Category Archives: Astronomy

The moon has a new crater — this time, created by a rogue rocket

A piece of space junk just impacted right into the far side of the moon, creating a shiny new crater as wide as 20 meters (65 feet). The debris, a discarded part of a rocket the size of a school bus, had been floating in space for over seven years – finally ending its long-term trajectory by heading right into the lunar surface at 5,800 miles per hour.

But the controversy around the object is far from over.

Image credit: Pixabay.

We still don’t know a lot of details about the impact. The crash took place on the far side of the moon, meaning it was out of the reach of ground-based telescopes. NASA’s Lunar Reconnaissance Orbiter wasn’t likely in a position to observe the crash, but the agency has already said it will seek out the resulting crater — but the process will take weeks or even months.

“NASA’s Lunar Reconnaissance Orbiter will use its cameras to attempt to identify the impact site and determine any potential changes to the lunar environment resulting from this object’s impact,” an agency spokesman told The Wall Street Journal. “The search for the impact crater will be challenging and might take weeks to months.”

It’s the first known unintentional lunar collision involving a piece of space hardware, not considering the probes that crashed while attempting to land on the moon. The crater is estimated to be located near the naturally-formed Hertzsprung Crater, which is 570 kilometers (354 miles) wide. This will be confirmed by NASA with further work.

The origin of the rocket

Astronomers have long debated the exact identity of the rocket. It’s an upper state booster discarded from a high-altitude satellite launch – either a SpaceX rocket launched in 2015 or a Chinese rocket launched in 2014. However, both have denied ownership. It’s roughly 12 meters long (40 feet) and weighs about 4,500 kilograms.

The first one to predict the impact on the moon was astronomer Bill Gray, who is in charge of the Project Pluto program that monitors faraway space objects. Gray initially calculated that the impactor was the upper stage of a SpaceX rocket launched in 2015, but then corrected his prediction and suggested it was likely the Chinese rocket.

So it’s a complicated story, one that will probably continue to be debated, at least until we get a more detailed view of the crash site. The Lunar Reconnaissance Orbiter has captured the lunar surface in much detail, including things left behind by astronauts. Experts will have to go through before-and-after photos of the specific spot where the rocket impacted to better identify the crater.

The shape of the crater and the dust that came out of it should show how the rocket was oriented at the time of impact, Paul Hayne, an astrophysics professor at the University of Colorado Boulder wrote in The Conversation. A vertical orientation would produce a circular feature, while an asymmetric debris pattern might indicate a belly flop.

If observations are done fast, the lunar orbiter’s infrared instrument could detect glowing-hot material inside the crater, Hayne explained. This could be used to estimate the amount of heat generated from the impact. If using the orbiter fast enough isn’t an option, NASA could also use high-resolution images to estimate the amount of melted material in the crater.

In addition to helping settle the debate on where the object came from, studying the impact site could be useful for another reason. Crater formation is a persistent phenomenon in the Solar System but the physics of the process is not well understood yet. That’s why observing the rocket impact and the resulting crater might be very valuable for scientists to produce better impact simulations – also improving our knowledge of the lunar surface properties.

The James Webb telescope could detect aliens by looking for signs of pollution

The James Webb Space Telescope isn’t even fully operational yet, but researchers are getting more and more excited about what it can do. In a recent study, researchers claim we may be on the cusp of being able to discover other civilizations based on specific types of pollution in their planets’ atmosphere.

A total ozone map of the Earth. Image credits: NASA.

The alien ozone hole

Human society has changed a lot over the centuries, but the shifts in the past 200 years have been truly mind-bending. The Industrial Revolution changed how many things work, fueling, well, a revolution in our society. If you were a patient alien scouting the Earth from close by (or from farther away, but with a good enough telescope) you may have seen the signs of this industrial revolution happening through the emissions we produced by burning fossil fuels.

But they could see other forms of pollution even better.

Chlorofluorocarbons (CFCs) are a type of chemical notorious for causing the ozone hole in the 1980s (until regulations entered into force to address the problem). They’re produced industrially as refrigerants and cleaning agents — and if an alien civilization would resemble ours, it would likely also start producing them at some point. CFCs are also very unlikely to appear naturally so if you see them in a planet’s atmosphere, someone is producing them artificially. Furthermore, even if a civilization stops producing them or reduces their production (like we did), they still have a long life in the atmosphere, meaning they could be detected long after they’ve been produced.

This brings us to an interesting point: our most clear sign of civilization may also be one of our worst impacts on the planet — pollution. We don’t really know whether this would also be the case for an alien civilization but there’s a decent chance it is. Now, we could also have a way to detect this, thanks to the James Webb Space Telescope (JWST).

Looking for pollution on alien planets isn’t the main objective of the JWST, and its capability in this regard is limited. For instance, if a planet is too bright, it could drown out the CFC signal. So the new study focused on M-class stars — a type of dim, long-lived red dwarf. Researchers believe M-class stars make out the majority of stars in the universe.

A team of researchers led by Jacob Haqq-Misra, an astrobiologist at the Blue Marble Space Institute of Science, analyzed the JWST’s ability to detect CFC around a TRAPPIST-1, a typical red dwarf relatively close to Earth (40 light-years away). TRAPPIST-1 also has several Earth-sized planets within the habitable zone, so it would be a good place to start looking for alien civilizations (although M-stars, in general, aren’t considered to be conducive to life).

According to the study, there’s a good chance that the JWST could be able to detect CFC in this type of scenario.

“With the launch of JWST, humanity may be very close to an important milestone in SETI [the Search for Extra-Terrestrial Intelligence]: one where we are capable of detecting from nearby stars not just powerful, deliberate, transient, and highly directional transmissions like our own (such as the Arecibo Message), but consistent, passive technosignatures of the same strength as our own,” the researchers write in the study.

Funny enough, this detection isn’t necessarily reciprocal: just because we can detect potential CFCs around a planet doesn’t necessarily mean aliens could do the same for us. Remember when we said in order for the method to work, the planet needs to not be too bright? Well, the Sun is pretty bright, and it sends out enough light that it would obstruct much of the useful signal. So if an alien civilization were to exist closeby, there’s a chance we could be able to spot them without them being able to do the same thing to us. Of course, this is all speculation at this point, but it’s something that astronomers are looking into as JWST will soon become operational.

The telescope is currently in its calibration stage. James Webb is expected to offer researchers an unprecedented view of the universe, focusing on four main objectives:

  • light coming from the very first stars and galaxies that formed after the Big Bang;
  • galaxy formation and evolution;
  • star formation and planet formation;
  • planetary systems and the origins of life.

The study was published in arXiv and has not been peer-reviewed yet.

Annie Jump Cannon: the legend behind stellar classification

It is striking that today, we can not only discover but even classify stars that are light-years from Earth — sometimes, even billions of light-years away. Stellar classification often uses the famous Hertzsprung–Russell diagram, which summarises the basics of stellar evolution. The luminosity and the temperature of stars can teach us a lot about their life journey, as they burn their fuel and change chemical composition.

We know that some stars are made up mostly of ionised helium or neutral helium, some are hotter than others, and we fit the Sun as a not so impressive star compared to the giants. Part of that development came from Annie Jump Cannon’s contribution during her long career as an astronomer. 

The Hertzsprung diagram where the evolution of sun-like stars is traced. Credits: ESO.

On the shoulders of giantesses

Cannon was born in 1863 in Dover, Delaware, US. When she was 17 years old, thanks to her father’s support, she managed to travel 369 miles all the way from her hometown to attend classes at Wellesley College. It’s no big deal for teens today, but back then, this was an imaginable adventure for a young lady. The institution offered education exclusively for women, an ideal environment to spark in Cannon an ambition to become a scientist. In 1884, she graduated and later in 1896 started her career at the Harvard Observatory.

In Wellesley, she had Sarah Whiting as her astronomy professor, who sparked Cannon’s interest in spectroscopy:

“… of all branches of physics and astronomy, she was most keen on the spectroscopic development. Even at her Observatory receptions, she always had the spectra of various elements on exhibition. So great was her interest in the subject that she infused into the mind of her pupil who is writing these lines, a desire to continue the investigation of spectra.”

Whiting’s obituary in 1927, Annie Cannon.

Cannon had an explorer spirit and travelled across Europe, publishing a photography book in 1893 called “In the footsteps of Columbus”. It is believed that during her years at Wellesley, after the trip, she got infected with scarlet fever. The disease infected her ears and she suffered severe hearing loss, but that didn’t put an end to her social or scientific activities. Annie Jump Cannon was known for not missing meetings and participating in all American Astronomical Society meetings during her career.


At Radcliffe College, she began working more with spectroscopy. Her first work with southern stars spectra was later published in 1901 in the Annals of the Harvard College Observatory. The director of the observatory, Edward C. Pickering chose Cannon as the responsible for observing stars which would later become the Henry Draper Catalogue, named after the first person to measure the spectra of a star. 

Annie Jump Cannon at her desk at the Harvard College Observatory. Image via Wiki Commons.

The job didn’t pay much. In fact, Harvard employed a number of women as “women computers” that processed astronomic data. The women computer at Harvard earned less than secretaries, and this enabled researchers to hire more women computers, as men would have need to be paid more.

Her salary was only 25 cents an hour, a small income for a difficult job to look at the tiny details from the spectrographs, often only possible with magnifying glasses. She was known for being focused (possibly also influenced by her deafness), but she was also known for doing the job fast. Simply put,

During her career, she managed to classify the spectra of 225,000 stars. At the time, Williamina Fleming, a Scottish astronomer, was the Harvard lady in charge of the women computers. She had previously observed 10,000 stars from Draper Catalogue and classified them from letters A to N. But Annie Jump Cannon saw the link between the stars’ temperature and rearranged Fleming’s classification to the OBAFGKM system. The OBAFGKM system divides the stars from the hottest to the coldest, and astronomers created a popular mnemonic for it: “Oh Be A Fine Guy/Girl Kiss Me”.


“A bibliography of Miss Cannon’s scientific work would be exceedingly long, but it would be far easier to compile one than to presume to say how great has been the influence of her researches in astronomy. For there is scarcely a living astronomer who can remember the time when Miss Cannon was not an authoritative figure. It is nearly impossible for us to imagine the astronomical world without her. Of late years she has been not only a vital, living person; she has been an institution. Already in our school days she was a legend. The scientific world has lost something besides a great scientist.”

Cecilia Payne-Gaposchkin in Annie Jump Cannon’s obituary.
Annie Jump Cannon at Harvard University. Smithsonian Institution @ Flickr Commons.

Annie Jump Cannon was awarded many prizes, she became honorary doctorate of Oxford University, the first woman to receive the Henry Draper Medal in 1931, and the first woman to become an officer of the American Astronomical Society. 

Her work in stellar classification was followed by Cecilia Payne-Gaposchkin, another dame of stellar spectroscopy. Payne improved the system with quantum mechanics and described what stars are made of

Very few scientists have such a competent and exemplary career as Cannon. Payne continued the work left from Cannon, her advisor, Henry Norris Russell, then improved it with minimum citation. From that, we got today’s basic understanding of stellar classification. Her beautiful legacy has been rescued recently by other female astronomers who know the importance of her life’s work.

Scientists find a potentially habitable planet orbiting a dying star

A group of astronomers have identified a ring of planetary debris orbiting close to a dying star, some 117 light-years away from Earth, hinting at what could be a planet in a habitable zone where life could exist. If confirmed, it would be the first time a life-supporting world is discovered orbiting such a start, known as a “white dwarf.”

An artist’s impression of the white dwarf star WD1054–226 orbited by clouds of planetary debris and a major planet in the habitable zone. Image credit: The researchers.

While most large stars go supernova at the end of their evolution, medium and small ones with a mass of less than eight times than the one of the Sun usually become white dwarfs. They have a similar carbon and oxygen mass despite their small size. About 97% of the stars in the Milky Way will become white dwarfs, according to a previous study.

A team of researchers measured light from a white dwarf in the Milky Way called WD1054–226 using data from ground and space-based telescopes. They noticed something appeared to be passing regularly in front of the star, causing dips in the light. The pattern repeated every 25 hours, with the biggest dip every 23 minutes.

This indicates that the star is surrounded by a ring of 65 comet-sized or moon-sized orbiting objects, evenly spaced in their orbits by the gravitational pull of a nearby planet the size of Mars or Mercury. The objects are 2.6 million kilometers from the star, putting their temperature at 50ºC – in the middle of the range for liquid water.

“An exciting possibility is that these bodies are kept in such an evenly-spaced orbital pattern because of the gravitational influence of a nearby planet. Without this influence, friction and collisions would cause the structures to disperse, losing the precise regularity that is observed,” lead author Jay Farihi said in a statement.

Tracking white dwarfs

Finding planets orbiting white dwarfs is a massive challenge for astronomers because these stars are much fainter than the main-sequence stars, such as the Sun. So far, astronomers have only last year found tentative evidence of a gas giant, like Jupiter, orbiting a white dwarf. It’s estimated to be one or two times as massive as Jupiter.

For this new study, the researchers focused on WD1054–226, a white dwarf 117 light-years away from Earth. They recorded changes in its light over 18 nights, using a high-speed camera at the observatory La Silla in Chile. They also looked at data from NASA’s Transiting Exoplanet Survey Satellite (TESS) to better interpret changes in the light.

The habitable zone where the potential planet could be located is usually referred as the Goldilocks zone, taken from the children’s fairy tale. Since the concept was introduced in the 1950s, many stars have been shown to have a Goldilocks area. The temperature from the starts have to be just right so liquid water can exist on the surface.

Compared to big stars like the Sun, the habitable zone of white dwarfs is smaller and closer to the star, as white dwarfs emit less heat. The researchers estimated that the structures observed in the orbit were enveloped by the star when it was a red giant, so they are more likely to have formed or arrived recently than having survived the birth of the start.

“The possibility of a planet in the habitable zone is exciting and also unexpected; we were not looking for this.  However, it is important to keep in mind that more evidence is necessary to confirm the presence of a planet. We cannot observe the planet directly so confirmation may come by comparing computer models with further observations of the star and orbiting debris,” Farihi said.

The study was published in the journal of the Royal Astronomical Society.

The journey of galaxy clusters in billions of years

A new study modeled the dynamics and evolution of some of the largest known structures in the universe.

Extragalactic neighborhood. Credit: Wikimedia Commons.

Let’s take a moment to look at our position in the universe.

We are now living on a solar system orbiting the center of the Milky Way galaxy — which itself lies in the Local Group of galaxies neighboring a Local Void, a vast cluster of space with fewer galaxies than expected. Wait, we’re not done yet. These structures are part of a larger region that encompasses thousands of galaxies in a supercluster called the Laniakea Supercluster, which is around 520 million light-years across. 

A group of researchers has now simulated the movement of galaxies in the Laniakea and other clusters of galaxies starting when the universe was in its infancy (just 1.6 million years old) until today. They used observations from the Two Micron All-Sky Survey (2MASS) and the Cosmicflows-3 as the starting point for their study. With these two tools, they looked at galaxies orbiting massive regions with velocities of up to 8,000 km/s — and made videos describing those orbits.

Because the universe is expanding and that influences the evolution of these superclusters, we first need to know how fast the universe is expanding, which has proven to be very difficult to calculate. So the team considered different plausible universal expansion scenarios to get the clusters’ motion. 

Besides Laniakea, the scientists report two other zones where galaxies appear to be flowing towards a gravitational field, the Perseus-Pisces (a 250 million light-years supercluster) and the Great Wall (a cluster of about 1.37 billion light-years). In the Laniakea region, galaxies flow towards the Great Attractor, a very dense part of the supercluster. The other superclusters have similar patterns, the Perseus-Pisces galaxies flow towards the spine of the cluster’s large filament.

The researchers even predicted the future of these galaxies. They estimated the path of the galaxies to something like 10 billion years into the future. It is clear in their videos, the expansion of the universe affecting the big picture. In smaller, denser regions, the attraction prevails, like the future of Milkomeda in the Local Group.

The study has been accepted for publication in Astrophysical Journal.

Hubble spots black hole “giving birth” to new star

Black holes are the most massive objects in the universe. Their gravitational pull is so strong that nothing can escape it — not even light. But according to a new NASA study, black holes may play a more complex role in galactic ‘ecosystems’. Specifically, a black hole was found to be contributing to the formation of a new star in its vicinity, offering tantalizing clues about how massive black holes develop in the first place.

A pullout of the central region of dwarf starburst galaxy Henize 2-10 traces an outflow, or bridge of hot gas 230 light-years long, connecting the galaxy’s massive black hole and a star-forming region. Hubble data on the velocity of the outflow from the black hole, as well as the age of the young stars, indicates a causal relationship between the two. Image credits: NASA, ESA, Zachary Schutte (XGI), Amy Reines (XGI); Image Processing: Alyssa Pagan (STScI).

A stellar nursery

Some ten years ago, Amy Reines, then a graduate student, discovered a black hole in a galaxy about 30 million light-years away from Earth, in the southern constellation Pyxis. She knew something was off right away, but it wasn’t until recently that new Hubble observations shed light on the situation.

“At only 30 million light-years away, Henize 2-10 is close enough that Hubble was able to capture both images and spectroscopic evidence of a black hole outflow very clearly. The additional surprise was that, rather than suppressing star formation, the outflow was triggering the birth of new stars,” said Zachary Schutte, Reines’ graduate student and lead author of the new study.

The galaxy, called Henize 2-10, is a so-called “starburst” galaxy — a galaxy where stars are being formed at a much higher rate than normal, around 1,000 times faster. The galaxy is also relatively small — a so-called dwarf galaxy — and has a black hole at its center, much like the Milky Way.

Researchers were already aware of an unusual cocoon of gas in the area, but Hubble managed to also image an outflow linked to the central black hole. Although the process is not fully understood, astronomers do believe that black holes (or at least some black holes) do have an outflow despite their massive gravity. In Henize 2-10, this outflow moves at about a million miles per hour, slamming into the gas cocoon — and as it turns out, newborn stars follow the path of the outflow.

Image credits: Schutte and Reines (2022).

In large galaxies, the opposite happens: material falling towards the black hole forms jets of plasma that don’t allow the formation of stars. But apparently, in the less-massive Henize 2-10, the outflow has just the right characteristics to precipitate new star formation. Previously, studies mostly focused on larger galaxies, where there is more observational evidence. Dwarf galaxies are still understudied, and it’s only thanks to Hubble that researchers were able to study this.

“Hubble’s amazing resolution clearly shows a corkscrew-like pattern in the velocities of the gas, which we can fit to the model of a precessing, or wobbling, outflow from a black hole. A supernova remnant would not have that pattern, and so it is effectively our smoking-gun proof that this is a black hole,” Reines said.

The role that black holes play in the universe is one of the biggest puzzles in astronomy, and the more data comes in, the more it’s starting to look like this is not a straightforward role, but rather a complex one. For instance, it was just recently demonstrated that researchers realized that most (if not all) galaxies have a black hole at their center. The more massive the galaxy, the more massive the central black hole — or possibly, the other way around, and the mass of the black hole is affecting the galaxy.

But we don’t really know how these central black holes (often called supermassive black holes) formed. Some researchers suspect they formed like “regular” black holes and somehow accumulated more and more mass; others believe they could only have formed in special conditions in the early stages of the universe; a further competing theory claims that the “seeds” of these black holes come from dense star clusters that collapse gravitationally. The black hole in Henize 2-10 could offer clues about these theories.

The black hole in the galaxy remained relatively small over cosmic time and did not accumulate a lot of material. This would suggest that it’s relatively unchanged since its formation, essentially offering a window into the early days of the universe.

“The era of the first black holes is not something that we have been able to see, so it really has become the big question: where did they come from? Dwarf galaxies may retain some memory of the black hole seeding scenario that has otherwise been lost to time and space,” Reines concludes.

What does the universe sound like? The eerie world of cosmic sonification

Light is more than just what we see. The light spectrum can provide information about astrophysical objects — and in different wavelengths, it can provide different types of information. We can observe the sky through X-rays, visible light, gamma rays — all of which are waves at different frequencies. For sounds, something similar happens: it exists in many frequencies. High pitched sounds have higher frequencies than low ones, which is why electric guitars sound higher than bass guitars, their frequencies are a lot higher.

So what would happen if you would turn light (or other types of astronomic data) into sounds? This is technically called sonification — the use of non-speech data to represent sounds. You basically take some type of data and translate it into pitch, volume, and other parameters that define sound.

It’s not as silly or unheard of as it sounds. Scientists convert things into sounds for a number of reasons. For instance, take the Geiger counter, an electronic instrument used to measure ionizing radiation. If the radiation is high enough, you hear an increase of repetitions in the click sound from the instrument. The same can be done with astronomical data, with many lines of code, scientists can translate astronomical data into sounds. So, without further ado, here are some of the coolest sounds in the universe.

The Pillars of Creation

In the sonification in the Eagle Nebula, you can hear a combination of both optical and X-ray bands. The pitches change according to the position of the light frequencies observed, the result reminds us of a sci-fi movie soundtrack. As we listen to the features from the left to the right, the dusty parts form the Pillars as a whir, it’s eerily apparent that we’re hearing something cosmic.

Sonification Credit: NASA/CXC/SAO/K.Arcand, SYSTEM Sounds (M. Russo, A. Santaguida)

The Sun

Using Solar and Heliospheric Observatory (SOHO)’s data, we can listen to our star’s plasma flowing and forming eruptions. The sound is pretty peaceful for a 5,778 K environment.

Credits: A. Kosovichev, Stanford Experimental Physics Lab


In one of Parker Solar Probe’s flybys, the spacecraft collect data from Venus’ upper atmosphere. The planet’s ionosphere emits radio waves naturally that were easily sonified.

Video credit: NASA’s Goddard Space Flight Center/Scientific Visualization Studio

Bullet Cluster

The Bullet Cluster is famous for being proof dark matter is out there. In its sonification, the dark matter part (in blue) is lower, while the matter part (in pink) has a higher pitch. This is one of the most melodic cosmic sounds you’ll ever hear, though it does have a distinctively eerie tune as well.

Sonification Credit: NASA/CXC/SAO/K.Arcand, SYSTEM Sounds (M. Russo, A. Santaguida).

A supernova

This sonification is different from the others. We hear the sounds emanating from the centre of the Tycho’s supernova remnant and continue with the sounds of the stars visible in that plane. Inside the remnant, the sound is continuous, outside we hear distinct notes which are the stars nearby. 

Sonification Credit: NASA/CXC/SAO/K.Arcand, SYSTEM Sounds (M. Russo, A. Santaguida)

Cosmic music

With a musical approach, the sci-art outreach project SYSTEM Sounds, not just sonify data, but also make sure the sounds are harmonic. It’s even better when nature provides naturally harmonical systems.

The most incredible sonification of all comes from the TRAPPIST-1 system, a relatively close system “just” 39.1 light-years away. Six of the planets orbiting the red dwarf are in an orbital resonance that means they pull each other in pairs and their rotation match in the integer ratios 8:5, 5:3, 3:2, 3:2, 4:3, and 3:2. So the first two planets influence each other gravitationally — for every eight orbits completed by TRAPPIST-1a, TRAPPIST-1b completes five. If it all sounds a bit confusing, look at the video below and it will make more sense

SYSTEM Sounds got the advantage of the harmony in the TRAPPIST-1 system and sonified the planets orbiting their star. In the audio, first, you hear each planet completing one orbit as a piano note. Then to emphasise the orbit resonance, the team added a drum sound when the planets matched in orbit. The result is a super cool song.

Created by Matt Russo, Dan Tamayo and Andrew Santaguida 2017.

This type of project shows a new perspective and a new way of looking at data. Much more than just taking photos and looking that them, this is a way to showcase the many nuances and differences often present in astronomic data. Furthermore, this work is excellent to include visually impaired people in astronomical observation, making the cosmos accessible for those who can’t see it. If you have a friend suffering from visual impairment who would like to know what space is like — here’s your chance to show them.

A collection of sonification is found in the Chandra X-ray Center’s ‘A Universe of Sound‘ and SYSTEM Sounds.

The first indirect detection of gravitational waves: the road to LIGO

Gravitational waves are disturbances in space-time generated by some of the largest and most energetic events in the universe. They propagate as waves from a source at the speed of light.

Artistic depiction of gravitational waves. Image credits: Charly W. Karl.

In Einstein’s general theory of relativity, gravity is considered a curvature of spacetime — a curvature caused by the presence of mass. The larger and more compact the mass is, the greater the curvature. For physicists, gravitational waves are also the wave-like solution of Einstein’s equations and the only way through which some phenomena in the universe can be observed.

For instance, when the orbits of two massive bodies change over time, this seemingly results in a loss of energy. But energy can’t be lost, so it must go somewhere — and the only way to explain that loss is that the energy is used to produce waves in space-time, emitting gravitational radiation.

The theory lined up well, but there was a problem: for decades, researchers couldn’t truly detect these gravitational waves, and without validation, the theory couldn’t be confirmed. That all changed in 2015, with the first gravitational waves (GW150914) being directly observed by the two Laser Interferometer Gravitational Wave Observatory (LIGO) detectors. Three years later, the three main scientists behind the detection received the Nobel Prize for the discovery. But researchers may have discovered gravitational waves way earlier, in 1982.

Hulse–Taylor binary

This image shows pulsed gamma rays from the Vela pulsar as constructed from photons detected by Fermi’s Large Area Telescope. Credits: Goddard Space Flight Center.

In 1974, two astrophysicists, (Russell Alan Hulse and Joseph Hooton Taylor Jr) were carrying out a pulsar survey at the Arecibo Observatory, a radio telescope with a 305 meter (1,000 ft) dome. You may remember Arecibo as that big telescope that collapsed to rubble in late 2020 due to underfunding and neglect. Pulsars are a type of compact stars that emit radio or X-ray radiation — they’re a sort of cosmic lighthouse that spins, and whenever it emits a signal towards the Earth, we can detect.

There’s an important reason why Arecibo was so big. The goal of radio telescopes is to detect radio waves — waves for which the wavelength can measure even more than the Earth’s radius. The sources of radio waves outside the solar system are really weak, so we need very big dishes to detect those objects — and Arecibo successfully detected something.

The scientists detected a ‘weird’ pulsar, later named PSR B1913+16 or the “Hulse-Taylor binary”. Researchers noticed that the pulsation period of this pulsar is not stable — it changes and returns to the original state every 7.75 hours. The only explanation for that change was that the pulsar is in a binary system, the pulsar was completing an orbit every 7.75 hours. They knew that thanks to the Doppler effect.

When a light source is moving away from us, its frequency is shifted to the red side of the visible spectrum — and when it moves towards us it is shifted to blue. By measuring the pulsar period, Taylor and Hulse were able to plot a velocity curve to help analyze the orbit and try to figure out who was the pulsar’s companion.

Two stars of different sizes orbiting the same center of mass. The spectrum can be seen to split depending on the position and velocity of the stars. The shift of Star A is greater than that of Star B because the tangential velocity is higher. The line width of Star B is greater than that of Star A because Star B is larger and more luminous. Wikimedia Commons

In their analysis, they observed that system does not have a circular orbit but an ellipse. In the end, they concluded the pulsar lived in a binary system with another compact star, but they could yet not conclude if it was also pulsar or not.

Gravitational waves

By now, you’re probably wondering what this all has to do with gravitational waves. We’re almost there.

Eight years later, without stopping the observations, Taylor and Joel M. Weisberg realized the orbital velocity was increasing, meaning the stars were accelerating. They had also improved their knowledge of the system and figured that both stars have nearly the same mass of 1.4 solar masses and that their orbit is tight, around 4.5 times the Sun’s radius (or 9 times the distance from the Earth to the Moon). The pulsar’s companion is probably another pulsar, they concluded, but we just cannot get its radio signal because the beams it emits are never pointed towards Earth.

The binary was the perfect candidate to test the gravitational waves solution to Einstein’s equations, but because we couldn’t get direct information from the waves themselves, Taylor and Weisberg used theory to indirectly connect the observations from the pulse’s period. They noticed that the orbital period between the stars was decreasing with time, which means it was losing energy — presumably to gravitational waves.

While Arecibo was still working, the observations continued, and 30 years later, the same theory continued to fit the estimated loss of the orbital period, hinting more and more that the binary is emitting gravitational waves. The jaw-dropping conclusion of the study is the almost perfect agreement between the points (in red below) and the theory (blue line) almost as if there isn’t a minimal mistake in Einstein’s theory. Although they didn’t have any direct observation, astronomers had most likely detected gravitational waves indirectly.

Orbital decay of PSR B1913+16.The data points indicate the observed change in the epoch of periastron with date while the parabola illustrates the theoretically expected change in epoch according to general relativity.

The discovery of the binary pulsar resulted in a Nobel prize in 1993 for Taylor and Hulse, but not for the gravitational waves indirect detection. PSR1913+16 has always been the observation that paved the way for the gravitational waves interferometer, with the binary it was almost certain that the theory was correct, scientists just needed to be lucky enough to observe the phenomenon. It happened and in 2017, the Nobel prize in physics was awarded to LIGO researchers for the first solid detection.

The Arecibo Observatory in Puerto Rico. Credit: NAIC Arecibo Observatory, a facility of the NSF

The Arecibo radio telescope collapsed a year ago. The iconic telescope that made the first detection of binary pulsars, and many others, fell to rubble as it struggled to obtain funding in recent years. The data collected by the telescope is still used by scientists, the most recent was published exactly one year after its collapse, the research tries to understand the history of galaxies with their stellar mass.

What is the Oort cloud: the very edge of the solar system

Every system needs a boundary, and the Solar System is no different. Although we haven’t been able to physically reach and see it, we have a theory about what this edge looks like. And its name is the Oort cloud.

The hypothetical structure of the Oort cloud: an inner, disk-shaped cloud surrounded by a spherical outer structure. Image credits Pablo Carlos Budassi via Wikimedia.

Ask anyone on the street where the Solar System ends, and they’re likely to mention Pluto. To a certain extent, it wouldn’t be wrong; Pluto really is one of the farthest planets / dwarf planets from the Sun; as of early 2021, the farthest object in the Solar System is Farfarout . But if we want to be all sciency about it — and we do — the Solar System arguably ends where our star’s gravitational influence becomes too weak to capture and hold objects. In other words, it spans over all the space where the Sun is the dominating tidal force (Smoluchowski, Torbett, 1984). Exactly what constitutes the edge of the Solar System is still up to some debate, however, and some sources — including this post by NASA — consider the space beyond the heliosphere as being ‘interstellar space’.

For the purposes of this post, however, we’ll take the volume where the Sun’s gravity reigns supreme as being the Solar System. The point where that influence ends is far, far away from Earth. So far away, in fact, that we’ve never been able to actually see it, and, realistically speaking, there’s no way humanity will reach there while any of us reading this are still alive. But we do have some theories regarding what goes on out there.

The boundary of the Solar System is marked by a hypothetical structure known as the Oort cloud. We estimate that it is a truly vast expanse filled with varied clusters of ice, from innumerable tiny chunks up to a few billion planetesimals of around 20 kilometers (12 mi) in diameter. There are likely a few rocky or metallic asteroids here, as well, but not many in number. The material in the Oort cloud was likely drawn to its current position through the gravitational influence of the gas giants — Jupiter, Saturn, Neptune, and Uranus — in the early days of the Solar System.

All in all, it is one of the most exciting places humanity has not yet reached.

So what is it?

The thing to keep in mind here is that the Oort cloud is a hypothetical structure. We haven’t yet seen it, nor do we have any direct evidence of it being real. But its existence would fit with other elements and phenomena we see in the Solar System, and it does fit our theoretical understanding of the world around us, as well.

The Oort cloud is a vast body. Since it’s a theoretical structure, there’s quite a bit of uncertainty in our estimates of its size. Still, we believe it stretches from around 0.03 to 0.08 light-years from the Sun, although other estimates put its outer boundary at 0.8 light-years from the Sun. There are also estimates that place it between 1.58 and 3.16 light-years away from the Sun. Needless to say, we don’t have a good handle on exactly where it is, and how large it is.

“It is like a big, thick-walled bubble made of icy pieces of space debris the sizes of mountains and sometimes larger. The Oort Cloud might contain billions, or even trillions, of objects,” NASA explains.

But to give you a rough idea of the distances involved, however, we’ll use Voyager 1, the fastest-going probe we’ve ever sent to space, and the one currently farthest away from Earth. On its current course and acceleration, Voyager 1 would reach the Oort cloud in around 300 years; it would take it some 30,000 years to pass through the cloud (depending on its actual dimensions).

Voyager 1. Image credits NASA via Global Panorama / Flickr.

Still, don’t get too excited. None of the space probes humanity has launched so far will still be operational by the time they reach the Oort cloud; despite being powered by RTGs, a type of nuclear battery, all of these crafts will run out of power far before they reach the Oort clour.

Why do we think it’s a thing?

The concept of the Oort cloud was first suggested in the 1930s by Estonian astronomer Ernst Öpik. The idea was cemented in the 1950s when its existence was independently suggested a second time by Jan Oort, a Dutch astronomer. Because of this dual origin, it is sometimes referred to as the Öpik–Oort cloud.

The existence of this cloud was proposed mainly due to comets — long-period and Halley-type comets, to be precise. Since comets coming close to the Sun lose part of their volatile contents (for example water) under the influence of solar radiation, logic dictates that they must form away from the star. At the same time, gravitational influences would see them either collide with a planet or star or be ejected from the Solar System eventually — meaning that their ‘lifespan’ is limited. Since there are still comets zipping around the Sun, this means that there must be a reservoir of comets to be drawn towards our star.

Put together, both of these point to the existence of a cloud-like formation at the very edge of the Sun‘s gravitational influence populated with comet-like bodies — the Oort cloud.

Short-period comets orbit around the Sun every few hundreds of years; because of this short time, it’s generally accepted that they originate from structures closer to Earth, such as the Kuiper belt (a field of asteroids extending past Neptune). Long-period comets, however, can have orbits lasting thousands of years. The only source that could explain such huge spans of time is the Oort cloud. One exception to these rules is Halley-type comets. Although they are short-period comets, we believe they’re originally from the Oort cloud and that they’ve been pulled ever closer to the center of the Solar System under the gravitational effects of the Sun and inner planets.

What are we doing to study it?

The main impediment to our studying of the Oort cloud is distance. It’s simply too far away for our spaceships or probes to reach in any practical manner. There also haven’t been any direct observations of the Oort cloud.

Despite this, its existence is widely accepted in academic circles. Researchers rely on indirect methods of study to peer into the secrets of the Oort cloud. These revolve heavily around the study of comets and their properties. There is also a lot of effort being poured into developing devices and methods that can be used to spot individual bodies inside the Oort cloud. This is no easy feat, as they’re quite tiny by cosmological standards, and very far away.

Once we do have such tools at our disposal, however, astronomers will finally be able to confirm whether the Oort cloud actually exists. It’s very likely that it does, and it would fit with our current understanding of the Universe. But until we can see it, we won’t be able to tell for sure.

The longest lunar eclipse in nearly 600 years is happening tonight

An almost total lunar eclipse is expected overnight this Thursday, November 18th, to Friday, November 19th. It will last almost three hours and 30 minutes, making it the longest in centuries. About 97% of the moon will vanish into Earth’s shadow – visible in many parts of the world, including North and South America and eastern Australia.

Lunar eclipses happen when the Earth, the Moon, and the Sun align so that the Moon passes into Earth’s shadow. There are three types – total, partial and penumbral. In a total eclipse, which is the most dramatic, Earth’s shadow, called the umbra, covers up to 99.1% of the Moon’s disk. We’ll be very close to seeing that this night. 

During the eclipse, the moon should have a reddish-brown color as it slips into the shadow, a phenomenon called Rayleigh scattering — the same mechanism which makes sunsets look red and the sky look blue. The Moon’s level of red will depend on the dust or clouds in the atmosphere of Earth during the eclipse.

“Partial lunar eclipses might not be quite as spectacular as total lunar eclipses — where the moon is completely covered in Earth’s shadow – but they occur more frequently,” NASA said in a skywatching update. “And that just means more opportunities to witness little changes in our solar system that sometimes occur right before our eyes.”

A remarkable experience

The eclipse will be visible in several parts of the world across the evening of Thursday and into early Friday. The exact time will depend on each location, with a few websites around in which you can get your exact times. But it will likely be a long night. For example, in New Mexico, it will start at 12.18am and reach its maximum at 2.02am. 

A world map showing where the eclipse is visible at the time of greatest eclipse. Earlier parts of the eclipse are visible farther east, while later times are visible farther west. Image credit: NASA.

In case you don’t want to stay up late or watch the eclipse in person, there are also online options. The Virtual Telescope Project (VTP) is doing a special broadcast of the eclipse starting at 11 pm PT on Thursday. VTP also partnered up with astronomers from around the world and will offer a live commentary from astrophysicist Gianluca Masi. 

The last time a lunar eclipse took place was on May 26, 2021, named the “super flower blood moon.” It was a total eclipse, the first one since 2019, and it was visible in its entirety over Oceania and the Pacific Ocean. Those in southern and eastern Asia could see it at moonrise, while those in North and South western America saw it at moonset. 

Eclipses have caused inspiration but also fear across history, especially when the moon turns blood-red, as earlier in May this year. They don’t happen a lot and aren’t always visible. But they are a remarkable experience worth watching, allowing us to admire how the Sun, the Earth and the Moon are all connected as part of the solar system. 

Neutron Stars: one of the most extreme objects we know

Neutron stars are one of the most amazing things we know of in the universe. A teaspoon of neutron star material would weigh around a billion tons, making them some of the densest objects in the universe, second only to black holes. Aside from being extremely dense, they can emit bizarre pulses, and sometimes, they form in binary systems — where things can get even wilder.

The gas comprising the disk orbits around and gradually spirals onto the neutron star. Credits: Wagoner (2003).

In 1969, Jocelyn Bell detected the first neutron star. She was a PhD student at Cambridge University and detected a very powerful and extremely regular radio pulse (which was later named a pulsar). It was so eerily regular that the signal’s first nickname was LGM-1, “Little Green Men 1”.

The people who later got involved in the study didn’t really believe it was another civilization and set out to find the signal’s underlying cause. They found it to be a neutron star, the collapsed core of a massive supergiant star that wasn’t quite massive enough to turn into a black hole.

Today, we can detect neutron stars by looking at their signals with X-ray detectors, and we’ve learned quite a lot about them.


Neutron stars are born when a star with 8 to 20 solar masses runs out of fuel. The star undergoes a number of nuclear fusion reactions which leave behind a layered onion shape, including a core made of iron. The iron core is the key to how the star will develop; if the core’s mass is above a limit (called the Chandrasekhar limit), the star will collapse into a neutron star or black hole. Stars with masses lower than this limit will remain stable as white dwarfs.

The formation of a neutron star can happen at dazzling speed. A supernova occurs within 0.1 seconds and what is left behind from the primary star is just its core, which is now made out of neutrons. The explosion releases neutrinos which are antisocial particles that don’t interact with almost any other particles.

A neutron star begins its life as a star between about 7 and 20 times the mass of the sun. When this type of star runs out of fuel, it collapses under its own weight, crushing its core and triggering a supernova explosion. What remains is an ultra-dense sphere only about the size of a city across, but with up to twice the mass of the sun squeezed inside. Credits: NASA/NICER.

In 1987, a supernova exploded and we detected neutrinos from outside of the solar system for the first time in the Kamiokande detector. 

The neutron star left from the colossal boom has nearly 1.5 solar masses, but its radius is just around 10 kilometres, making it the densest star in the universe we know of –  one tablespoon of a neutron star contains billions of kilograms. Mostly made of neutrons, of course, but also with some protons and electrons here and there, without the extra particles it wouldn’t be stable enough, the neutrons could decay into protons and electrons.

Interestingly though, neutron stars don’t collapse on themselves despite their massive gravitational attraction and are generally stable.

This happens because neutrons are essentially fermions, subatomic particles that respect their own personal space; you could say they practice subatomic social distancing.

In more scientific terms, fermions obey the Pauli exclusion principle: “you can’t have identical fermions in the same quantum state”. This means the identical neutrons can’t occupy the same space, thus, the pressure from ‘trying to avoid other neutrons’ personal space’ competes against gravity and the neutron star keeps itself stable for a long time. This type of matter is often referred to as “degenerate matter” — a highly dense state of fermionic matter in which the Pauli exclusion principle exerts enough pressure (in addition to, or in lieu of thermal pressure) so that the neutron star doesn’t collapse.

Classifying neutrons stars

There are several ways to classify neutron stars, but commonly, there are three types of neutron stars.

The easiest ones to find are the pulsars. Pulsars are highly magnetized rotating neutron stars that emit beams of electromagnetic radiation from their magnetic poles. They have a highly periodic pulse, which can repeat a cycle within milliseconds or over several seconds. The rotation and the beam don’t necessarily need to be aligned, that’s why most images illustrating pulsars show the tilted version of the cycles.

Credits: NASA/JPL-Caltech.

Pulsars are very serious about their timing — so much so that astronomers sometimes use them as celestial timekeepers. The timing from their pulses can be used to precisely find objects, just like how sailors of yore used stars to guide themselves at sea. The Voyager spacecraft has a message to any civilization to find Earth. How did they map it? With radio pulsars. The positions of galactic pulsars are placed on a scale in the map with their number of rotations per cycle dashed along the lines.

Another neutron star is the magnetar, and here, things really get extreme. Pulsars are already extreme objects with titanic magnetic fields, but the magnetars have fields 1000 stronger than even that of a pulsar. To get an idea of how big a field we’re talking about, the Large Hadron Collider has magnets to help accelerate particles, and its magnetic field is around 8.3 Tesla. Magnetar’s magnetic field is 10,000,000 billion Tesla. They can also cause giant flares, and release energy 100,000,000 billion times stronger than a solar flare.


Neutron stars can orbit a companion, sometimes a white dwarf, sometimes a main-sequence star, or even another neutron star. Things get weird when they start to merge. 

This animation captures phenomena observed over the course of nine days following the neutron star merger known as GW170817. They include gravitational waves (pale arcs), a near-light-speed jet that produced gamma rays (magenta), expanding debris from a kilonova that produced ultraviolet (violet), optical and infrared (blue-white to red) emission, and, once the jet directed toward us expanded into our view from Earth, X-rays (blue).
Credits: NASA’s Goddard Space Flight Center/CI Lab
Download this video in HD formats from NASA Goddard’s Scientific Visualization Studio

On 2017 August 17, both the Virgo and Laser Interferometer Gravitational-Wave Observatory (LIGO) teams detected two neutron stars merging gravitational waves in another galaxy called the GW170817. Because the merging process was so catastrophic, the event emitted gamma rays detected by the Fermi Gamma-ray Space Telescope. There were also visual signals from that event and other important measurements, multi-messenger observations, something widely anticipated as the future of astrophysics.


Remember the Pauli exclusion principle? Well, we’re not done with it just yet. There is a phase of matter which is like a fluid but not really, and it works in the same way as the superconductors.

This stylized animation shows the structure of a neutron star. The states of matter within neutron stars’ inner cores remains a mystery.
NICER will confront nuclear physics theory with unique measurements, exploring the exotic states of matter within neutron stars through rotation-resolved X-ray spectroscopy. Credits: NASA/Nicer.

When you try to join particles with the same charge they repel each other. But at a very specific temperature and in the case of neutron stars, density, they can get along and ignore the social distancing. Superconductors have a weird mechanism to form interactions between electrons, the Cooper pairs. These interactions make the superconductor have zero resistivity, for a superfluid, it means zero viscosity, a property in fluids that make them flow slowly. 

Neutrons aren’t supposed to form pairs either, even though they aren’t charged. However, in that extreme environment, they manage to form this superconducting phase that is actually called a superfluid state. It happens inside the neutron star’s inner crust and outer core.

The Cooper pairs made of neutrons make a superfluid state possible in a neutron star. It may sound weird to call it fluid in such a dense object, but if you think about it is not a problem, everything is dense, and the core is denser, a less dense region compared to a super dense one can be called a fluid.

The evidence for that is the result of the pairing. The relationships between neutrons aren’t stable so they break up and emit neutrinos in response, this neutrino release makes the star cool down. Two groups independently detected the cooling mechanism from the neutron star inside the Cassiopeia A. The 10-year observation shows that the star cooled 4%, the best explanation is that it agrees with the superfluid theory. 

Cassiopeia A. Image credit: NASA/CXC/SAO.

That was just a few of the quirky characteristics of neutron stars, they can get weirder than that. Exotic stuff probably happens in their inner cores, explained with more quantum mechanics which could make ‘Rick and Morty’ seem old hat.

Astronomers discover the fastest orbiting asteroid

Astronomers have discovered a one-kilometre wide asteroid orbiting the Sun at a distance of just 20 million km (12 million miles). Not only does this make the asteroid–currently designated 2021 PH27–the Sun’s closest neighbour, but it also means that as it completes an orbit in just 113 days, it is also the solar system’s fastest-orbiting asteroid. 2021 PH27 skirts so close to the Sun that its discoverers say its surface temperature is around 500 degrees C–hot enough to melt lead.

An artist’s rendition of the asteroid 2021 PH27 inside Mercury’s orbit. (CTIO/NOIRLab/NSF/AURA/J. da Silva)

Scott S. Sheppard of the Carnegie Institution of Science first spotted asteroid 2021 PH27 in data collected by the Dark Energy Camera (DECam) mounted at the prime focus of the Victor M. Blanco 4m Telescope at Cerro Tololo Inter-American Observatory (CTIO), Chile. Brown University astronomers Ian Dell’antonio and Shenming Fu took images of the asteroid on 13th August 2021 at twilight–the optimum time for hunting asteroids that lurk close to the Sun. Just like the inner planets–Mercury and Venus–asteroids that exist within the Earth’s orbit become most visible at either sunrise or sunset.

The discovery was followed by measurements of the asteroid’s position conducted by David Tholen of the University of Hawai‘i. These measurements allowed astronomers to predict asteroid 2021 PH27’s future position, leading to follow-up observations on the 14th of August by DECam and the Magellan Telescopes at the Las Campanas Observatory in Chile.

The Víctor M. Blanco 4-meter Telescope at the Cerro Tololo Inter-American Observatory (CTIO) home to the Dark Energy Camera (DECam) (CTIO/NOIRLab/NSF/AURA/R. Sparks)

These observations were then subsequently followed on August 15th by imaging made with the Las Cumbres Observatory network of 1- to 2-meter telescopes located in Chile and South America by European Space Agency (ESA) researcher  Marco Micheli.

The findings were so significant that many astronomers cancelled their scheduled projects to use telescope time with a variety of sophisticated instruments to further observe the asteroid. “Though telescope time for astronomers is very precious, the international nature and love of the unknown make astronomers very willing to override their own science and observations to follow up new, interesting discoveries like this,” explains Sheppard.

What makes the discovery of asteroid 2021 PH27 so special, and of great interest to astronomers, is the fact that it belongs to a population of solar system bodies that have been, thus far, notoriously difficult to spot.

Hunting For Inner Solar System Asteroids

Interior asteroids that exist close to the Sun tend to be difficult for astronomers to spot because of the glare from our central star. This difficulty is amplified by the fact that as they get close to the Sun these objects experience intense gravitational, tidal, and thermal forces that breaks them up into smaller–thus tougher to spot–fragments.

The fastest orbital period asteroid in the Solar System has been discovered at NOIRLab’s CTIO using the powerful 570-megapixel Dark Energy Camera (DECam) in Chile — the Sun’s new nearest neighbour. The asteroid was imaged inside Mercury’s orbit and has been coloured red and blue to show the two different times where it was imaged on the discovery night of 13 August 2021 — just three minutes apart. (CTIO/NOIRLab/NSF/DOE/DECam/AURA/S.S. Sheppard (Carnegie Institution of Science)

That means tracking an intact interior asteroid could have benefits for our understanding of these objects and the conditions they experience. In particular, if there are few asteroids experiencing a similar orbit to asteroid 2021 PH27 it may indicate to astronomers many of these objects were loose ‘rubble piles.’ This may, in turn, give us a good idea of the composition of asteroids on a collision course with Earth, and crucially, how we could go about deflecting them.

“The fraction of asteroids interior to Earth and Venus compared to the exterior will give us insights into the strength and make-up of these objects,” Sheppard continues. “Understanding the population of asteroids interior to Earth’s orbit is important to complete the census of asteroids near Earth, including some of the most likely Earth impactors that may approach Earth during daylight and that cannot easily be discovered in most surveys that are observing at night, away from the Sun.”

In addition to this, asteroid 2021 PH27’s orbit is so close to the Sun that our stars exerts considerable gravitational effects upon it, something that could make it a prime target for the study of Einstein’s geometric theory of gravity–better known as general relativity.

This close proximity to the Sun may actually be a recent development for asteroid 2021 PH27.

Asterod 2021 PH27 is on the Move

Planets and asteroids don’t move around their stars in perfectly circular orbits, but in ellipses–flattened out circles. The ‘flatter’ the circle the greater we say its eccentricity is. The widest point of the ellipse is the semi-major axis and for an orbit, this represents the point at which a body is farthest from its parent star.

Asteroid 2021 PH27 has a semi-major axis of 70 million kilometres (43 million miles or 0.46 au) which gives it a 113-day orbit crossing the orbits of both Venus and Mercury. But it may not have always existed so close to the Sun.

The fastest orbital period asteroid in the Solar System has been discovered at NOIRLab’s CTIO using the powerful 570-megapixel Dark Energy Camera (DECam) in Chile — the Sun’s new nearest neighbour. The illustration shows the locations of the planets and asteroids on the discovery night of 13 August 2021, as they would be seen from a vantage point above the Solar System (north). (CTIO/NOIRLab/NSF/AURA/J. da Silva)

Astronomers believe that the asteroid may have started life in the main asteroid belt between Mars and Jupiter, with the gravitational influence of the inner planets drawing it closer to the Sun. This would make it similar to the Near-Earth Object (NEO) Apophis, which has only recently been ruled out as a potential Earth impactor, which was also dragged closer to the Sun by gravitational interactions.

There is also some evidence arising from 2021 PH27’s high orbital inclination of 32 degrees that the asteroid may have a slightly more exotic origin, however. This could imply that the asteroid is actually an extinct comet that comes from the outer edge of the solar system pulled into a close orbit as it passed an inner-terrestrial–rocky–planet. Astronomers will be looking to future observations to determine which of these origins is correct, but unfortunately, this will have to wait. 2021 PH27 is about to enter solar conjunction which means that from our vantage point on Earth it is about to move behind the Sun. That means the asteroid will only become available for further observations in 2022.

These follow-up observations will allow astronomers to better determine its orbit. And with this better determination will come a new official name that is hopefully a bit less of a mouthful than 2021 PH27. But what is certain is that this asteroid is not set to become any less interesting.

What is gravitational lensing — and how it helped prove Einstein right

In 1915, a physicist by the name of Albert Einstein published a theory that managed to connect the curvature of space-time with energy. It is called General Relativity, and Einstein focused on it as a way to bring gravity into his previous special relativity work.

The theory of general relativity says that the gravitational attraction between objects’ masses comes from their warping of spacetime. Armed with this insight, general relativity was able to predict many things, including the most famous confirmation that gravitational waves exist. But for around a long time, there was no direct proof. The first direct proof came from gravitational lensing.

Gravitational pull distorts the space-time continuum around them.

As we were discussing, energy and time-space curvature are related. The most massive objects are capable of curving space-time itself. Think of a ball on a stretched sheet: the ball curves the sheet, and if you let a smaller object slide on that sheet, it will move towards the ball. 

The surprise is that something absurdly massive can even bend light. Yes, light, the fastest thing to carry information in the universe, can be bent — sort of. That is the ‘innovative’ thing about general relativity, the theory allows even objects which are massless to be affected by gravity. Photons are the particles that constitute light and they have zero mass, thus light can be deformed in the presence of a strong gravitational field.

How it works — and what do lenses have to do with it

The fact that lenses can distort images does not need relativity at all. A glass filled with water can distort light behind or inside the glass. In photographic lenses, if not corrected, images are curved and don’t look realistic.

Scientists have been aware of lenses and their effects for a long time, but with the advent of telescopes, they also realized that objects with very large masses (some stars, galaxies, black holes) distort light in a similar way to lenses here on Earth. So these celestial objects can be used as a sort of lens — a gravitational lens.

When the lens and the target are close enough (from an astronomical perspective) and closely aligned, multiple images can be formed, appearing in an arc shape — this is called strong lensing. The image multiplication of a light source can be out of sync due to the curvature of space. Some images will take longer to reach the observer because the light is taking a longer path.

Hubble Space Telescope image of LRG 3-757. An orange foreground galaxy gravitationally lenses a blue background galaxy. The near alignment of the two objects in the sky causes the blue background galaxy (the source) to appear as an Einstein ring. (Image courtesy of NASA/European Space Agency/Hubble.)

When lens and source are in nearly perfect alignment the image deforms to a ring shape, called Einstein–Chwolson ring. The most famous multiple image phenomena are the so-called “Einstein crosses” — where the image of a single source is deformed into a cross shape, four more versions of the target appear due to the gravitational phenomenon.

Einstein cross. Credits: Universe Today.

Meanwhile, weak lensing happens when the image is distorted, but without any copies of the target — just a distortion of it with elongated shapes. Microlensing, on the other hand, has to do with motion, either the source, the lens or us. The motion changes the source’s magnification making objects which are usually hard to observe brighter.

Gravitational microlensing. Credits: Grzegorz Pietrzyński.

Proving Einstein right

Gravitational lensing was one of the key techniques used to prove General Relativity. In 1919, a solar eclipse was observable in some countries in the Southern Hemisphere and the Hyades star cluster happened to be in the same view range as the Sun. Sir Frank Watson Dyson sent two expeditions in different locations of the globe to observe the eclipse — coincidentally, two Portuguese-speaking places — one in the Democratic Republic of São Tomé and Príncipe (at the time called ‘the island of Príncipe’, with Arthur Eddington and Edwin Cottingham, and another in the city of Sobral in Brazil with Charles Davidson and Andrew Crommelin. 

The team at Sobral found better weather conditions and registered 7 images in contrast to the Príncipe team’s only 2 images. Later, the analysis of the photographic plates was carried out by estimating the deflection angle from the two experiments. With both results, considering the error bar, the observation confirmed the theory. Despite the evidence, the confirmation did not give Einstein immediate prestige. Other eclipses had to help and the scientific community took time to digest the theory. 

Photograph of the solar eclipse by Arthur Eddington and Edwin Cottingham, Príncipe, 29 May 1919. Credits: Royal Astronomical Society.

What can we find with gravitational lensing?

Lensing effects don’t occur when there is a star or a galaxy in our view range. Dark matter is massive, therefore has a gravitational field. Scientists use gravitational lensing to estimate the amount of dark matter from giant galaxy clusters.

This Hubble Space Telescope composite image shows a ghostly “ring” of dark matter in the galaxy cluster ZwCl0024+1652. Credits: NASA, ESA, M.J. Jee and H. Ford (Johns Hopkins University).

Microlensing can help astronomers/astrophysicists find exoplanets. When a lens is passing in front of a star, its brightness will have a maximum in perfect alignment and as the motion continues it returns to the original magnification. Every time the star is being eclipsed by a planet, anomalies in the brightness evolution will appear and the researchers can confirm the presence of a host planet.

Finding exoplanets with microlensing. Credit: NASA, ESA, and K. Sahu (STScI).

Remember the Cosmic Microwave Background (CMB)? It is the oldest ‘image’ of the universe, when photons could travel freely without interaction with matter. Photons are light, everything on light’s path can bend it. Scientists can know how distorted the CMB is by analyzing dark matter.

The Planck Satellite was the first instrument to give results on the distribution of dark matter in the universe through gravitational lensing. In the image illustrating this distribution, the gray color is to represent the Milky Way and very bright nearby galaxies; they need to be excluded because they mess with the measurements. Dark blue are regions with more dark matter than the bright portions.

All-sky map of dark matter distribution in the Universe. Credits: ESA and the Planck Collaboration.

If you expect a certain amount of effort, if not struggle just to detect a few galaxies, scientists are already thinking of lensed gravitational waves. How hard could that be, right? They predict a boost in gravitational waves’ signal if they are amplified by strong lensing. The problem is that it also helps increase the noise/errors in the observations. Until then, a lot of work is being done with gravitational lensing, something that came from a very abstract theory, proving theoretical work deserves respect.

InSight maps Mars’ composition and chunky core for the first time

We are closer than ever before to understanding the composition of Mars thanks to the first observations of seismic activity on the planet made by the InSight lander. The NASA-led project, which landed on the surface of the Red Planet in November 2018 with the goal of probing beneath the Martian surface, observed several so-called ‘marsquakes’ which reveal details about its crust, mantle, and core.

Using seismic activity or ‘marsquakes’ researchers have detailed the composition of the Martian interior for the first time (Cottaar/ Science)

InSight’s primary findings which are detailed in three papers published today in the journal Science, represent the first time scientists have been able to produce a detailed picture of the interior of a planet other than Earth.

“We are seeking to understand the processes that govern planetary evolution and formation, to discover the factors that have led to Earth’s unique evolution,” says Amir Khan, ETH Zurich and the University of Zurich, whose team used direct and surface reflected seismic waves to reveal the structure of Mars’ mantle. “In this respect, the InSight mission fills a gap in the scientific exploration of the solar system by performing an in-situ investigation of a planet other than our own.”

The results from the ongoing NASA mission–with the full title ‘Interior Exploration using Seismic Investigations, Geodesy and Heat Transport’— could reveal key insights into the Red Planet‘s formation and evolution, as well as helping us understand the key differences between our planet and Mars.

“One big question we would like to understand is why Earth is the only planet with liquid oceans, plate tectonics, and abundant life?” adds Khan. “Mars is presently on the edge of the solar system’s habitable zone and may have been more hospitable in its early history. Whilst we don’t yet know the answers to these questions, we know they to be found are on Mars, most likely within its interior.”

The InSight Lander on the surface of Mars ((NASA/JPL-Caltech))

InSight first detected the presence of marsquakes from its position in Elysium Planitia near the Red Planet’s equator in 2019 and has since picked up more than 300 events–more than 2 a day–tracing many of them back to their source.

What is really impressive is what researchers can do with these quakes, using them as a diagnostic tool to ‘see’ deep into the planet’s interior.

“Studying the signals of marsquakes, we measured the thickness of the crust and the structure of the mantle, as well as the size of the Martian core,” Simon Stähler, a research seismologist at ETH Zurich, tells ZME Science. “This replicates what was done on Earth between 1900 and 1940 using the signals of earthquakes.”

From the Crust of Mars…

The observations made by InSight have allowed researchers to assess the structure of Mars’ crust, allowing them to determine its thickness and other properties in absolute numbers for the first time. The only values we previously had for the Martian crust were relative values that showed differences in thickness from area to area.

“As part of the bigger picture on the interior structure of Mars, we have determined the thickness and structure of the Martian crust,” Brigitte Knapmeyer-Endrun, a geophysicist at the University of Cologne’s Institute of Geology, tells ZME Science. “Previous estimates could only rely on orbital data–gravity and topography–that can accurately describe relative variations in crustal thickness, but no absolute values. These estimates also showed a wide variability.”

The Mars InSight lander’s seismometer consists of a protective dome that contains three extremely sensitive sensors. (NASA/JPL-Caltech)

With data collected regarding the crustal thickness at InSight’s landing area, new seismic measurements, and data collected by previous missions, the team could map the thickness across the entire Martian crust finding an average thickness of between 24 and 72 km.

Knapmeyer-Endrun explains that the data she and her team collected with InSight’s Seismic Experiment for Interior Structure (SEIS), particularly the very broad-band (VBB) seismometer–an instrument so sensitive it can record motion on an atomic scale–and information from the Marsquake Service (MQS) at ETH Zurich, suggest that the Red Planet’s crust is thinner than models have thus far predicted.

“We end up with two possible crustal thicknesses at the landing site–between 39 and 20 km– but both mean that the crust is thinner than some previous estimates and also less dense than what was postulated based on orbital measurements of the surface.”

Knapmeyer-Endrun continues by explaining that the InSight data also reveals the structure of the Martian crust as multi-layered with at least two interfaces that mark a change in composition. In addition to this, the team can’t rule out the presence of a third crustal layer before the mantle.

“The crust shows distinct layering, with a surficial layer of about 10 km thickness that has rather low velocities, implying that it probably consists of rather porous–fractured–rocks, which is not unexpected due to the repeated meteorite impacts,” says the geophysicist adding that we see something similar on the Moon, but the effect is more extreme due to that smaller body’s much thinner atmosphere.

The two largest quakes detected by NASA’s InSight appear to have originated in a region of Mars called Cerberus Fossae. Scientists previously spotted signs of tectonic activity here, including landslides. This image was taken by the HiRISE camera on NASA’s Mars Reconnaissance Orbiter (NASA/JPL-Caltech/University of Arizona)

Knapmeyer-Endrun is pleasantly surprised regarding just how much information InSight has been able to gather with just one seismometer.”It’s surprising we were really able to pull all of this information about the interior of Mars from the recordings of quakes with magnitudes of less than 4.0 from a single seismometer,” she explains. “On Earth, we would not be able to even detect those quakes at a comparable distance. We typically use 10s or even 100s of seismometers for similar studies.”

And the marsquake data collected by InSight has not just proven instrumental in assessing the thickness and composition of the planet’s crust, it has also allowed scientists to probe deeper, to the very core of Mars itself.

…To the Martian Mantle and Core

Using direct and surface reflected seismic waves from eight low-frequency marsquakes Khan and his team probed deeper beneath the surface of Mars to investigate the planet’s mantle. They found the possible presence of a thick lithosphere 500km beneath the Martian surface with an underlying low-velocity layer, similar to that found within Earth. Khan and his co-author’s study reveals that the crustal layer of Mars is likely to be enriched with radioactive elements. These elements heat this region with this warming reducing heat in lower layers.

It was these lower regions that Stähler and his colleagues investigated with the use of faint seismic signals reflected by the boundary between the Martian mantle and the planet’s core. What the team discovered is that the Red Planet’s core is actually larger than previously calculated, with a radius of around 1840 km rather than previous estimates of 1600km. This means the core begins roughly halfway between the planet’s surface and its centre.

From the new information, we can also determine the core’s density and extrapolate its composition.

A Comparison of Mars’ Earth’s interiors. The Martian core shown here is smaller than these new findings suggest. Whilst the crust shown is thicker.

“We now know for sure the size of the core and it’s significantly larger than it had been thought to be for a long time,” says Stähler. “Because we found that the core is quite large, we, therefore, know it is not very dense. This means that Mars must have accumulated a substantial quantity of light, volatile elements such as sulfur, carbon, oxygen, and hydrogen.”

This ratio of lighter elements is greater than that found within Earth’s denser core, and it could give us important hints about the differences in the formation of these neighbouring worlds.

“Somehow these light elements needed to get into the core. It may mean that the formation of Mars happened faster than Earth’s,” Stähler says. “These observations have fueled speculation that Mars might represent a stranded planetary embryo that depicts the chemical characteristics of the solar nebula located within the orbit of Mars.”

Thanks to NASA's InSight Mars mission we now have a good picture of the interior of another planet.
InSight captures an image of its landing site, which proved the ideal vantage point to observe marsquakes (NASA)

As just Knapmeyer-Endrun did, Stähler expresses some surprise regarding just how successful InSight has been in gathering seismological data, emphasising the role good fortune has played in the mission thus far.

“We were able to observe reflections of seismic waves from the core–like an echo–from relatively small quakes. And the quakes were just in the right distance from the lander. Had we landed in another location, it would not have worked out,” the seismologist says. “And the landing site was only selected because it was flat and had no rocks, so it was really pure luck.”

Stähler says that he and his team will now attempt to use seismic waves that have crossed the core of Mars to determine if the planet’s core possesses a solid-iron inner-core like Earth, or if it is entirely liquid. Just one of the lingering questions that Knapmeyer-Endrun says InSight will use marsquakes to tackle over the coming years.

“There are still multiple open questions that we’d like to tackle with seismology. For example, which geologic/tectonic features are the observed marsquakes linked to? At which depth do olivine phase transitions occur in the mantle? And Is there a solid inner core, like on Earth, or is the whole core of Mars liquid?” says the geophysicist.

And if we are to go by track record, the smart money is on InSight answering these questions and more. “Within just 2 years of recording data on Mars, this single seismometer has been able to tell us things about the crust, mantle and core of Mars that we’ve been speculating about for decades.”

ESO / L. Calçada

Neutron Stars Make Ant Hills Out of Mountains

The surfaces of neutron stars may feature mountains, albeit ones that are no more than millimetres tall, new research has revealed. The minuscule scale of neutron star mountains is a result of the intense gravity produced by these stellar remnants that are the second densest objects in the Universe after black holes.

Because neutron stars have the mass equivalent to a star like the Sun compressed into a diameter that is about the size of a city on Earth–about 10km– they have a gravitational pull at their surface that is as much as 40,000 billion times stronger than Earth’s.

This presses features on that surface flat, making for almost perfect spheres. Yet the new research, presented at the National Astronomy Meeting 2021 shows that these stellar remnants do feature some tiny topological deformations, analogous to mountains on a planet’s surface.

ESO / L. Calçada
Artist’s rendition of a neutron star. New research suggests mountains on such stellar remnants could be no more than a fraction of a millimetre tall. ESO / L. Calçada

The finding was a result of complex computer modelling by a team of researchers led by the University of Southhampton’s Fabian Gittins. The Ph.D. student’s team simulated a realistic neutron star and then calculated the forces acting upon it. What the research really shows is how well neutron stars can support deviations from a perfect sphere without its crust being strained beyond breaking point.

This revealed how mountains could be created on such dense stellar remnants and demonstrated that such formations would be no taller than a fraction of a millimetre.

“For the past two decades, there has been much interest in understanding how large these mountains can be before the crust of the neutron star breaks, and the mountain can no longer be supported,” says Gittins. These results show how neutron stars truly are remarkably spherical objects. “Additionally, they suggest that observing gravitational waves from rotating neutron stars maybe even more challenging than previously thought”.”

Mountain formation has been formulated for neutron stars before, but these new findings suggest such features would be hundreds of times smaller than the mountains of a few centimetres previously predicted. This is because those older models took the crusts of neutron stars to the edge of breaking point at every single point; something the up-to-date research suggests is less than realistic.

Neutron stars form when massive stars run out of fuel to power nuclear fusion. This means that the toward force balancing against gravity’s inward pull is cancelled and leads to the gravitational collapse of the star. During the course of this collapse, the massive star ejects its outer material in supernova explosions and leaving behind a core of ultradense material. This stellar remnant is only protected from further collapse–and in turn, becoming a black hole–by the quantum mechanical properties of the neutron-rich material that composes it.

An artist’s impression of a pulsar. (Michael Kramer/JBCA/Unversity of Manchester).

The finding may have implications that go beyond the modelling of neutron stars. Tiny deformations on the surface of rapidly spinning neutron stars called pulsars could launch gravitational waves–the tiny ripples in spacetime predicted by general relativity and detected here on Earth by the LIGO/Virgo collaboration.

Unfortunately, as precise and sensitive as the LIGO laser interferometer is, it is still not powerful enough to detect gravitational waves launched by these ant-hill like mountains. It is possible that future upgrades to these Earth-based detectors and advancements such as the space-based gravitational wave detector LISA could make observing the effect of these tiny bumps possible.

Scientists develop AI to identify holes in the Sun’s corona

If you’ve ever seen images of the Sun, you may have noticed some dark marks on the surface of the corona, the aura of plasma that surrounds the Sun and other stars. These dark spots are massive areas that are colder than the surrounding corona — still very hot, mind you, just not as hot as the rest of the corona. Now, astronomers have a new way of identifying them.

The AIA instrument of SDO captured this image of the sun showing an X1.1 class flare on Nov. 8, 2013 . Credits: NASA

Usually, astronomers observe and identify coronal holes using Extreme Ultraviolet (EUV) and X-ray light detectors. However, it is hard to differentiate the dark features which are holes from other dark spots, such as filaments. It’s easy to tell there’s a dark area on the solar corona, but figuring out what that dark spot is not as easy.

Now, a team of scientists developed an artificial neural network called CHRONNOS (Coronal Hole RecOgnition Neural Network Over multi-Spectral-data) to identify the coronal holes. They used data collected by SDO (Solar Dynamics Observatory) NASA satellite, from November 2010 to December 2016, to train and test the model.

The magic of the model lies in giving data with an increasing image resolution. Starting for example, with 8×8 pixels, then 64×64 pixels, and finally 512×512 pixels. This is done to give as much information to the AI and for faster performance, lower-resolution data is easier for the network to analyze. 

As you can see in the video, the team used the timelapse of the last two months of each year from 2010 to 2019. The red contours show the holes over the days with a surprisingly smooth transitional variation.

The new method was successful at detecting 261 coronal holes within that time period with 98.1% of correct detections. The team also compared the relation between the holes detected with sunspots. They have concluded that their model is independent from solar activity, whether it’s in its maximum or minimum. 

The study was published in Astronomy & Astrophysics.

Artist's view of a black hole-neutron star merger. (Carl Knox, OzGrav - Swinburne University)

Neutron Star and Black Hole’s Final Dance Observed for the First Time

Astrophysicists have finally observed the spiralling merger between a neutron star and a black hole. The cataclysmic event was witnessed in a gravitational wave signal by the LIGO/Virgo/KAGRA collaboration and is the first time that one of these elusive but titanic ‘mixed’ merger events has been spotted and had its nature confirmed. And just like buses, you wait for an age for one to come and then two arrive at once.

The researchers also detected a gravitational wave signal from another event of the same nature just ten days after the first, with the signals picked up by LIGO/Virgo on 5th January 2020 and the 15th January 2020 respectively.

The finding is significant because of the three types of mergers between stellar remnant binaries–neutron star/neutron star mergers, black hole/ black hole mergers, and neutron star/ black hole or mixed mergers–this latter category is the only one we hadn’t detected until now and has proved fairly elusive.

 “With this new discovery of neutron star- black hole mergers outside our galaxy, we have found the missing type of binary,” says Astrid Lamberts, a CNRS researcher at Observatoire de la Côte d’Azur, in Nice, France. “We can finally begin to understand how many of these systems exist, how often they merge, and why we have not yet seen examples in the Milky Way.”

Artist's view of a black hole-neutron star merger. (Carl Knox, OzGrav - Swinburne University)
Artist’s view of a black hole-neutron star merger. (Carl Knox, OzGrav – Swinburne University)

These detections of signals from separate mixed merger events come just six years after the LIGO/Virgo collaboration first detected the gravitational waves confirming predictions regarding ripples in the fabric of spacetime by Einstein’s theory of general relativity a century previous.

Though further observations are needed, the results produced by the team could help astronomers and astrophysicists refine their knowledge of systems in which these elusive mergers occur determining both how these mixed binary pairings form and how frequently their components spiral together and merge.

“Gravitational waves have allowed us to detect collisions of pairs of black holes and pairs of neutron stars, but the mixed collision of a black hole with a neutron star has been the elusive missing piece of the family picture of compact object mergers,” says Chase Kimball, a Northwestern University graduate student. “Completing this picture is crucial to constraining the host of astrophysical models of compact object formation and binary evolution. Inherent to these models are their predictions of the rates that black holes and neutron stars merge amongst themselves.

“With these detections, we finally have measurements of the merger rates across all three categories of compact binary mergers.”

Chase Kimball, Northwestern University

Kimball is the co-author of a study published in the Astrophysical Journal Letters and part of a team that includes researchers from the LIGO Scientific Collaboration (LSC), the Virgo Collaboration and the Kamioka Gravitational Wave Detector (KAGRA) project.

A Gravitational-Wave Signal Signal One Billion Years in the Making

One of the most astounding things about the detection of gravitational waves is just how precise a piece of equipment has to be to detect these tiny ripples in the fabric of spacetime. Since that first key detection in 2015, the National Science Foundation’s (NSF) operators at the LIGO laser interferometer and their counterparts at the Virgo detector in Italy have detected over 50 gravitational wave signals from mergers between black hole pairs and neutron star binaries.

The first mixed neutron star/black hole merger spotted by the collaboration on January 5th is believed to be the result of a merger of a black hole six times the mass of the Sun and a neutron star with a mass 1.5 times that of our star. The event which has been designated GW200105 occurred 900 million light-years away from Earth and was picked up as a strong signal at the LIGO detector located in Livingstone, Louisiana.

The masses of neutron stars and black holes measured through gravitational waves (blue and orange) and electromagnetic observations (yellow and purple). GW 200105 and GW 200115 are highlighted as the merger of neutron stars with black holes. (LIGO-Virgo / Frank Elavsky, Aaron Geller / Northwestern)

LIGO Livingstone’s partner detector located in Hanford, Washington, missed the signal as it was offline at the time. Virgo on the other hand caught the signal but it was somewhat obscured by noise. “Even though we see a strong signal in only one detector, we conclude that it is real and not just detector noise,” says Harald Pfeiffer, group leader in the Astrophysical and Cosmological Relativity department at Max Planck Institute for Gravitational Physics (AEI) in Potsdam, Germany. “It passes all our stringent quality checks and sticks out from all noise events we see in the third observing run.”

The fact that GW200105 was only strongly picked up by one detector makes it difficult to pinpoint in the sky with the international team only able to ascertain that it came from a region about 34 thousand times the size of the Moon.

“While the gravitational waves alone don’t reveal the structure of the lighter object, we can infer its maximum mass,” says Bhooshan Gadre, a postdoctoral researcher at the AEI. “By combining this information with theoretical predictions of expected neutron star masses in such a binary system, we conclude that a neutron star is the most likely explanation.”

Despite the fact that the second mixed merger occurred farther away–1 billion light-years distant from Earth– its signal was spotted by both LIGO detectors and the Virgo detector. This means that the team have been able to localise the merger–named GW200115– more precisely, to a region of the sky that is around three thousand times the size of Earth’s moon. This second merger is believed to have occurred between a black hole nine times the mass of our Sun and a neutron star almost twice the size of the Sun.

These Black Holes Weren’t Messy Eaters

Because of the extraordinary distances involved, astronomers have yet to confirm either merger in the electromagnetic spectrum upon which traditional astronomy is based. Despite being informed of the event almost immediately astronomers could not find telltale flashes of light indicating the mergers.

This is unsurprising as any light from such distant events would be incredibly dim after one billion years of journeying to Earth no matter what wavelength it is observed in, or how powerful the telescope is that is used to attempt the follow-up observation.

There also remains another possibility why no light could be seen from these events. The lack of a signal in electromagnetic radiation could be because the neutron star elements of these mergers were swallowed whole by their black hole partners.

“These were not events where the black holes munched on the neutron stars like the cookie monster and flung bits and pieces about,” explains Patrick Brady, a professor at the University of Wisconsin-Milwaukee and Spokesperson of the LIGO Scientific Collaboration, colourfully. “That ‘flinging about’ is what would produce light, and we don’t think that happened in these cases.”

From a MAYA collaboration numerical relativity simulation of a neutron star-black hole binary merger. Focused on the merging objects showing the disruption of the neutron star. (Deborah Ferguson (UT Austin), Bhavesh Khamesra (Georgia Tech), Karan Jani (Vanderbilt))

Whilst these are the first two confirmed examples of such mixed mergers, there have been suspects spotted by their gravitational-wave signals in the past. In August 2019 a signal designated GW190814 was detected which researchers say involved a collision of a 23-solar-mass black hole with an object of about 2.6 solar masses. This second object could have been either the heaviest known neutron star or the lightest known black hole ever found. That ambiguity left this signal unconfirmed as the product of a mixed merger event and other similar finds have been plagued with similar ambiguities.

Now that two confirmed detections of mixed mergers have been made, astrophysicists can set about discovering if current estimates that say such collisions should occur at a frequency of around one per month within a distance of 1 billion light-years of Earth are correct.

They can also set about discovering the origins of such binaries, possibly eliminating one or two of the proposed locations in which such events are believed to occur: stellar binary systems, dense stellar environments including young star clusters, and the centers of galaxies.

Key to these investigations will be the fourth observation run of the laser interferometers that act as our gravitational wave detectors, set to begin in summer 2022.

“The detector groups at LIGO, Virgo, and KAGRA are improving their detectors in preparation for the next observing run scheduled to begin in summer 2022,” concludes Brady. “With the improved sensitivity, we hope to detect merger waves up to once per day and to better measure the properties of black holes and super-dense matter that makes up neutron stars.”

Scientists peer back in time to find the birth of the first stars

Six galaxies detected by Hubble and Spitzer come from a time astronomers call the Cosmic Dawn — a period in the history of our universe just 250-350 million years after the Big Bang (the age of the universe is currently estimated at 13.8 billion years), when the first stars had just started shining.

After the Big Bang, the universe was a bit of a hot mess. It was hot, dense, and virtually opaque. It only became transparent during a period called Recombination, in which a soup of protons and electrons combined to form the first true hydrogen atoms. Prior to the Recombination, the light was not able to travel freely travel through the universe as it was constantly scattered off the free electrons and protons. But as the atoms started combining and there were fewer free particles, this forged a free path for light to travel the universe.

It is in this period that the universe became transparent — and it is also in this period that the six galaxies were formed. It took light from these galaxies most of the universe’s current lifetime to get to us, and looking at them is basically like looking at the Cosmic Dawn. For Professor Richard Ellis from University College London, UK, observations like this are the crowning of decades of work.

In a study published in Monthly Notices of the Royal Astronomical Society, Ellis and colleagues from the UK, Germany, and US, estimated the time at which the Cosmic Dawn began by using six galaxies which they estimate to have formed between 250 to 350 million years after the Big Bang.

Webb will be able to see back to when the first bright objects (stars and galaxies) were forming in the early universe. Credit: STSci.

In order to estimate the galaxies’ age, they must first consider a particular value of the universe’s rate of expansion (over which there is still some debate). The reason for that is because they are computing the lookback time — the time light from the ancient galaxies traveled to reach us.

As the universe expands, light coming from stars and galaxies has its wavelength increased — something called the redshift effect. By looking at how much the wavelength has increased, researchers can estimate how much light has traveled — and consequently, how old the light-producing object is.

The recent results were based on data from the Hubble and Spitzer space telescopes, both famous for being capable of observing some of the oldest objects in the universe. To estimate the redshift, the team required the Chilean Atacama Large Millimetre Array (ALMA), the European Very Large Telescope, the twin Keck telescopes in Hawaii, and Gemini-South telescope. 

A and B are two of the galaxies used to estimate the Cosmic Dawn in the MNRAS publication. Credits: The science team members are G. Illingworth (University of California, Santa Cruz), P. Oesch (University of California, Santa Cruz; Yale University), R. Bouwens, I. Labbé, R. Smit, and M. Franx (Leiden University), P. van Dokkum and I. Momcheva (Yale University), M. Ashby, G. Fazio, J.-S. Huang, and S. Willner (Harvard-Smithsonian Center for Astrophysics), V. Gonzalez (University of California, Riverside), D. Magee (University of California, Santa Cruz), M. Trenti (University of Cambridge), G. Brammer (STScI), R. Skelton (South African Astronomical Observatory), and L. Spitler (Macquarie University/AAO).

The age of the sample is only computed by combining data from all those different telescopes. However, astronomers and cosmologists have great expectations of the Hubble/Spitzer successor, the James Webb Space Telescope (JWST). The most ambitious, the biggest, and the most sensitive telescope NASA created will be able to observe those Cosmic Dawn galaxies directly. JWST is also the hope of a larger sample of galaxies, providing a better representation of the Cosmic Dawn.

Chaotic Young Star System Holds the Key to Planet Formation

One of the major problems which has hindered our understanding of planet formation has been the lack of direct measurements of the mass of planet-forming protoplanetary discs. Now, by successfully measuring the mass of a unique protoplanetary disc for the first time, astronomers have confirmed that gravitational instabilities play a key role in the formation of planets.

The team of astronomers, led by Teresa Paneque-Carreño, a PhD student at the University of Leiden and the European Southern Observatory (ESO), used gas velocity data collected using the Atacama Large Millimeter/submillimeter Array (ALMA) to make observations of the young star Elias 2-27 which is surrounded by a disc of gas and dust with some extraordinary features.

The star which is located just under 400 light-years from Earth in the constellation Ophiuchus has been a popular target for investigation by astronomers for at least five decades which paid off in 2016 with the discovery that the young star is surrounded by a disc of gas and dust. This marks the first time, however, that such a mass measurement has been made and gravitational instabilities have been confirmed.

Using gas velocity data, scientists observing Elias 2-27 were able to directly measure the mass of the young star’s protoplanetary disk and also trace dynamical perturbations in the star system. Visible in this paneled composite are the dust continuum 0.87mm emission data (blue), along with emissions from gases C18O (yellow) and 13CO (red). (ALMA (ESO/NAOJ/NRAO)/T. Paneque-Carreño (Universidad de Chile), B. Saxton (NRAO))

“How exactly planets form is one of the main questions in our field. However, there are some key mechanisms that we believe can accelerate the process of planet formation,” explains Paneque-Carreño. “We found direct evidence for gravitational instabilities in Elias 2-27, which is very exciting because this is the first time that we can show kinematic and multi-wavelength proof of a system being gravitationally unstable.

“Elias 2-27 is the first system that checks all of the boxes.”

Teresa Paneque-Carreño, University of Leiden

Paneque-Carreño is the first author of one of two papers detailing the team’s findings–which give astronomers the key to unlocking the mystery of planet formation– published in the latest edition of The Astrophysical Journal.

What makes Elias 2-27 the Ideal System for Cracking the Planet Formation Mystery?

Researchers have known for some time that protoplanetary discs of gas and dust surrounding young stars are locations of planet formation and we have certainly no shortage of studies of such structures. But, despite having this knowledge and a wealth of observational data, the exact process that leads to the birth of a planet has remained a puzzle.

This beautiful image, captured with ALMA shows the protoplanetary disc surrounding the young star Elias 2-27 which could be the key to solving the mystery of planet formation (B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO))

Fortunately, telltale evidence of gravitational instabilities around Elias 2-27 made it the ideal star for astronomers in order to conduct a thorough investigation of planet formation.

“We discovered in 2016 that the Elias 2-27 disk had a different structure from other already studied systems, something not observed in a protoplanetary disk before: two large-scale spiral arms,” remarks principal investigator Laura Pérez, Assistant Professor at the Universidad de Chile. “Gravitational instabilities were a strong possibility, but the origin of these structures remained a mystery and we needed further observations.”

It was Pérez who suggested that ALMA–a series of 66 radio telescopes located in the Atacama Desert of northern Chile–should be trained on the spiral of gas and dust surrounding this young star.

It was this further study that revealed, not only does Elias 2-27 possess a protoplanetary disc with signs of gravitational instabilities within it, it also has something unique for such a structure: spiral arms.

Elias 2-27: A Unique and Chaotic Young Star System

The presence of spiral arms in the protoplanetary disc is believed to be the result of perturbations caused by density waves throughout the gas and dust that comprise it.

It is the first star-forming disc discovered with such features. But, to Paneque-Carreño it signals the presence of something else within the disc, chaos. This chaotic nature also gives rise to another characteristic never seen in a disc such as this.

“There may still be new material from the surrounding molecular cloud falling onto the disc, which makes everything more chaotic,” says the graduate of the Universidad de Chile. “The Elias 2-27 star system is highly asymmetric in the gas structure. This was completely unexpected, and it is the first time we’ve observed such vertical asymmetry in a protoplanetary disc.”

Elias 2-27 is a young star located just 378 light-years from Earth. The star is host to a massive protoplanetary disk of gas and dust, one of the key elements to planet formation. In this graphic illustration, dust is distributed along a spiral-shaped morphology first discovered in Elias 2-27 in 2016. The larger dust grains are found along the spiral arms while the smaller dust grains are distributed all around the protoplanetary disk. Asymmetric inflows of gas were also detected during the study, indicating that there may still be material infalling into the disk. Scientists believe that Elias 2-27 may eventually evolve into a planetary system, with gravitational instabilities causing the formation of giant planets. Because this process takes millions of years to occur, scientists can only observe the beginning stages. (B. Saxton NRAO/AUI/NSF)

It is the double-punch of this vertical asymmetry and large-scale perturbations giving rise to a spiral structure that Cassandra Hall, Assistant Professor of Computational Astrophysics, University of Georgia, believes has major implications for our theories of planet formation.

“This could be a ‘smoking gun’ of gravitational instability, which may accelerate some of the earliest stages of planet formation,” says Hall, a co-author of one of the papers detailing these findings. “We first predicted this signature in 2020, and from a computational astrophysics point of view, it’s exciting to be right.”

This research has cracked the problem of measuring the mass of a protoplanetary disc, thus removing a significant barrier in our understanding of planet formation. This was possible in large part due to the high sensitivity of ALMA’s observing bands, particularly band 6 which covers light with a wavelength of 1.1 to 1.4 nanometres in combination with bands 3 and 7–which cover 2.6 – 3.6 nm and 0.8 -1.1 nm, respectively.

“Previous measurements of protoplanetary disc mass were indirect and based only on dust or rare isotopologues. With this new study, we are now sensitive to the entire mass of the disc,” says the second paper’s lead author Benedetta Veronesi, a postdoctoral researcher at École normale supérieure de Lyon. “This finding lays the foundation for the development of a method to measure disc mass that will allow us to break down one of the biggest and most pressing barriers in the field of planet formation. “

“Knowing the amount of mass present in planet-forming discs allows us to determine the amount of material available for the formation of planetary systems, and to better understand the process by which they form.”

Benedetta Veronesi, École normale supérieure de Lyon

More Planet Formation Mysteries to Solve

Even though this research has answered some of the questions surrounding the process of planet formation, like the best scientific discoveries, it has also given rise to new questions.

Whilst mysteries still remain surround the process of planet formation, equipped with the stunning observational power of ALMA researchers are up to the challenge (NRAO)

“While gravitational instabilities can now be confirmed to explain the spiral structures in the dust continuum surrounding the star, there is also an inner gap, or missing material in the disk, for which we do not have a clear explanation,” explains Paneque-Carreño.

Many of these questions are difficult to answer because of the vast difference between the timescales on which we live and those taken by the processes that birth planets.

“Studying how planets form is difficult because it takes millions of years to form planets. This is a very short time-scale for stars, which live thousands of millions of years, but a very long process for us,” said Paneque-Carreño. “What we can do is observe young stars, with disks of gas and dust around them, and try to explain why these disks of material look the way they do. It’s like looking at a crime scene and trying to guess what happened. “

Fortunately, researchers like Paneque-Carreño, Cassandra Hall, and Benedetta Veronesi are prepared to tackle this monumental challenge and solve planet formation’s remaining mysteries.

“Our observational analysis paired with future in-depth analysis of Elias 2-27 will allow us to characterize exactly how gravitational instabilities act in planet-forming discs and gain more insight into how planets are formed,” concludes Paneque-Carreño.

These images, taken with the SPHERE instrument on ESO’s Very Large Telescope, show the surface of the red supergiant star Betelgeuse during its unprecedented dimming, which happened in late 2019 and early 2020. The image on the far left, taken in January 2019, shows the star at its normal brightness, while the remaining images, from December 2019, January 2020 and March 2020, were all taken when the star’s brightness had noticeably dropped, especially in its southern region. The brightness returned to normal in April 2020. (ESO/M. Montargès et al)

Astronomers Solve the Mystery of Betelgeuse’s ‘Great Dimming’

In late 2019 and early 2020 Betelgeuse, a red supergiant in the constellation of Orion, made headlines when it underwent a period of extreme dimming. This dip in brightness for the star, which is usually around the tenth brightest in the night sky over Earth, was so extreme it could even be seen with the naked eye.

Some scientists even speculated that the orange-hued supergiant may be about to go supernova, an event which would have been visible in daylight over Earth for months thanks to its power and relative proximity–700 light-years from Earth. Yet, that supernova didn’t happen and Betelgeuse returned to its normal brightness.

This left the ‘great dimming’ of Betelgeuse–something never seen in 150 years of studying the star–an open mystery for astronomers to investigate.

These images, taken with the SPHERE instrument on ESO’s Very Large Telescope, show the surface of the red supergiant star Betelgeuse during its unprecedented dimming, which happened in late 2019 and early 2020. The image on the far left, taken in January 2019, shows the star at its normal brightness, while the remaining images, from December 2019, January 2020, and March 2020, were all taken when the star’s brightness had noticeably dropped, especially in its southern region. The brightness returned to normal in April 2020. (ESO/M. Montargès et al.)

Now, a team of astronomers led by Miguel Montargès, Observatoire de Paris, France, and KU Leuven, Belgium, and including Emily Cannon, KU Leuven, have found the cause of this dimming, thus finally solving this cosmic mystery. The researchers have discovered that the darkening of Betelgeuse was caused by a cloud of dust partially concealing the red supergiant.

“Our observations show that the Southern part of the star was hidden and that the whole disk of the star was fainter. The modelling is compatible with both a cool spot of the photosphere and a dusty clump in front of the star,” Montargès tells ZME Science. “Since both signatures have been detected by other observers, we conclude that the Great Dimming was caused by a cool patch of material that, due to its lower temperature, caused dust to form in gas cloud ejected by the star months to years before.”

The ‘great dimming’ of this massive star lasted a few months presented a unique opportunity for researchers to study the dimming of stars in real-time.

“The dimming of Betelgeuse was interesting to professional and amateur astronomers because not only was the appearance of the star changing in real time we could also see this change with the naked eye. Being able to resolve the surface of a star during an event like this is unprecedented.”

Emily Cannon, KU Leuven

The team’s research is published in the latest edition of the journal Nature.

A Unique Opportunity to Capture a Dimming Star

Montargès and his team first trained the Very Large Telescope (VLT)–an ESO operated telescope based in the Atacama Desert, Chile–on Betelgeuse when it began to dim in late 2019. The astronomers took advantage of the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument at the VLT as well as data from the telescope’s GRAVITY instrument. This allowed them to create stunning images tracking the great dimming event allowing them to distinguish it from regular dips in brightness demonstrated by the supergiant stars.

Betelgeuse has been seen to decrease in brightness before as a result of its convection cycle, which causes material to rise and fall throughout the star’s layers based on its temperature. This convection cycle results in a semi-regular dimming cycle that lasts around 400 days.

When the ‘great dimming’ was first observed in October 2019 astronomers had assumed this was due to its natural dimming cycle. That assumption was dismissed by December that same year when the star became the darkest that it had been in a century. The star had returned to its normal brightness by April 2020.

“No other red supergiant star has been seen dimming that way, particularly to the naked eye. Even Betelgeuse that has been closely monitored for 150 years has not shown such behaviour.”

Miguel Montargès, Observatoire de Paris, France

Not only does this finding solve the mystery of this star’s dimming, but it also provides evidence of the cooling of a star causing the creation of stardust which goes on to obscure the star.

Even though Betelgeuse is much younger than the Sun–10 million years old compared to our star’s age of 4.6 billion years–it is much closer to the supernova explosion that will signal the end of its lifecycle. Astronomers had first assumed that dimming was a sign that the red supergiant was exhibiting its death throes ahead of schedule.

Thanks to the work of Montargès and his team, we now know this isn’t the case. The dimming is the result of a veil of stardust obscuring the star’s southern region.

“We have observed dust around red supergiant stars in the past,” Cannon explains. “However, this is the first time we have witnessed the formation of dust in real-time in the line of sight of a red supergiant star,”

This stardust will go on to form the building blocks of the next generation of stars and planets, and the observations made by Montargès, Cannon and the team represent the first time we have seen an ancient supergiant star ‘burping’ this precious material into the cosmos.

The Giant that Burped Stardust

The surface of Betelgeuse–which with its diameter of around 100 times that of the Sun would consume the orbits of the inner planets including Earth were it to sit in our solar system–is subject to regular changes as bubbles of gas move around it, change in size, and swell beneath it. Montargès, Cannon and their colleagues believe that sometime before the great dimming began the red supergiant ‘burped’ out a large bubble of gas.

This bubble moved away from the star leaving a cool patch on its surface. It was within this cool patch that material was able to solidify, creating a cloud of solid stardust. The team’s observations show for the first time that stardust can rapidly form on the surface of a star.

“We have directly witnessed the formation of so-called stardust,” says Montargès. “The dust expelled from cool evolved stars, such as the ejection we’ve just witnessed, could go on to become the building blocks of terrestrial planets and life.”

One explanation for why Betelgeuse went dark in 2019 is that the star ‘burped’ out a burst of gas and dust (illustrated, left), which condensed into a dark cloud and left a cool patch of stardust on the star’s surface. (right). (NASA, ESA, E. WHEATLEY/STSCI)

With regards to the future, the researchers point to the Extremely Large Telescope (ELT), currently under construction in the Atacama Desert as the ideal instrument to conduct further observations of Betelgeuse. “With the ability to reach unparalleled spatial resolutions, the ELT will enable us to directly image Betelgeuse in remarkable detail,” says Cannon. “It will also significantly expand the sample of red supergiants for which we can resolve the surface through direct imaging, further helping us to unravel the mysteries behind the winds of these massive stars.”

For Montargès solving this mystery and observing a phenomenon for the first time, solidifies a lifetime of fascination with Betelgeuse and points towards a deeper understanding of the stardust that is the building blocks of stars, planets, and us. “We have seen the production of star dust, materials we are ourselves made of. We have even seen a star temporarily change its behavior on a human time scale.”