they measure in arcseconds. The lower the number, the lower the turbulence and the better the view they can get from the stars and the galaxies. In the elevated telescopes in Chile and Hawaii, the seeing number is 0.6 to 0.8 arcseconds.

At Dome C, which is another dome on the Antarctic Plateau, the number is between 0.23 and 0.36 arcseconds. This means that the continent is an ideal place to watch the night sky. The level of turbulence there is lower as the boundary layer, the lowest part of the Earth’s atmosphere.

Working with researchers from China, Canada, and Australia, Hickson showed in his study that the Dome A is actually better than the Dome C. They took nighttime measurements at that location, something that hadn’t been done before, and found out that the median seeing number was 0.31 arcseconds.

The researchers compared the two Antarctic sites and found that the measurements from Dome A at eight meters (26 feet) were much better than the ones taken at the same height at Dome C. The measurements from Dome A at this height were equivalent to the ones made at 20 meters (66 feet) at Dome C.

Dome A “is a natural laboratory for studies of the formation and dissipation of turbulence within the boundary layer,” wrote the authors in their paper. “Future measurements of weather, seeing and the low-altitude turbulence profile could contribute to a better understanding of the Antarctic atmosphere.”

The study was published in the journal Nature.

Do Black Holes Merge? (NASA/Public Domain)

Double Trouble! Hunting for Supermassive Black Hole Mergers

Supermassive black holes sat at the centre of active galaxies could have company. Binary pairs of these titanic cosmic objects could merge to form an even more monstrous black hole. Observational methods are finally becoming sensitive enough to spot such an event. 

The image of a supermassive black hole sat monolithic and alone at the centre of its galaxy, mercilessly swallowing any matter unfortunately enough to cross its path could be seriously challenged over the coming years. Theories of how galaxies grow and evolve and the role supermassive black holes play in these processes have long suggested that these objects may not dwell alone. In fact, not only may such spacetime events live in pairs, but after being brought together, they may merge in what could be the most powerful single event in the Universe, profoundly affecting its evolution.

Do Black Holes Merge? (NASA/Public Domain)
Artist’s impression of a violent merger between two supermassive black holes (NASA/ Pubic Domain)

“Astrophysical black holes are among the most fascinating objects in the Universe: they are ideal laboratories to study the fundamental laws of physics and one of the main drivers of the evolution of the Universe,” explains Alessandra De Rosa, a research astrophysicist at the National Institute of Astrophysics, Roma, Italy. “Understanding how they work and interact with their close environment, and unveil the physical conditions of the medium around them is one of the major challenges of 21st-century Astrophysics.”

Understanding the relationship between black holes and the galaxies that host them is key to building a model that satisfactorily describes the evolution of both. But, thus far evidence of this process is sparse. So, why are supermassive black hole mergers so hard to spot?

Hidden in Plain Sight. How Supermassive Black Hole Binaries and Mergers evade Observation

Despite the potential power of such a merger event, we haven’t as of yet managed to distinguish individual binary supermassive black holes or much evidence that such collisions occur. This is because these pairings and the mergers that may eventually arise from them lurk in what is known as the Active Galactic Nuclei (AGN) — compact regions at the centre of galaxies where the electromagnetic emissions dwarf that of the entire galaxy which surrounds it.

Because this emission — which occurs from the radio wave to the gamma-ray regions of the electromagnetic spectrum — is so powerful, astronomers believe that it does not arise as a result of stellar activity. Rather, they theorise that the powerful electromagnetic radiation emitted by the AGN is the result of at least one supermassive black hole accreting matter — a violent process in which dust, gas, and even stars are ripped apart in a violent and tremendously hot accretion disc surrounding a central supermassive black hole before falling onto what can roughly be described as its ‘surface.’

Here’s the problem; that electromagnetic emission is so overwhelmingly powerful and the AGN is so small in comparion to its host galaxy that there is no way that traditional astronomy — which relies on electromagnetic signals — alone, can distinguish the finer detail of this region. Finer detail that could reveal occupation by two, rather than just one, supermassive black holes.

“Currently, observational evidence for these pairs is almost non-existent,” De Rosa laments. “This can be explained if they quickly shrink to small separations and become impossible to be resolved with telescopes as pairs. So,  we must rely on indirect signatures.”

Fortunately, supermassive black hole mergers, if they occur, would not just be prodigious producers of electromagnetic radiation. They should also produce intense gravitational wave signals.

De Rosa is the lead author of a review paper published in the journal New Astronomy Reviews that looks both the history of our search for supermassive black hole binaries and puts forward a road map for future discovery of such events. The researcher emphasises the importance of ‘multimessenger astronomy’ — which combines traditional electromagnetic observations with the detection of gravitational waves, allowing astronomers to view the Universe in an entirely new way, thus making events and objects are previously hidden to them — events like black hole mergers — accessible.

But before examing mergers, it’s worth considering the truly epic processes that bring supermassive black hole pairings together in the first place.

Cosmic Matchmaking: Bringing Together Supermassive Black Holes

It may not be too surprising to find supermassive black holes hanging-out together in pairs, as our observations of the Universe thus far, show that stellar objects seem to prefer to hang out in pairs. These binary systems are far more common than single star systems such as our solar system, and three-star systems — the latter of which prove to be far too unstable.

“A binary supermassive black hole is made up of two supermassive black holes that are orbiting around each other,” says Julie Comerford, an Associate Professor in the Department of Astrophysical and Planetary Sciences at the University of Colorado, Boulder who specializes in the study of AGNs. “Such binary systems are common in the universe — around half of all stars are in binary systems, where two stars are orbiting around each other.”

As black holes evolve from such stellar objects, and these objects enjoy the company, it would seem intuitive to believe that black hole binaries should be fairly common. There’s a problem with that thinking though.

Only the most massive stars end their lives as black holes, and supermassive black holes are even rarer. Couple that with the fact that most binary systems contain a massive star coupled with a much smaller counterpart. Thus, It’s quite unlikely that two stars in the same binary system would both end up as supermassive black holes. In fact, after the transformation of the first star, it’s likely its partner will be stripped of material and left as a neutron star, a much smaller white dwarf, or destroyed entirely– possibly consumed by its counterpart.

So, if supermassive binaries aren’t likely to grow together, this means that some event must create this union– the merger of two galaxies.

“Each massive galaxy has a supermassive black hole at its centre, so the way you make a supermassive black hole binary is by merging two galaxies together,” Comerford tells ZME Science. “Each galaxy brings its own supermassive black hole to the merger, and as the galaxies combine the supermassive black holes begin their own dance of orbiting around each other.”

This means that spotting such a supermassive black hole binary would provide good evidence that the galaxy it occupies is the result of a merger, or even, that such a merger is still ongoing. It would also give us a hint at what is to come for our own galaxy. “This will one day happen to our Milky Way Galaxy — when it merges with the Andromeda Galaxy in about 4 billion years,” Comerford continues. “Our supermassive black hole and Andromeda’s supermassive black hole will form a binary!”

Mathematical modelling of these galaxy mergers seems to show that the process causes major gas inflow towards the central supermassive black hole — or black holes, as the case may be — this powers accretion and various nuclear processes activating the galactic nucleus. This inflow of gas, dust and other material could also result in the growth of the supermassive black hole.

“Astronomers believe that galaxies merge one or more times during their cosmological life,” says Alessandra De Rosa, who is is a research astrophysicist at the National Institute of Astrophysics, Roma, Italy. “These gigantic collisions are likely to be the primary process by which supermassive black holes are activated.”

Thus, galactic mergers aren’t just responsible for bringing supermassive black holes together, they also could kick start the feeding frenzy that makes an AGN the source of incredibly powerful radiation.

But what happens when these binary pairs of supermassive black holes form? Do they remain in a binary, or do they combine to form an even larger supermassive black hole? The merger of supermassive black holes to form larger objects would explain certainly one lingering cosmological question; how did these objects grow to such tremendous sizes in such a short period of time?

Despite the convenience of this phenomenon to tie up some loose cosmic-ends, we still don’t really know if it’s happening or not.

Using Gravitational Waves to Shed Light on Black Hole Binaries

After being brought together by a galaxy merger, when the supermassive black holes are very small separations, the gravitational waves that they emit carry away energy and enable the black holes to merge.

Thus, supermassive black holes at the centre of each galaxy are dragged close to each other, and eventually, form what is known as a dual active galactic nucleus. Theoretically, the final stage of this coming together — particularly if the black holes are gravitationally bound — will be the coalescence of these monsters in a merger that results in an even larger supermassive black hole. This merger would be accompanied by the emission of a gravitational-wave signal. Signals that thanks to the Laser Interferometer Gravitational-Wave Observatory LIGO, and its upcoming space-based counterpart Laser Interferometer Space Antenna (LISA), we can now theoretically detect.

“We think that binary supermassive black holes ultimately merge with each other and produce very energetic gravitational waves. In fact, supermassive black hole mergers are second only to the Big Bang as the most energetic phenomena in the Universe,” Comerford explains. The problem is, that even LIGO — responsible for the first detection of gravitational waves from colliding stellar-mass black holes — isn’t yet capable of detecting gravitational waves from merging supermassive black hole.

“These gravitational waves are too high frequency to be detected by LIGO, so they have not yet been detected,” Comerford adds. “But, we expect that pulsar timing arrays will detect gravitational waves from supermassive black hole mergers for the first time in just a few years.”

De Rosa concurs with the possible breakthrough in detecting gravitational waves from supermassive black hole mergers, highlighting not just the future contribution of pulsar timing arrays, but also, that of LISA — a space-based laser interferometer set to launch in 2034. “In the next decades, space-borne gravitational wave observatories, such as the next large mission of the European Space Agency, LISA, and experiments such as the Pulsar Timing Arrays, will provide first direct evidence of binary and merging SMBHs in the Universe,” she explains. 

For Comerford, the breakthrough new gravitational wave detection methods and multi-messenger astronomy stand poised to answer fundamental questions that have influenced her entire career. “When I was a graduate student, my group found some intriguing galaxy spectra that we thought might be produced by supermassive black hole pairs. I wondered if these unusual spectra could be the key to finding supermassive black hole binaries. I’ve been working on new and better ways to find supermassive black hole pairs ever since,” the researcher concludes. 

“I think the shocking thing is that we don’t actually know if supermassive black hole binaries merge! It could be that they just circle around each other and are not able to get close enough to each other where the gravitational waves can take over and make them merge. 

“When we detect gravitational waves from supermassive black holes, that will be the first time that we actually know that supermassive black hole binaries do merge.”


Sources and Further Reading 

De Rosa. A, Vignali. C, Bogdanovic. T, et al, ‘The Quest for Dual and Binary Supermassive Black Holes: A Multi-messenger View,” New Astronomy Reviews, [2020]. 

Aurora-like phenomenon spotted on Mars for the first time

The European Space Agency’s Trace Gas Orbiter (TGO) has just spotted a green light in the atmosphere of Mars — the first time such phenomenon is seen on a world beyond the Earth. This is different from the type of aurora we know as the Northern Lights.

A green band of oxygen glow is visible over Earth’s curve. Image ESA

Skywatchers on Earth have long enjoyed classic aurorae such as the Northern and Southern Lights. The glow is due to the collisions between atmospheric molecules and charged particles that are racing away from the Sun. The interaction is influenced by the Earth’s magnetic field, which pulls the particles to the poles.

But the night glow is different. It’s generated by the interaction of sunlight with oxygen atoms and molecules in the air. The emission is very difficult to see, even from Earth. That’s why the best images of the green night glow are usually taken by astronauts at the International Space Station (ISS):

“One of the brightest emissions seen on Earth stems from night glow. More specifically, from oxygen atoms emitting a particular wavelength of light that has never been seen around another planet,” study lead author Jean-Claude Gérard said in a statement. “This emission has been predicted to exist at Mars for around 40 years — and, thanks to TGO, we’ve found it,” Gérard said.

The emission was seen using a special observing mode of the TGO. One of the instruments available there, known as NOMAD, has an ultraviolet and visible spectrometer. This allows it to observe in different configurations – one of which positions its instruments to point directly down at Mars.

Co-author Ann Carine Vandaele, the chief investigator of NOMAD, said that despite many efforts they hadn’t been able to capture any green glow in the past. That’s why they decided to reorient their observations to the “edge of Mars,” which is similar to the photos seen of Earth taken from the ISS.

NOMAD was used between 24 April and 1 December 2019 to scan altitudes ranging from 20 to 400 kilometers above the Martian surface, twice per orbit. The green glow was seen in all the datasets observed by the researchers. The emission was strongest at an altitude of 80 kilometers and also varied based on the distance between Mars and the Sun.

The researchers wanted to understand better the green glow in Mars so they also modeled the phenomenon, finding out that it was produced mainly as a breakdown product of carbon dioxide (CO2). Sunlight frees one of the oxygen atoms in CO2, and it’s the transition of this atom that’s glowing green on the Red Planet.

“The observations at Mars agree with previous theoretical models but not with the actual glowing we’ve spotted around Earth, where the visible emission is far weaker. This suggests we have more to learn about how oxygen atoms behave, which is hugely important for our understanding of atomic and quantum physics,” said Gerard.

Observations of the green glow could help inform the models that guide the entry, descent and landing of Mars probes, the researchers hope. Atmospheric density, for example, directly affects the drag experienced by orbiting satellites and by the parachutes used to deliver probes to the martian surface. The Perseverance rover is expected to be launched this year from Florida’s Cape Canaveral Air Force Station.

Titan is moving away from Saturn 100 times faster than expected

Saturn’s moon Titan, an icy world shrouded by a hazy atmosphere, is the second-largest moon in our solar system, nearly 50% larger than the Earth’s moon.

In a new study published in Nature Astronomy, a team of researchers report that Titan may be straying from its planet at a much faster rate than anticipated.

Titan passing in front of Saturn — slowly drifting apart, bit by bit. Image credits: NASA / JPL.

Every moon slowly drifts away from its planet due to tidal forces. The orbiting moon exerts a gravitational pull on the planet as it orbits, creating a temporary bulge as it passes over — this is also the reason why we have high tides and low tides on Earth, for instance.

The planet’s spin sweeps the bulge forward ever so slightly, which in turn pulls on the moon and transfers it into a higher orbit. That way, the moon moves away from the planet ever so slightly each year.

So long, old friend

Previously, scientists had estimated the rate Titan moves away from Saturn to be around 0.1 cm per year. But according to recent data gathered by NASA’s Cassini spacecraft, Titan actually drifts away 100 times faster than expected, at a rate of approximately 11 centimeters each year.

These findings, while contradicting previous predictions, agree with a hypothesis proposed in 2016 by Jim Fuller, Jing Luan, and Eliot Quataert. The researchers proposed a mechanism also observed in binary stars called resonance locking, which could explain the fast migration seen in Saturn’s moon Titan. This is a process where the gravitational force of the moon squeezes the planet and forces it to oscillate. In this case, the orbital motion of Titan lines up with internal motions inside Saturn increasing the efficiency of the tidal forces and leading to a faster migration rate.

This finding also bears significant implications for the formation of Saturn’s rings and moon system (which hosts over 80 moons).

If the speed at which Titan is straying from Saturn is so large now, it implies that it was also larger in the past. This means that Titan, previously thought to have formed at a similar distance from its planet as where it is now, may have formed much closer to Saturn and then migrated outwards. This changes our understanding not only of how Saturn’s rings and moons formed but also interactions in binary star systems, galaxies, and exoplanets in close orbit to their stars.

Now, scientists await more data from the Juno space probe orbiting Jupiter which could validate the theory of resonance locking further.

CSIRO’s ASKAP telescope continues to detect new FRBs, adding to the catalogue of these mysterious objects. Credit: ICRAR and CSIRO/Alex Cherney

The Universe’s Missing Matter Problem is Solved

Our theories of the Universe have a missing matter problem: half of its matter is missing. But now this ‘missing baryon problem’ one of the most lingering puzzles in cosmology has been solved.

Analysis of the Cosmic Microwave Background (CMB), the radiation left over from an event that occurred shortly after the ‘Big Bang’ which evenly fills the entire Universe, tells physicists that ‘normal’ or baryonic matter  —  the stuff that forms planets, stars, and our bodies  — should account for roughly 5% of the total matter and energy in the Universe.

The problem has been that until now, roughly half of this baryonic matter (essentially the building blocks of everything we see around us )  has been missing.

Australian astronomers have used fast radio bursts, mysterious blasts of radio-wave radiation that occur in random directions through deep space, whose origins are as of yet unknown, to trace this missing matter for the first time. In the process, the discovery helps confirm that both theories of nucleosynthesis in the early Universe, and our concept of how the cosmos developed immediately following the Big Bang are correct. 

The team’s findings are published in the journal Nature. 

CSIRO’s ASKAP telescope continues to detect new FRBs, adding to the catalogue of these mysterious objects. Credit: ICRAR and CSIRO/Alex Cherney
CSIRO’s ASKAP telescope continues to detect new FRBs, adding to the catalogue of these mysterious objects. Credit: ICRAR and CSIRO/Alex Cherney

“The matter in this study is ‘ordinary’ matter — the material that makes up our bodies, the Earth, and the entirety of the periodic table. We refer to this matter as ‘baryonic’–matter made up of baryons like electron and protons,” says the paper’s co-author Professor J. Xavier Prochaska, UC Santa Cruz, says. The researcher adds that it’s worth noting that this matter isn’t ‘dark matter’ which accounts for roughly 85–90% of the Universe’s matter content.

The two-decade-long hunt for the missing baryonic matter

Thus far astronomers have spent at least two decades searching for this matter using a very precise estimate of the total mass of baryons in our Universe derived from an analysis of data from the early Universe. 

“The hunt for missing matter engaged astronomers across the globe over the past 20 years,” Prochaska explains. “An unofficial accounting estimates 1000+ orbits with the Hubble Space Telescope, thousands of hours with the Chandra X-ray Observatory, and 100+ nights on the largest optical telescopes; these total over $50M USD in operations alone.” 

Yet, despite this monumental effort, a successful census of all the matter in the Universe has not been carried out — until now. Current best measurements account for only around half the baryonic matter, leaving the other half effectively missing.

“When we looked out into the present Universe, we couldn’t find half of the matter that should be there,” says lead author, Associate Professor Jean-Pierre Macquart, Curtin University, International Centre for Radio Astronomy Research (ICRAR). “It was a bit of an embarrassment.”

The issue with finding this missing matter is primarily because it is extremely diffuse and space is extremely sparse. Macquart compares that searching for this matter to searching for just a few atoms in a room the size of the average office. The problem with this matter existing in such a diffuse and tenous gas is that it doesn’t emit light itself, and when background light passes through it, none is absorbed. 

Thus this missing matter doesn’t leave any ‘fingerprint’ and it is, for all practical purposes, invisible. This means that traditional telescopes and the techniques associated with them simply aren’t effective enough to spot such diffuse matter. 

The missing matter that the team of astronomers has located fits within the yellow slice of a pie chart showing the Universe's total energy andmatter content. It isn't dark matter, or dark energy, both of which remain 'missing.'

“The missing matter has a density and temperature that make it effectively invisible to any other technique used to observe it,” explains Prochaska. “Indeed, we have not imaged it either.”

“In a way, you can think of this as ‘grey matter’ in that, it isn’t dark matter,” Macquart explains. “It’s ordinary matter that we could see if it weren’t so diffuse.”

The team of astronomers, therefore, had to find another way to detect that matter. That means finding some other impact or effect that this matter could have, that could be spotted. This is where the phenomenon of Fast Radio Bursts (FRBs) comes in to play.  

Fast Radio Bursts as a detection method

The first Fast Radio Burst was detected in 2007 and since then these, seemingly random blasts of radiation lasting just a few milliseconds, have been recorded many times. This includes the observation in April this year, of the first FRB within our own galaxy, and the first regularly repeating FRB —named FRB 181112 —  in 2018.

Yet, the actual origins of these emissions and their causes are still unknown. 

The FRB leaves its host galaxy as a bright burst of radio waves. (ICRAR)
The FRB leaves its host galaxy as a bright burst of radio waves. (ICRAR)

Despite the mystery around their emission, researchers have still found a way to both localize their source to a host galaxy and to utilize FRBs to measure other phenomena in the Universe. Last year, Prochaska himself was part of research to investigate diffuse gas haloes using FRBs as a probe. The researcher says that from their very discovery by Duncan Lorimer and his student David Narkevic thirteen years ago, he believed that FRBs could be employed in the search for missing baryonic matter. 

“In 2007, I recall discussing Duncan Lorimer’s paper on the first fast radio burst — sometimes referred to as the ‘Lorimer Burst’ — the morning it published,” Prochaska says. “It hit me right then that this would be the best way to find the missing matter.”

To make the detection the team utilized two distinct methods, the dispersion measure and the redshift of the FRB’s origin galaxy. The dispersion measure allows researchers to count the number of encountered electrons as these slow the propagation of the FRB  — with different frequencies that make up the burst be affected to varying degrees.

Whilst, analysis of the spectrum yields the redshift which is effectively a measure of the distance to the FRB’s origin galaxy. This latter part is important because the researchers need to know just how much ‘space’ the FRB has traveled through. 

“Thus, combining redshift and dispersion measure, we can assess the total mass in baryons in the universe,” Prochaska explains. 

It’s all about timing…

FRBs can be used as a probe for baryonic matter because as they travel across the Universe, every atom they encounter slows them down by a tiny amount. This means that they carry with them a trace of every atom they encounter along their line of travel. Even those astronomers can’t see.

The tenous gas cloud that the FRB passes through consists of atoms that have been ionised, this means that the protons and electrons have been separated and float freely in the gas. 

The density of the missing matter is calculated using the distance of the FRB from Earth and the delay between the wavelengths of the FRB, (Credit: ICRAR)
The density of the missing matter is calculated using the distance of the FRB from
Earth and the delay between the wavelengths of the FRB, (Credit: ICRAR)

When radio waves pass through this ionised gas, the different frequencies that make up the FRB propagate at slightly different speeds. This means that the different frequencies which start off perfectly aligned become slightly spread out bt the time the FRB reaches the other side of the gas cloud. 

Macquart describes this phenomenon as exactly what we see when light passes through a prism.

This dispersion in timing is tiny but builds up over the vast distances travelled between galaxies, and the amount of dispersion is exactly proportional to the amount of ionised matter the radio pulse has passed by. 

When travelling through completely empty space, all wavelengths of
the FRB travel at the same speed, but when travelling through the missing matter, some wavelengths are slowed down. (Credit: ICRAR)
When travelling through completely empty space, all wavelengths of
the FRB travel at the same speed, but when travelling through the missing matter, some wavelengths are slowed down. (Credit: ICRAR)

Thus, when the team measure these FRBs they can calculate how smeared out in time the frequencies are, revealing just how much-ionised matter they had passed through on their journey to us. Once the distance of the origin galaxy from which the bursts originated is known, the astronomers could also then measure the average density of the ionised matter, and check this against theoretical predictions.

Leading the way with ASKAP

This combination of methods also required a combination of telescopes and techniques. To conduct their study the team of astronomers turned to CSIRO’s Australian Square Kilometre Array Pathfinder (ASKAP) — a radio telescope consisting of 36 12-inch antennas located roughly 500 miles north of Perth in Western Australia — and some of the world’s most powerful optical telescopes. Prochaska is clear here though: “ASKAP led the way.”

The team used ASKAP to measure the positions of the FRB and thus determine the galaxy from which they originated, unsurprising, as the instrument has become the foremost piece of technology in terms of localising FRBs. 

CSIRO’s ASKAP
measures the delay between the wavelengths of the FRB, allowing
astronomers to calculate the density of the missing matter (Credit: ICRAR and CSIRO/Alex Cherney)
CSIRO’s ASKAP measures the delay between the wavelengths of the FRB, allowing
astronomers to calculate the density of the missing matter (Credit: ICRAR and CSIRO/Alex Cherney)

ASKAP found the smeared-out bursts of radio emission, which gave the researchers two key pieces of information — how much ionised matter was between the source of the burst and us on Earth, and where to go looking for the galaxy that the burst had originated in. This is why ASKAP was key to the team, whilst other radio telescopes are able to localise FRBS, almost none of them can pinpoint the location of the burst precisely enough to determine which galaxy they came from.

“To ID an FRB we had to scour through weeks of data to find a single interesting measurement,” Dr Keith Bannister, an Astronomer at CSIRO explains. “Like a needle in a haystack the size of 100 football stadiums.” Fortunately, ASKAP has what Bannister calls a ‘live-action replay’ saving the last 3 billion measurements–just 3 seconds worth of data–from each antenna.

The ASKAP could only solve 2/3 of the missing baryon puzzle, however. Other telescopes were used to measure the redshift of these host galaxies, most incredibly distant and faint, with this measurement giving the team an estimate of the distance and the speed at which the expansion of the Universe is carrying it away. Once the FRB travel distance was known the team could calculate the density of all the atoms along the line of sight.

We know the missing matter is there, now we need to know where ‘there’ is

The idea of ‘finding’ this missing matter may be a touch misleading. The team are quick to point out, that even though they now are able to show that this matter is there, they are yet to determine exactly where it is and how it is distributed.

The next question they will aim to answer is whether this gas is evenly spread smoothly between galaxies, or if it is gathered in haloes and filaments?

Core antennas of CSIRO’s ASKAP radio telescope in Western Australia pointing at the Milky Way. (Credit: CSIRO/ Alex Cherney)
Core antennas of CSIRO’s ASKAP radio telescope in Western Australia pointing at the Milky Way. (Credit: CSIRO/ Alex Cherney)

“Of particular interest to astronomers is to ascertain the fraction of the material that is tightly bound to galaxies versus the fraction that is out in the open Universe — what we refer to as the intergalactic medium or cosmic web,” Prochaska says. But, for him in particular, this finding marks the end of a twenty-year journey. 

“I began this pursuit in 2000 as a postdoc at Carnegie Observatories,” Prochaska concludes. “Ten years after the discovery of Fast Radio Bursts as new radio experiments were tooling up to join the search, I formed a team called ‘Fast and Fortunate for FRB Follow-up’ ) to perform the follow-up with optical telescopes. 

“I never dreamed it would go this smoothly…”

References: Macquart. JP, Prochaska. J. X, McQuinn. M, et al, ‘A census of baryons in the Universe from localized fast radio bursts,’ Nature, [2020].

Scientists discover evidence of ancient rivers in Mars

Despite now being unhospitable, Mars’s surface was once covered in water in different forms, from rivers to even a huge ocean. Understanding the history behind the red planet and how it lost its water has long been a focus of researchers. Cutting-edge technology is now bringing them closer to that goal.

Credit Utrecht University

An international group of researchers used images and topography data captured by NASA’s Mars Reconnaissance Orbiter’s HiRISE camera to study a rim of the Hellas Basin in Mars’ southern hemisphere – which had long been of interest as it’s one of the largest in the solar system.

The team narrowed its focus to a rocky cliff roughly 656 feet high that’s about 3.7 billion years old that’s part of this basin. Composed of sediment accumulated over time, its rocks are like the rocks found on Earth’s rivers. The high-resolution images reveal that it was formed by rivers more than 3.7 billion years ago.

These exposed cliff faces on Mars reveal “rivers that continuously shifted their gullies, creating sandbanks, similar to the Rhine or the rivers that you can find in Northern Italy,” the researchers said in their study.

The sedimentary rocks record layers of history, and the researchers were able to determine that the channels of these ancient rivers were around 9 or 10 feet, or several meters, deep.

Analyzing these layers on Mars can shed more light on its history, much like geologists used sediment layers on Earth to understand how our planet evolved over time and envision what it was like millions and billions of years ago, the researchers argued.

William McMahon, co-lead author of the paper, said in a statement: “Here on Earth, sedimentary rocks have been used by geologists for generations to place constraints on what conditions were like on our planet millions or even billions of years ago. Now we have the technology to extend this methodology to another terrestrial planet.”

The rocks studied by the team can only tell us about a fraction of the time that water and sediment were being moved in the region because erosion erased whole layers of its geologic history. But other rocks acting as markers of time could yet be undiscovered or buried, they said.

Based on the evidence they found in the orbital data, the researchers believe that the planet’s water cycle was driven by precipitation, like the rain we experience on Earth, and that liquid water had a sustained presence 3.7 billion years ago.

“We’ve never seen an outcrop with this amount of detail on it that we can definitely say is so old. This is one more piece of the puzzle in the search for ancient life on Mars, providing novel insight into just how much water occupied these ancient landscapes,” Joel Davis, co-author, said in a statement.

In 2022, the European Space Agency (ESA) is due to launch the Rosalind Franklin ExoMars rover, which will explore similar terrains to determine whether there has ever been life on Mars and to better understand the history of water on the planet. The researchers will help to interpret the findings.

The findings were published in the journal Nature Communications.

Highest-ever resolution images of the sun revealed

The highest-ever resolution images of the sun have been unveiled by a group of British scientists working alongside NASA researchers, proving that the atmosphere of the sun is much more complex than we thought.

Credit University of Central Lancashire

Analyzed by researchers at the University of Central Lancashire (UCLan) and collaborators from NASA’s Marshall Space Flight Centre, the images will now provide astronomers with a better understanding of the sun’s atmosphere.

Scorching glory

The images were taken by NASA’s High-Resolution Coronal Imager (Hi-C) telescope, carried into space on a sub-orbital rocket flight. The telescope can pick out structures in the sun’s atmosphere as small as 70km in size, or about 0.01% of the star’s total size.

Until now, certain parts of the sun’s atmosphere appeared dark or mostly empty, but the new images revealed strands that are about 500 kilometers (260 miles) in width with hot electrified gases flowing inside them.

“Until now, solar astronomers have effectively been viewing our closest star in ‘standard definition’, whereas the exceptional quality of the data provided by the Hi-C telescope allows us to survey a patch of the sun in ‘ultra-high definition’ for the first time,” Robert Walsh, professor of solar physics at UCLan, said in a statement.

Hi-C is a bit different from most telescopes since it’s launched on a sub-orbital rocket. On its last flight in 2018, Hi-C spent about five minutes snapping images of the sun from the edge of space. It returned to Earth through a parachute-assisted landing.

The exact physical mechanism that is creating these pervasive hot strands remains unclear, so the scientific debate will now focus on why they are formed, and how their presence helps us understand the eruption of solar flares and solar storms that could affect life on Earth.

Credit University of Central Lancashire

The international team of researchers is now planning to launch the Hi-C rocket mission again, this time overlapping their observations with two sun-observing spacecraft currently gathering further data, NASA’s Parker Solar Probe and ESA’s Solar Orbiter (SolO).

Amy Winebarger, Hi-C investigator at NASA’s Marshall Space Flight Center, said: “These new Hi-C images give us a remarkable insight into the Sun’s atmosphere. Along with ongoing missions such as Probe and SolO, this fleet of space-based instruments in the near future will reveal the Sun’s dynamic outer layer in a completely new light.”

Tom Williams, a postdoctoral researcher at UCLan who worked on the Hi-C data, said in a statement that the images would help provide a greater understanding of how the Earth and sun-related to each other.

“This is a fascinating discovery that could better inform our understanding of the flow of energy through the layers of the sun and eventually down to Earth itself,” he said. “This is so important if we are to model and predict the behaviour of our life-giving star.”

The research has been published in the Astrophysical Journal.

Uranus is leaking gas — according to NASA

More than 30 years ago, NASA’s Voyager 2 spacecraft flew over Uranus, getting as close as 50,600 miles to the planet’s clouds.

The data collected back revealed new rings and moons. But there was another finding as well, which remained hidden for a long time.

Credit NASA

A team of researchers from NASA took a new look at the data from the spacecraft, discovering that the voyager had passed through a gigantic magnetic bubble, also called a plasmoid – a giant structure comprised of plasma and the planet’s magnetic field.

Space physicists Gina DiBraccio and Dan Gershman, both from NASA’s Goddard Space Flight Center, reviewed the Uranus data because they wanted to understand its strange behavior. “The structure, the way that it moves …,” DiBraccio said, “Uranus is really on its own.”

Unlike any other planet in our solar system, Uranus turns almost perfectly sideways, like a rolling barrel. This axis of rotation points in a direction 60 degrees apart from its axis of the magnetic field, making its magnetosphere wobble chaotically as it rotates.

The researchers downloaded the readings obtained by Voyager 2’s magnetometer, which monitored the strength and direction of Uranus’ magnetic field as it flew over the planet. They were much more thorough than previous studies, to the point of reviewing measurements every 1.92 seconds.

Everything seemed ordinary, but the magnetometer marked a kind of zigzag at one point during its travels. The signal corresponded to a huge bubble of electrified gas: a cylindrical plasmoid at least 204,000 kilometers long and up to 400,000 kilometers wide.

Plasmoids are recognized as an important way for planets to lose mass. They detach from the part of the magnetic field of a planet that is expelled by the Sun. This phenomenon had been observed on Earth and other planets, but never on Uranus.

Over time, the plasma in plasmoids that escapes into space drains ions from the planet’s atmosphere, significantly altering their composition. In the case of Mars, the process ended up transforming it radically: it went from being a humid planet with a thick atmosphere to the dry world that we see today.

It’s not clear yet how Uranus’ atmospheric escape has affected the planet thus far, as scientists only got a tiny glimpse at this process. But the new discovery can help get some answers. “It’s why I love planetary science,” DiBraccio said. “You’re always going somewhere you don’t really know.”

The study was published in Geophysical Research Letters

Focusing on Arrokoth promises to reveal the Kuiper Belt’s secrets

Out beyond the orbit of Neptune and the solar system’s seven other major planets lies a ring of icy bodies known as the Kuiper Belt. The disc that is 20 times as wide and an estimated 200 times as dense as the asteroid belt houses a wide array of objects, including its most famous inhabitant — the dwarf planet Pluto. But, it holds more than objects of ice and rock. The Kuiper Belt may hold the secrets of how the planets of the solar system formed, and the raw materials that created the worlds around us and our own planet. 

“The Kuiper Belt is a repository of the solar system’s most primordial material and the long-sought nursery from which most short-period comets originate,” explains David C. Jewitt, an astronomer based at the University of California, Los Angeles, who is renowned for his study of the solar system and its smaller bodies. “The scientific impact of the Kuiper Belt has been huge, in many ways reshaping our ideas about the formation and evolution of the Solar System.”

Researchers now stand on the verge of unlocking these secrets with the investigation of the Kuiper Belt contact binary Arrokoth (previously known as ‘Ultima Thule’). On January 2019, the object — named for the Native American word for ‘sky’ — became the most distant object ever visited by a man-made spacecraft.

“Most of what we know about the belt was determined using ground-based telescopes. As a result, Kuiper Belt studies have been limited to objects larger than about 100 km because the smaller ones are too faint to easily detect,” says Jewitt. “Now, 5 years after its flyby of the 2000-km-diameter Kuiper Belt object Pluto, NASA’s New Horizons spacecraft has provided the first close-up look at a small, cold classical Kuiper Belt object.”

The data collected by the New Horizons probe has allowed three separate teams of researchers to conduct the most in-depth investigation of a Kuiper Belt object ever undertaken. In the process, they discovered that our current knowledge of how these objects form is very likely incorrect. From all the evidence the three teams collected, it seems as Kuiper Belts form as a result of a far more delicate, low-velocity process than previously believed. As most astrophysicists believe that these objects — planetesimals — acted as the seeds from which the planets grew, this new model changes our idea of how the solar system formed.

How Kuiper Belt Bodies Get in shape

The majority of the clues as to Arrokoth’s low-velocity formation originate from its unusual binary lobed shape. The larger lobe is joined to the smaller lobe by an extremely narrow ‘neck.’ What is especially interesting about this shape — reminiscent of a bowling pin or a snowman — is that the lobes are perfectly aligned. 

Scientists have used all available New Horizons images of Arrokoth, taken from many angles, to determine its 3D shape, as shown in this animation. The shape provides additional insight into Arrokoth’s origins. The flattened shapes of each of Arrokoth’s lobes, as well as the remarkably close alignment of their poles and equators, point to an orderly, gentle merger of two objects formed from the same collapsing cloud of particles. Arrokoth has the physical features of a body that came together slowly, with ‘locally-sourced’ materials from a small part of the solar nebula. An object like Arrokoth wouldn’t have formed, or look the way it does, in a more chaotic accretion environment. (NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Roman Tkachenko)

John Spencer, Institute Scientist in the Department of Space Studies, Southwest Research Institute in Boulder, Colorado, led a team of researchers that reconstructed Arrokoth’s 3-dimensional shape from a series of high resolution black and white images. Spencer’s paper concludes that Arrokoth’s lobes are much flatter than was previously believed but despite this, both lobes are denser than expected.

William McKinnon, Professor of Earth and Planetary Sciences at the Califonia Institute of Technology, and his team ran simulations of different formation methods to see which conditions led to the shape recreated and Spencer and his colleagues.

Velocity simulations of the formation of Arrokoth show that the unique shape of the bi-lobed comtact binary could only be acheived by a low-velocity gathering of small particles. (W.B McKinnon, et al)
Velocity simulations of the formation of Arrokoth show that the unique shape of the bi-lobed contact binary could only be achieved by a low-velocity gathering of small particles. (W.B McKinnon, et al)

McKinnon and his team discovered that the shape of Arrokoth could only be achieved as a result of a low-velocity formation–around 3 m/s. This presents a problem to current theories of how planetesimals form.

The suggested method of planetesimal formation suggests high-velocity particles smashing together in a process called hierarchical accretion. The simulations that McKinnon produced suggest that such high-velocity collisions would not have created a larger body, but rather, would have blown it apart. The geometrical alignment of the larger and smaller lobes indicates to the team that they were once co-orbiting bodies which gradually lost angular momentum and spiralled together, resulting in a merger.

“Arrokoth’s delicate structure is difficult to reconcile with alternative models in which Arrokoth Kuiper Belt objects are fragments of larger objects shattered by energetic collisions,” Jewitt says. This supports a method of planetesimal formation called ‘cloud collapse.’

Jewitt, Science, (2020)

“A variety of evidence from Arrokoth points to gravitational collapse as the formation mechanism.  The evidence from the shape is probably most compelling,” William Grundy of Lowell Observatory says. “Gravitational collapse is a rapid but gentle process, that only draws material from a small region. Not the much more time consuming and violent process of hierarchical accretion – merging dust grains to make bigger ones, and so on up through pebbles, cobbles, boulders, incrementally larger and larger,
with more and more violent collisions as the things crashing into each other.”

Grundy, whose team analysed the thermal emissions from Arrokoth’s ‘winter’ side, goes on to explain that the speed at which cloud collapse occurs and the fact that all the material that feeds it is local to it means that all the Kuiper planetesimals should be fairly uniform.

Cold Classicals: Untouched and unpolluted

Arrokoth is part of a Kuiper Belt population referred to as ‘cold classicals,’ this particular family of bodies is important to astrophysicists researching the origins of the solar systems. This is because, at their distance from the Sun within the Kuiper Belt, they have remained virtually untouched by both other objects and by the violent radiation of the Sun.

As many of these objects, Arrokoth in particular, date back 4 billion years to the very origin of the solar system, they hold an uncontaminated record of the materials from which the solar system emerged and of the processes at play in its birth.

Arrokoth's relative smoothness can be seen from comparisons to comets found in other areas of the solar system (J. R. Spencer et al., Science10.1126/science.aay3999 (2020).
Arrokoth’s relative smoothness can be seen from comparisons to comets found in other areas of the solar system (J. R. Spencer et al., Science10.1126/science.aay3999 (2020).

Arrokoth has a relatively smooth surface in comparison with other comets, moons and planets within the solar system. It does show the signs of a few impacts, with one very noticeable 7km wide impact crater located of the smaller lobe. This few craters dotted across Arrokoth’s surface do seem to point to a few small high-velocity impacts. The characteristics of Arrokoth’s cratering allowed the team in infer its age of around 4 billion years. This places its birth right around the time the planets had begun to form in the solar system.

“The smooth, relatively un-cratered surface shows that Arrokoth is relatively pristine, so evidence of its formation hasn’t been destroyed by subsequent collisions,” Spencer explains. “The number of craters nevertheless indicates that the surface is very old, likely dating back to the time of accretion.

“The almost perfect alignment of the two lobes, and the lack of obvious damage where they meet, indicate gentle coalescence of two objects that formed in orbit around each other, something most easily accomplished by local cloud collapse.”

Heatseekers

As mentioned above, Will Grundy and his team were tasked with the analysis of thermal emissions in the radio band emitted by the side of Arrokoth facing away from the Sun.

W. M. Grundy et al., Science
10.1126/science.aay3705 (2020).

“We looked at the thermal emission at radio wavelengths from
Arrokoth’s winter night side.  Arrokoth is very cold, but it does still emit thermal radiation,” Grundy says. “The signal we saw was brighter, corresponding to a warmer temperature than expected for the winter surface temperature.  Our hypothesis is that we are seeing emission from below the surface, at depths where the warmth from last summer still lingers.”

Grundy’s team also looked at the colour imaging of Arrokoth with the aim of determining what it is composed of. “We looked at the variation of colour across the surface, finding it to be quite subtle,” he says. “There are variations in overall brightness, but the colour doesn’t change much from place to place, leading us to suspect that the brightness variations are more about regional differences in surface texture than compositional differences.”

The team determined that Arrokoth’s dark red colouration is likely to be a result of the presence of ‘messy’ molecular jumbles of organic materials that occur when radiation drives the construction of increasingly complex molecules–known as tholins.

“One open question is where Arrokoth’s tholins came from,” Grundy says. “Were they already present in the molecular cloud from which the Solar System formed?  Did they form in the protoplanetary nebula before Arrokoth accreted? Or did they form after Arrokoth accreted, through radiation from the Sun itself?”

The researcher says that all three are possible, but he considers the uniformity of Arrokoth’s colouration to favour the first two possibilities over the third. The team also searched Arrokoth for more recognisable organic molecules, spotting methanol–albeit frozen solid–but, not finding any trace of water. Something which came as a surprise to Grundy. “It was surprising not to see a clear signature of water ice since that’s such a common material in the outer solar system. Typically, comets have
around 1% methanol, relative to their water ice.”

The team believe that this disparity arises from the fact that Arrokoth accreted in a very distinct chemical environment at the extreme edge of the nebula which collapsed to create the solar system.

“If it was cold enough there for carbon monoxide (CO) and methane (CH4) to freeze as ice onto dust grains, that would enable chemical mechanisms that create methanol and potentially destroy water, too. But those mechanisms could only work where these gases are frozen solid,” Grundy says.  “Arrokoth appears to be sampling a region of the nebula where such conditions held. 

“We have not seen comets so rich in methanol, which probably means we have not seen comets that formed in this outermost part of the nebula.  Most of them probably originally formed closer to the Sun (or else at a different time in nebular history when the chemical conditions were somewhat different).”

Looking to future Kuiper Belt investigations

Investigating Kuiper Belt objects is no walk in the park, with difficulties arising from both the disc’s distance from the Sun and from the fact that Kuiper Belt objects tend to be very small. Grundy explains that as sunlight falls off by the square of its distance, object s as far away as the Kuiper Belt require the most powerful telescopes to do much of anything.

“Sending a spacecraft for a close-up look is great to do, but it took New Horizons 13 years to reach Arrokoth,” Grundy says. “It’ll probably be some time yet before another such object gets visited up-close by a spacecraft.”

Investigations of the Kuiper Belt aren't easy, the next flyby might be decades away ( Kuiper Belt Illustration – laurinemoreau.com)
Investigations of the Kuiper Belt aren’t easy, the next flyby might be decades away ( Kuiper Belt Illustration – laurinemoreau.com)

“For flybys, the journey times are very long–we flew for 13 years to get there–navigation is difficult because we don’t know the orbits of objects out there very well, we’d only been tracking Arrokoth for 4 years,” Spencer explains. “The round-trip light time is long, which makes controlling the spacecraft more challenging, and light levels are very low, so taking well-exposed, unblurred, images is difficult.”

Spencer adds that from Earth, objects like Arrokoth are mostly very faint, meaning only a small fraction of them have been discovered and learning about their detailed properties is difficult even with large telescopes. These difficulties mean that one of the things left to discover is just how common bi-lobed contact binaries like Arrokoth are in the Kuiper Belt. “Some evidence from lightcurves suggests up to 25% of cold classical could be contact binaries,” he says. ” We know that many of them are binaries composed of two objects orbiting each other, however.”

Fortunately, telescope technology promises to make leaps and bounds over the coming decades, with the launch of the space-based James Webb Space Telescope (JWST) in 2021 and the completion of the Atacama Desert based Extremely Large Telescope (ELT) in 2026.

“Both will help,” says Grundy.  “Larger telescopes are needed to collect more light and feed it to more sensitive instruments.  JWST and the new generation of extremely large telescopes set to come online over the coming years will enable new investigations of these objects.”

In terms of future spacecraft visits, Grundy believes that researchers and engineers should be thinking small, literally: “If technical advances were to enable highly miniaturized spacecraft to be flown to the Kuiper belt more quickly, that could enable a lot of things.  The big obstacles to doing that with today’sCubeSats are power, longevity, and communications, but the rapid advance of technology makes me hopeful that it will be possible to do a whole lot more with tiny little spacecraft within a few decades. 

“It’s funny how progress calls for ever bigger telescopes and ever smaller
spacecraft.”

 Future advances in telescope technology promised more detailed examinations of Kuiper Belt objects like Arrokoth. (NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/National Optical Astronomy Observatory)
Future advances in telescope technology promised more detailed examinations of Kuiper Belt objects like Arrokoth. (NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/National Optical Astronomy Observatory)

Of course one of the most lasting changes that result from this landmark triad of studies on Arrokoth published in Science is the move away from hierarchical formation models and the adoption of a gravitational or cloud collapse model to explain the creation of planetesimals. This shift will resolve one of the long-standing issues with the hierarchical model, the fact that they work quite well to grow things from dust size to pebble size, but once pebble size is reached, the particles quickly spiral-in toward the Sun. 

“I think it will shift the focus to the circumstances that trigger the collapse.  It’s a very fast way of making a planetesimal–decades instead of hundreds of millennia–but the circumstances have to be right for instabilities to concentrate solids enough for them to collapse,” Grundy explains. “It will be interesting to map out where and when planetesimals should form, what their size distributions should be, and where the solids that they are formed from should have originated.”


Original research:

W. M. Grundy et al., Science
10.1126/science.aay3705 (2020).

W. B. McKinnon et al.,
Science 10.1126/science.aay6620

J. R. Spencer et al., Science
10.1126/science.aay3999 (2020).

D. C. Jewitt et al., Science
10.1126/science.aba6889 (2020).

Arrokoth--or as it was previously known Ultima Thule--may reveal secrets about the formation of the solar system (NASA, JOHNS HOPKINS UNIVERSITY APPLIED PHYSICS LABORATORY, SOUTHWEST RESEARCH INSTITUTE, ROMAN TKACHENKO)

Arrokoth, the ‘Space Snowman’, sheds new light on how the solar system formed

Arrokoth--or as it was previously known Ultima Thule--may reveal secrets about the formation of the solar system (NASA, JOHNS HOPKINS UNIVERSITY APPLIED PHYSICS LABORATORY, SOUTHWEST RESEARCH INSTITUTE, ROMAN TKACHENKO)
Arrokoth–or as it was previously known Ultima Thule–may reveal secrets about the formation of the solar system (NASA, JOHNS HOPKINS UNIVERSITY APPLIED PHYSICS LABORATORY, SOUTHWEST RESEARCH INSTITUTE, ROMAN TKACHENKO)

Located beyond the orbit of Neptune and within the Kuiper Belt — a massive circumstellar disc of small remnants left over from the formation of the solar system — Arrokoth (previously known as ‘Ultima Thule’) represents the most distant and primitive object ever to visited by a man-made space probe. 

Revealed in a small amount of data collected during a January 2019 flyby conducted by the New Horizons probe, the double-lobed contact binary— or Kuiper Belt object 2014 MU69 to give it its formal name — is the subject of three new papers due to be published in the journal Science. The key findings of these studies were revealed at a press briefing held in Seattle, Washington, on 13th February 2020.

The research provides us with a stunningly detailed picture of the compact binary’s composition and origins and suggests a rethink of how planetary building blocks–planetesimals form.

“Data from Arrokoth has given us clues about the formation of planets and our cosmic origins,” says Marc Buie, of the Southwest Research Institute, who was part of the New Horizons team that first discovered the object. “We believe this ancient body, composed of two distinct lobes that merged into one entity, may harbour answers that contribute to our understanding of the origin of life on Earth.”

New Horizons Path of Exploration (NASA)

The authors believe that their results could help rule out a hierarchical formation model of planetesimal formation, in which objects from different areas of the nebula of gas and dust violently collide to create larger bodies.

The shape of Arrokoth, with its two distinctive lobes, seems to favour a much more delicate formation process, that of local cloud collapse. This would involve regions of the nebula collapsing with smaller particles gradually accumulating together.

If planetesimals form differently then previously modelled, the fact that they are the building blocks of the planets means that we may also have to revise our ideas of how the planets themselves form.

As the planetesimal is composed of pure and unchanged material, its detailed study could answer long-standing questions about the elements which were present during the solar system’s planet-formation phase.

“The mission of the New Horizon probe was to explore the solar system’s ‘third zone’,” Alan Stern, the principal investigator of the New Horizons mission says describing the Kuiper Belt where icy planetesimals and dwarf planets lurk. “It is the best-preserved region of the solar system, important for understanding its origins.”

Each of the three separate papers focuses on different aspects of Arrokoth’s formation and composition, offering new insights into planetesimals and the conditions and composition of the early solar system. 

Three papers, three lines of evidence pointing to a new paradigm of planetesimal formation

William McKinnon and his team investigated how Arrokoth got its unique binary shape discovering that its two ‘lobes’ were once separate independent bodies. 

McKinnon and his team believe that the two separate objects which comprise Arrokoth formed in the same vicinity joined together in a surprisingly gentle process. As hierarchical accretion, is anything but gentle McKinnon and his team think that Arrokoth formed as a result of a local collapse of the nebula. 

“They’re just touching, it’s almost as if they’re kissing,” McKinnon, Professor of Earth and Planetary Sciences at the California Institute of Technology about the two lobes of Arrokoth. “There’s no evidence that the merger of these two lobes was violent. There’s no sign of catastrophic disruption.

“The merger speed must have been very low.”

The two dominant methods of planetesimal formation. Observations of Arrokoth may have ruled out high-velocity model. (McKinnon)

Whilst McKinnon and his team focused on the formation of Arrokoth’s distinctive shape, researchers led by John Spencer were studying that shape in painstaking detail. 

Spencer and his colleagues reveal that Arrokoth’s binary lobes are flattened in shape with a greater volume than originally believed. They are also almost perfectly aligned. “This tells us these are not objects that just blundered together,” Spencer “They have orbited each other for a long time, gently drifting together.”

The team have also been able to ascertain details about the surface of the contact binary, describing in their paper a smooth face with only slight cratering. This means that Arrokoth stands out from previously visited bodies within the solar system, having been struck by very few other objects. The greater consequence is that Arrokoth’s composition is unpolluted and thus may represent our best chance of studying the building blocks of the solar system.

Other comets that form closer to the Sun evolve very quickly as a result of the intense environments they find themselves in. In comparison, planetesimals that form far away from the Sun remain relatively unchanged, in Arrokoth’s case, for 4 billion years.

Will Grundy and the research team he worked with were charged with investigating the composition, colour, and temperature of Arrokoth’s surface. They found that the planetesimal’s distinctive and uniform red hue is a result of the presence of unidentified complex organic molecules — molecules formed from carbon, nitrogen, oxygen amongst other elements–present with methanol ice.

Grundy’s paper puts forward several suggestions as to how this frozen methanol could have formed on the Kuiper Belt object, including formation by irradiation of mixed water and methane ice by cosmic rays. The team was unable to detect the presence of water on Arrokoth, but they believe it could yet be present, currently ‘masked’ or hidden from view. 

The uniformity of the compact binary’s surface colour and composition provide the third line of evidence in support of the theory that it formed as a result of local nebula collapse. 

Stern does not downplay the significance of this evidence supporting a new paradigm of planetesimal formation–local cloud collapse. Comparing it to the discovery of the Cosmic Background Radiation which finally settled competition between different models of the origin of the universe he says: “This is a wonderful scientific present. It is truly a watershed moment.”

Stern concludes that every one of the attributes of Arrokoth observed point towards the cloud collapse model. As for the future, he says that the New Horizons mission has inspired other researchers to revisit another occupant of the Kuiper Belt– the dwarf planet Pluto.

Stern also points out that even though the New Horizons probe has “plenty of gas left in the tank,” the ideal mission would study Pluto for a period of a few years before moving off and investigating other bodies in the Kuiper Belt.

“We’re pretty excited, but it’s going to take a lot of work.”

Astrophysicists find more evidence of ‘wandering’ black holes

Artist’s conception of a dwarf galaxy, its shape distorted, most likely by a past interaction with another galaxy, and a massive black hole in its outskirts (pullout). The black hole is drawing in material that forms a rotating accretion disc and generates jets of material propelled outward. Image credit: Sophia Dagnello, NRAO/AUI/NSF

Dwarf galaxies have traditionally been considered too small to host massive black holes, but new research emerging from Montanna State University (MSU) has revealed dozens of examples. The research, published in the Astrophysical Journal has delivered another surprise, these black holes aren’t located where scientists usually expect to find them.

“All of the black holes I had found before were in the centres of galaxies,” says Amy Reines, an assistant professor in the Department of Physics in the College of Letters and Science. “These were roaming around the outskirts. I was blown away when I saw this.”

Reines and her team searched 111 dwarf galaxies within a radius of a billion-light-years of Earth using the National Science Foundation’s Karl G. Jansky Very Large Array at the National Radio Astronomy Observatory, Albuquerque, New Mexico. During the course of their search, they identified 13 galaxies that very probably host black holes, the majority of which were not centralised. 

Reines is also a researcher in the MSU’s eXtreme Gravity Institute, which unites astronomers and physicists in order to study phenomena in which the gravitational influence is so powerful that it blurs the separation of space and time. This includes events and objects such as neutron stars, black holes, mergers and collisions between the two and even, the initial extreme period of rapid expansion of the universe — the big bang. 

The researcher explains that whilst stellar-mass black holes — those with a mass of up to 10 times that of our Sun — form as large stars undergo gravitational collapse, we are, thus far, uncertain how supermassive black holes form. This class of black hole which can have masses of up to billions of times that of the Sun is most commonly found in the centre of galaxies. 

This is certainly the case with our galaxy, the Milky Way, which hosts the supermassive black hole Sagittarius A* (SgrA*) at its centre. Dwarf galaxies are smaller than spiral galaxies like the Milky Way, containing a few billion stars rather than 100–400 billion as spiral galaxies tend to.

The results collected by Reines confirm computer simulations generated by Jillian Bellovary, assistant professor at Queensborough Community College, New York and Research Associate at the American Museum of Natural History. 

How black holes get lost

Bellovary’s computer simulations suggested that black holes could be disturbed from the centre of dwarf galaxies by interactions they undergo as they travel through space. This result coupled with Reines’ study have the potential to change the way we look for black holes in dwarf galaxies going forward. This change in thinking could also impact theories of how both dwarf galaxies and supermassive black holes form. 

“We need to expand searches to target the whole galaxy, not just the nuclei where we previously expected black holes to be,” Reines adds.

No stranger for the search for black holes, Reines has been hunting these events for a decade, ever since she was a graduate student at the University of Virginia. Whilst she initially focused on star formation in dwarf galaxies, her research led her to something else that captured her interest: a massive black hole “in a little dwarf galaxy where it wasn’t supposed to be.”

Henize 2–10: a dwarf galaxy that hides a massive secret ( Reines et al. (2011))
Henize 2–10: a dwarf galaxy that hides a massive secret ( Reines et al. (2011))

The little dwarf galaxy she refers to is Heinze 2–10, located 30-million-light-years from Earth, which had previously been believed too small to host a massive black hole. “Conventional wisdom told us that all massive galaxies with a spheroidal component have a massive black hole and little dwarf galaxies didn’t,” Reines explains, adding that when she discovered such a relationship it was a “eureka” moment. After publishing these findings in the journal Nature she continued searching for further black holes in dwarf galaxies. “Once I started looking for these things on purpose, I started finding a whole bunch,” Reines says.

Visible-light images of galaxies that VLA observations showed to have massive black holes. Center illustration is artist’s conception of the rotating disk of material falling into such a black hole, and the jets of material propelled outward. Image credit: Sophia Dagnello, NRAO/AUI/NSF; DECaLS survey; CTIO
Visible-light images of galaxies that VLA observations showed to have massive black holes. Center illustration is artist’s conception of the rotating disk of material falling into such a black hole, and the jets of material propelled outward. Image credit: Sophia Dagnello, NRAO/AUI/NSF; DECaLS survey; CTIO

Changing her tactics by shifting from visual data from radio signals, Reines uncovered over 100 possible black holes in her first search of a sample that included 40,000 dwarf galaxies. In current search, as described in the latest paper, Reines returned to radio searches, hunting for radio signatures with that sample. This, she says, should allow her to find massive black holes in star-forming dwarf galaxies, even though she has only found one thus far. 

“When new discoveries break our current understanding of the way things work, we find even more questions than we had before,” comments Yves Idzerda, head of the Department of Physics at MSU.

As for Reines, the search continues. 

“There are lots of opportunities to make new discoveries because studying black holes in dwarf galaxies is a new field,” she said. “People are definitely captivated by black holes. They’re mysterious and fascinating objects.”

Original research: https://iopscience.iop.org/article/10.3847/1538-4357/ab4999

Oldest material on Earth is stardust found in meteorite

The oldest material known to exist on Earth was just discovered by a group of researchers, working on a meteorite that fell fifty years ago in Australia. The space object, which felt on Earth in the 1960s, had dust grains within that were formed 5 to 7 billion years ago, preceding the formation of the solar system.

Some of the pre-solar grains in the Murchison meteorite (inset) could have come from evolved stars similar to the Egg Nebula (pictured). Credit ESA/Hubble/NASA

Stars have life cycles, born when dust and gas floating through space find each other and then collapse in on each other and heat up. They continue to burn for billions of years until they die, setting off a supernova explosion. When that happens, they create particles known as stardust that are expelled into the universe eventually forming new stars.

Researchers from the Field Museum, the University of Chicago, ETH Zurich and other universities found presolar grains in the meteorite, which are minerals formed before the Sun was born. The stardust was trapped in the meteorites and remained unchanged for billions of years.

Presolar grains are usually hard to find as they are only found in about 5% of the meteorites that have fallen to Earth. The Murchinson meteorite, which fell in Australia in 1969, was filled with them. The study, published in the journal Proceedings of the National Academy of Sciences, now took a closer look at them.

“It starts with crushing fragments of the meteorite down into a powder,” said co-author Jennika Greer, from the Field Museum and the University of Chicago. “Once all the pieces are segregated, it’s a kind of paste, and it has a pungent characteristic – it smells like rotten peanut butter.”

The researchers worked to determine the age of the grains by measuring how long they had been exposed to cosmic rays in space. The rays are high-energy particles that travel through the galaxy and penetrate solid matter.

Some of the grains in the sample were the oldest ever discovered, the study found. Most of them were 4.6 to 4.9 billion years old, and some were even older than 5.5 billion years, something never seen before. For context, the Sun is 4.6 billion years old, and Earth is 4.5 billion.

Lead author Philipp Heck said: “Only 10% of the grains are older than 5.5 billion years, 60% of the grains are “young” (at) 4.6 to 4.9 billion years old, and the rest are in between the oldest and youngest ones. I am sure there are older pre-solar minerals in Murchison and other meteorites, we just haven’t found them yet.”

The findings revive the debate over whether or not new stars are formed at a steady rate or whether there are highs and lows in the number of new starts over time. Also, thanks to the findings, researchers now know that pre-solar grains float through space together in large clusters.

Mineral never before seen in nature is discovered in a meteorite from 1951

Working on a meteorite first discovered in 1951, a group of researchers has now found a rare form of an iron-carbide mineral never before seen in nature. The finding is the key prerequisite for the new mineral to later be officially recognized as such by the International Mineralogical Association (IMA).

Wedderburn Meteorite. Source: Victoria Museum

The Wedderburn meteorite was found in a small town with the same name in Australia. Researchers have been working on it for decades to figure out the secrets behind it. Now, a group lead by mineralogist Chi Ma has decoded another one with the new mineral.

Only a third of the original meteorite remains intact at the Museum Victoria in Australia. The rest was divided into a series of slices and used to analyze the content of the meteorite. The analysis showed traces of gold and iron, as well as other rare minerals such as kamacite, taenite and troilite.

Now we can add a new mineral to that list, known as ‘edscottite’ in honor of meteorite expert and cosmochemist Edward Scott from the University of Hawaii. It’s a significant discovery as never before researchers had been able to confirm that this atomic formulation of iron carbide mineral occurs naturally. Previously, only the synthetic form of the iron carbide mineral was known.

“We have discovered 500,000 to 600,000 minerals in the lab, but fewer than 6,000 that nature’s done itself,” Museums Victoria senior curator of geosciences Stuart Mills, who wasn’t involved with the new study, told The Age.

There’s not much clarity yet on how the natural edscottite ended up outside of Wedderburn in Australia. But the first theories are already available. Planetary scientists Geoffrey Bonning, a researcher at Australian National University, believes the mineral could have formed in the core of an ancient planet.

A long time ago, this planet could have produced a big cosmic collision that involved another planet or moon or asteroid. The blast would have led to fragmented parts of the world travel across time and space, according to Boning. This would explain the finding of the fragment in Wedderburn.

The findings were published in American Mineralogist, part of the Journal of Earth and Planetary Materials.

The rocket carrying CHEOPS splits depositing its cargo into a low-Earth orbit. (ESA)

New European exoplanet-hunting telescope launches into space

After an initial setback yesterday (17/12/19) due to a software error, the European Space Agency’s (ESA) CHaracterising ExOPlanets Satellite — or CHEOPS — telescope has finally launched from the European Spaceport in Kourou, French Guiana.

Blast off: CHEOPS begins its journey to space (NASA)

CHEOPS was aboard a Russian Soyuz-Fregat rocket which blasted off at 9:54 am European time. The Rocket will take approximately 145 minutes to place the CHEOPS unit into a rare pole to pole low-Earth orbit. 

The telescope hitched a ride with an Italian radar satellite, the rocket’s primary payload. 

CHEOPS being loaded aboard its method of transport (ESA)

CHEOPS is the result of a collaboration between 11 member countries within the ESA, with Switzerland taking the lead on the project. Two of the country’s leading Universities — the University of Geneva and the University Bern — worked together to equip CHEOPS with a state of the art photometer.

This powerful device will measure changes in the light emitted by nearby stars as planets pass by — or transit — them. This examination reveals many details about a planet’s characteristics, its diameter, and details of its atmosphere in particular. 

Another type of lift-off (ESA)

By combining a precise measurement of diameter with a measurement of mass, collected by an alternative method, researchers will then be able to determine a planet’s density. This, in turn, can lead to them deducing its composition and internal structure. 

CHEOPS was completed in a short time with an extremely limited budget of around 50-million Euros.

“CHEOPS is the first S-class mission for ESA, meaning it has a small budget and a short timeline to completion,” explains Kate Issak, an ESA/CHEOPS project researcher. “Because of this, it is necessary for CHEOPS to build on existing technology.”

CHEOPS: Informed by the past, informing the future

The project is acting as a kind of ‘middle-man’ between existing exoplanet knowledge and future investigations. It is directed to perform follow-up investigations on 400–500 ‘targets’ found by NASA planet-hunter Transiting Exoplanet Survey Satellite (Tess) and its predecessor, the Kepler observatory. Said targets will occupy a size-range of approximately Earth-Neptune.

Reaching new heights (ESA)

This mission then fits in with the launch of the James Webb Telescope in 2021 and further investigation methods such as the Extremely Large Telescope array in the Chilean desert, set to begin operations in 2026. It will do this by narrowing down its initial targets to a smaller set of ‘golden targets’. Thus, meaning its investigation should help researchers pinpoint exactly what planets in close proximity to Earth are worthy of follow-up investigation. 

“It’s very classic in astronomy that you use a small telescope ‘to identify’, and then a bigger telescope ‘to understand’ — and that’s exactly the kind of process we plan to do,” explains Didier Queloz, who acted as chair of the Cheops science team. “Cheops will now pre-select the very best of the best candidates to apply to extraordinary equipment like very big telescopes on the ground and JWST. This is the chain we will operate.”

Queloz certainly has pedigree when it comes to exoplanets. The astrophysics professor was jointly awarded the 2019 Nobel Prize in Physics for the discovery of the first exoplanet orbiting a Sun-like star with Michel Mayor. 

The first task of the science team operating the satellite, based out of the University of Bern, will be to open the protective doors over the 30 cm aperture telescope — thus, allowing CHEOPS to take its first glimpse of the universe.