Artificial intelligence is allowing scientists to see the sources of gravitational wave faster and more accurately than ever before. Credit: James Josephide
Following the recent overwhelming success of deep learning and artificial intelligence in several fields of research, industry and medicine, researchers from the ARC Centre of Excellence of Gravitational Wave Discovery (OzGrav) and the University of Western Australia (UWA), including PhD student and the paper’s first author Chayan Chatterjee, have built a deep learning model using an Artificial Neural Network to pinpoint where in the sky gravitational wave signals have come from. The model can localise the source of gravitational waves produced by colliding pairs of black holes potentially as much as a thousand times faster than any other technique.
Professor Amitava Datta, a scientist from UWA who contributed to the study, says: ‘This work is a very interesting example of learning patterns from simulated data for predicting the outcome of real events, in this case the location of gravitational wave sources. Perhaps this approach using deep learning will be more and more useful in basic sciences in general.’
Data intensive astronomy expert Kevin Vinsen from the International Centre for Radio Astronomy Research says: ‘This project is an excellent example of how a multi-disciplinary approach can solve the problem’.
The basic structure of an Artificial Neural Network. The circles represent the neurons or nodes and the arrows represent connections between one neuron to another. Credit: Chayan Chatterjee
Gravitational waves are small ripples in the space-time continuum caused by colossal stellar events such as colliding black holes. In September 2015, following recent advances in detector sensitivity, the LIGO Scientific Collaboration detected gravitational waves for the first time. This was a landmark achievement in human discovery and heralded the birth of the new field of gravitational wave astronomy.
The need for speed and accuracy is particularly important in the context of gravitational wave localisation—scientists need to tell a global network of telescopes where to point on the sky as quickly as possible, so they can see any electromagnetic light that may also have come from the gravitational wave event. The current algorithm used to locate gravitational wave sources in real time takes a few seconds to process. More accurate methods usually take several hours to compute. The light generated by gravitational wave events can be very short-lived at certain wavelengths, like short gamma ray bursts, which last a mere 2-3 seconds, so scientists need methods that can rapidly process huge data as fast and accurately as possible.
The idea behind deep learning is simple: it’s an algorithm designed to mimic the functioning of neurons in our brain to carry out tasks, like categorising observed stimuli. This is done by making the network learn the correlations between a labelled input dataset and the output it is trying to predict. Just like electric signals or synapses flow through neurons in our brain, the input information provided to an Artificial Neural Network travel through layers of nodes (usually several layers deep), with each layer introducing some non-linearity to the input. This non-linearity helps the network learn complex features of the data. The ‘learning’ happens through a rigorous ‘training’ of the network. During the training, the predictions of the network are compared with the true values, and the parameters of the network are adjusted to minimise any erroneous gaps.
In their recently published paper, Chatterjee and the team from UWA successfully trained the Artificial Neural Network to learn the input data for source localisation. The data was pre-processed to extract the important physical Physics parameters from simulated gravitational wave signals, injected into ‘random noise’. The network classified these signals into several classes and accurately identified the source direction of the gravitational waves. The model localised the test samples much faster than other methods and at a low computational cost. The researchers plan to extend this work for pairs of merging neutron stars and neutron star-black hole systems.
Chatterjee says: ‘Hopefully the methods we introduce can also be translated to other areas of research and industry and help further untap the seemingly limitless potential of deep learning and artificial intelligence’.
OzGrav’s Chief Investigator Professor Linqing Wen who led the study says: ‘The future is wide open for gravitational wave discovery using the machine learning technique’.
This paper is an outcome of a multi-disciplinary collaboration of UWA’s Gravitational Wave Astronomy Group led by OzGrav’s Chief Investigator Professor Linqing Wen, data intensive astronomy expert Kevin Vinsen from International Centre for Radio Astronomy Research (ICRAR), and Professor Amitava Datta of UWA’s Computer Science and Software Engineering.
Link to publication: https://journals.aps.org/prd/abstract/10.1103/PhysRevD.100.10302
Artist's impression of the binary neutron star merger producing GW190425. Credit: National Science Foundation/LIGO/Sonoma State University/A. Simonnet.
A new collaborative study with the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) reveals a possible collision of two neutron stars earlier in 2019—only the second time this type of cosmic event had ever been detected. The gravitational-wave observatory network, that includes the National Science Foundation's LIGO and the European Virgo detectors, picked up what appeared to be gravitational ripples from a collision of two neutron stars back on 25 April 2019.
Gravitational waves and light were first witnessed in the same event in 2017. This second event in 2019, called GW190425, did not result in any light being detected; however, researchers have learned that the collision resulted in a merged object with an unusually high mass.
OzGrav postdoctoral researcher Simon Stevenson says: ‘This event is a perfect example of how gravitational-wave astronomy is a completely new and unique way of looking at the Universe. Binaries with similar masses to this event may not exist in the Milky Way or may be completely invisible to conventional radio telescopes’.
Neutron stars are the remnants of dead stars that exploded. When two neutron stars spiral together, they undergo a violent merger that sends gravitational waves shuddering through the fabric of space and time.
The gravitational waves first detected in 2015 were generated by the fierce collision of two black holes. Since then, scientists have registered dozens of new candidate black hole mergers. The first detection of a neutron star merger took place two years later, in 2017.
OzGrav Postdoctoral Researcher Vaishali Adya says: ‘This detection manifests the importance of continued improvement of the already amazingly sensitive gravitational wave detectors, as this event would not have been observable prior to the latest upgrades. OzGrav played a vital role in these upgrades, one of which involved reducing the quantum noise in the detectors’.
OzGrav Postdoctoral Researcher Xingjiang Zhu says: ‘The combined mass of the merging objects is surprisingly high, much greater than any previously known double neutron star binaries including the one detected in 2017. This provokes us to think about the nature of this event and how the source might have been formed’.
The combined mass of the merged bodies in this event is about 3.4 times that of the mass of the Sun. Typically, neutron star collisions are only known to happen between pairs of neutrons stars with a total mass up to 2.9 times that of the Sun. One possibility for the unusually high mass is that the collision took place not between two neutron stars, but a neutron star and a black hole, since black holes are heavier than neutron stars. But if this were the case, the black hole would have to be exceptionally small for its class. Instead, the scientists believe it is more likely that the event was a shattering of two neutron stars and that their merger resulted in a newly formed black hole.
Neutron star pairs are thought to form either early in life—when companion massive stars successively die one by one—or when they come together later in life within dense, busy environments. The data from the 2019 event do not indicate which of these scenarios is more likely—more data and new models are needed to explain the unexpectedly high mass. The discovery suggests that we may have detected an entirely new population of binary neutron star systems.
OzGrav Associate Investigator Greg Ashton says: ‘This event was really interesting. The chirp-like signal was seen by two of the three detectors for about 128 seconds before the final merger. Unfortunately, one of the detectors was not observing at the time, which meant that the sky localization was poor. Perhaps because of this, and because it was so far away, no electromagnetic light was observed from this event. Nevertheless, we saw it very clearly in the gravitational wave data and could use that to calculate the masses, spins, and orientations of the objects’.
‘Additional exciting and unexpected discoveries can be expected as the sensitivity of the LIGO detectors improves. OzGrav is working closely with LIGO to improve their sensitivity, developing new instrumentation and analysis techniques’, says Professor Peter Veitch, University of Adelaide OzGrav Node Leader
The results were announced today at the American Astronomical Society meeting in Honolulu, Hawaii.
The full scientific article will be available here post-embargo: https://dcc.ligo.org/P190425/public
AS FEATURED IN THE AGE
Local scientists have begun the groundwork for a campaign to potentially make Australia the site of one of the biggest science instruments ever built.
Nicknamed Cosmic Explorer South, the 40-kilometre long, $1.5 billion instrument is designed to detect ripples in space time throughout the entire universe.
The global astronomy community is drawing up plans for three such detectors based around the world, which are slated for construction in the 2030s.
Australia is the perfect place to build one, local scientists believe.
"There is no doubt in my mind that Australia is the best location for this," says Professor Matthew Bailes, who directs the Australian Research Council Centre of Excellence for Gravitational Wave Discovery and is spearheading Australia’s bid, along with Professor David McClelland at the Australian National University.
"We don’t have a preferred site yet. But we have been placing little L-shaped things on maps to see where they might fit."
Explorer South is a next-generation gravitational wave detector. It would be able to sense gravitational waves from the very first stars born in the universe.
It will consist of two, 40-kilometre long vacuum tubes placed at right angles, like a big L.
Down the middle scientists would fire a "James Bond-strength" laser, says Professor Bailes.
A device of that size would dwarf another piece of big science, the Large Hadron Collider, which is 27 kilometres in diameter and straddles the Franco-Swiss border.
A white paper for the gravitational wave project was quietly submitted to the Australian Academy of Science earlier this year, proposing an initial $5 million investment to begin exploratory work.
The technique has already been proved by the American-based LIGO, which first detected a gravitational wave in 2015, using two arms, each four kilometres long.
How it works
When black holes collide, so much energy is released it causes ripples in space time.
These ripples spread out through the universe, like ripples on a pond. When they reach Earth, they slightly stretch and then shrink our space-time (yes, you are being very slightly stretched and shrunk too). As a gravitational wave passes through Earth, LIGO's arms stretch a little; a laser beam shone down the middle of the arms allows scientists to detect that tiny change in distance.
Scientists now want to go further – using those ripples to get information about the formation of the universe. To do that, they need to go bigger.
International astronomers are now planning the next generation of gravitational wave detectors. One wave detector, the Einstein Telescope, is planned in Europe. Another, Cosmic Explorer, is being planned for America.
A third detector in the southern hemisphere – Cosmic Explorer South – would allow scientists to triangulate the source of any waves they detected. Senior experts from the National Science Foundation, the American government’s science funding agency, are aware of Australia's interest.
Any location needs to be extremely flat and geologically stable, which makes Australia’s vast interior perfect. The arms of the detector need to be perfectly straight. But if you build something 40 kilometres long, you need to take into account the Earth’s curve.
"So you want to find a valley, where the shape of the valley is exactly compensated by the curve of the Earth," says Professor Bailes.
If you were to place it in Melbourne’s CBD, one 40 kilometre arm would stretch nearly to Healesville and the other well past Sunbury. The extreme size makes Cosmic Explorer South 100 times more powerful than LIGO, says Professor Bailes. It could measure distances down to one ten-thousandth of the width of a proton, and be sensitive enough to detect the gravity of a passing cloud.
Professor Bailes would not reveal any possible locations, because of the risk of land speculators buying them. But it would need to be near an airport or regional hub, he said. The government needs long lead times on science mega-projects, and there is a lot of due diligence to do before asking for government funding, Professor Bailes says.
If Explorer South were built here, Australia would likely have to spend about $300 million on the project, with the rest kicked in by governments around the world.
AS FEATURED IN THE AGE.
Neutron stars are among the densest objects in the Universe, and they rotate extremely fast and regularly.
Until they don’t.
Occasionally, these neutron stars start to spin even faster, caused by portions of the inside of the star moving outwards. It’s called a ’glitch’, and it’s a rare glimpse into what lies within these mysterious objects.
In a recent paper published in Nature Astronomy, a team from the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) at Monash University; McGill University, in Canada; and the University of Tasmania, studied the Vela Pulsar: a neutron star in the southern sky, 1,000 light years away from Earth.
According to the paper’s first author Dr Greg Ashton, from OzGrav-Monash, only 5% of pulsars are known to glitch and Vela ‘glitches’ about once every three years. This makes Vela a famous prized jewel among ‘glitch hunters’ like Ashton and his colleague, Dr Paul Lasky, also from OzGrav-Monash.
By reanalysing data from observations of the Vela glitch in 2016, taken by co-author Jim Palfreyman from the University of Tasmania, Ashton and his team found that during the glitch the star started spinning even faster, before relaxing down to a final state.
According to Dr Lasky, this observation (done at the Mount Pleasant Observatory in Tasmania) is particularly important because, for the first time, scientists got invaluable insights into the interior of the star, revealing that the inside of the star actually has three different components.
“One of these components, a soup of superfluid neutrons in the core, moves outwards first and hits the rigid crust of the star causing it to spin up. But then, a second soup of superfluid that moves in the crust catches up to the first causing the spin of the star to slow back down. This overshoot has been predicted a couple of times in the literature, but this is the first real time it’s been identified in observations,” he said.
One such prediction of the overshoot came from the study’s co-author Vanessa Graber, from McGill University, who visited the Monash team as an OzGrav international visitor earlier this year.
Another observation, according to Dr Ashton, defies explanation: “Immediately before the glitch, we noticed that the star seems to slow down its rotation rate before spinning back up. We actually have no idea why this is, and it’s the first time it’s ever been seen! We speculate it’s related to the cause of the glitch, but we’re honestly not sure,” he said. Ashton suspects this paper will spur some new theories on neutron stars and glitches
OzGrav Associate Investigator Adam Deller and the Distributed FX Correlator (DiFX) team was recently awarded the Peter McGregor Prize by the Astronomical Society of Australia (ASA). This is a newly created and prestigious award to celebrate major achievements in the development of astronomical instrumentation and technology, both hardware and software.
The Distributed FX Correlator (DiFX) is a software package that contains tools necessary to turn an array of radio telescope signals into a functioning radio interferometer. The nominations and letters of support made a very strong case arguing the innovative nature of the DiFX and its impact.
The DiFX transformed long-baseline interferometry. It has contributed significantly to reducing the barrier to entry and play a major role in radio astronomy research internationally. The system has enabled a wide range of science, as testified by the very high number of references to the key technical papers. The open-access nature of the software has put a new tool in the hands of astronomers, with demonstrated positive results. Its scalability and adaptability continues to enable researchers to tailor its behaviour and pursue what would otherwise be difficult science goals. DiFX was also used to image the black hole event horizon in 2018, so it’s evidently powerful.
The DiFX collaboration includes the following contributors:
Adam Deller (leader), Walter Alef, James Anderson, Matthias Bark, Matthew Bailes, Walter Brisken, Roger Cappallo, Geoff Crew, Richard Dodson, Dave Gordon, Zheng Meyer-Zhao, John Morgan, Chris Phillips, Cormac Reynolds, Jon Romney, Helge Rottman, John Spitzak, Matteo Stagni, Steven Tingay, Jan Wagner, Mark Wainright, Randall Wayth."
Congratulations to everyone involved!
Image by James Josephides.
The Hubble constant is one of the most fundamental pieces of information that describes the state of the Universe in the past, present, and future. It tells us how fast the Universe is expanding – a valuable piece of information in science’s search for answers.
The two best ways of estimating the Hubble constant are based on: the background hiss of the Universe left over from the big bang (the ‘Planck’ observations of the cosmic microwave background radiation), and on massive stars blowing themselves to pieces in the distant Universe (‘type 1a supernovae’ observations). According to the measurements of the exploding stars, the Universe is expanding a bit faster than the measurements of the background hiss would indicate, and the difference is now very significant. So, either one of them is incorrect or something is missing in our understanding of physics and cosmology. We’d like to know what is really happening in the Universe, so we need a third, independent check.
This is where the merger of two neutron stars can shed some light. Neutron star mergers are phenomenally energetic events – two stars, each more massive than the Earth’s Sun, whip around each other hundreds of times per second before colliding and producing an enormous blast of material, light and gravitational waves. In 2017, gravitational waves and light were first detected from a neutron star merger that had occurred 130 million years ago, in an event scientists refer to as GW170817.
Scientists realised that a burst of gravitational waves can be used as a ‘standard siren’: based on the shape of the gravitational wave signal, we can tell how ‘bright’ the event should have been in gravitational waves. We can then measure the actual brightness of the event and work out what the distance must have been. However, this only works well if we know how the merging stars were oriented on the sky (edge on, face on, or somewhere in between).
The gravitational wave data itself can’t accurately tell whether a merger was nearby and edge on, or distant and face on. To answer that question, a team including OzGrav Associate Investigator Adam Deller used radio telescopes to take a super-high-resolution movie of a narrow but powerful jet of material left behind after two neutron stars merged in the GW170817 event. The resolution of the radio images was so high, if it was an optical camera, it would see individual hairs on someone’s head 10 km away. By examining the miniscule changes in this radio-emitting bullet of gas (compared against models developed by supercomputers), the angle of the jet and the orientation of the merging neutron stars was found.
Using this information, Adam and the team could tell how far away the merging neutron stars were and, by comparing this with how fast their host galaxy is rushing away from the Earth, they could finally work out the prized Hubble constant. Despite this incredible result, which is published in Nature Astronomy today, the current measurement is still not good enough to distinguish between ‘Planck’ vs ‘Type 1a supernovae’. Further observations of merging neutron stars will soon lead to a more accurate Hubble constant.
Image by Carl Knox.
Inside a small room in the Melbourne suburb of Hawthorn a team of astrophysicists, with a little help from work experience students and a 12-year-old boy, are leading a global hunt for one of the universe’s most mysterious and powerful phenomena.
For one week this is the control centre for about 64 telescopes dotted around – and above – the Earth.
The team is on the world’s biggest chase for fast radio bursts, mysterious and super-powerful blasts of radio-wave energy visible clear across the universe. But the Deeper Wider Faster team, as it is known, has even bigger ambitions.
Over the past few years, astronomers have spotted a number of these bursts. The CSIRO announced on Friday that it had spotted one and traced its location to a galaxy 3.6 billion light years away.
But the scientists in the Hawthorn room not only want to spot one; they hope to find out what causes the bursts.
Fast radio bursts – astronomers refer to them as FRBs – are extremely short and powerful bursts of radio waves originating from somewhere outside the Milky Way. Some contain more energy within a moment than our sun produces in decades.
“It’s a millisecond burst that goes off once, unpredictably. And you have no idea when. Trying to catch that, it’s hard,” says Jeff Cooke, chief investigator at the ARC Centre for Excellence in Gravitational Wave Discovery. He has spent the past half-decade pulling all this together.
Last week's telescope global hook-up finished on Saturday. The team hasn't spotted anything thus far, but there were problems with one of the radio telescopes and data analysis will continue to see if anything was missed.
No one knows what the bursts are. Most scientists agree they are not linked to aliens.
Each astrophysicist in the control room last week at Swinburne University’s Hawthorn campus has their own favourite theory.
Professor Cooke hopes they come from magnetars, a kind of neutron star with a super-powerful magnetic field. An incredibly intense "star-quake" on its surface might produce an FRB.
Sara Webb hopes the answer is a blitzar, a pulsar that explodes then collapses into a black hole.
And Igor Andreoni hopes FRBs come from colliding neutron stars, which generate explosions so powerful they warp the space-time fabric.
To find out, the three have spent five years wrangling telescopes around the world to work together.
The global coalition ranged from the high-tech – like IceCube, a sensor embedded deep under the Antarctic ice, and the Hard X-ray Modulation Telescope, flying in a low orbit of Earth – to decidedly low-tech: a telescope set up in a Pakenham backyard by an amateur astronomer.
The telescopes have been looking at the same patch of sky. But – and here’s the trick – they all look with different eyes. The X-ray Modulation Telescope, for example, sees in X-rays, while IceCube’s one-kilometre-wide sensor is designed to pick up neutrino signatures.
Different signals can travel through space at different speeds. Radio waves typically are the slowest. This means by the time a radio telescope detects a fast radio burst, all the other signals – things that could tell us what the FRB actually is – may have already gone racing past the Earth.
The hope for last week's hook-up was that by looking with about 64 sets of different eyes, when an FRB fired off the other telescopes would spot something – a burst of light, or X-rays, or anything at all– that gave a clue as to what the FRB really is.
The researchers have done six runs at this in the past four years, each time harnessing more and more telescopes. So far, nothing.
Data flowed last week from the telescopes around the world to a supercomputer able to pick out anything that could possibly be a signal – like a space explosion – that could generate an FRB.
The probabilities told the scientists their radio telescopes would spot one or two FRBs last week. The supercomputer, however, could identify tens of thousands of possible signals every day.
The aim was for humans to check any signals within minutes of their happening in order to send a quick command to giant telescopes in Chile and South Africa that stood ready to try to get a good image of the FRB.
However, the team will now need to go back over some of the results due to problems with a telescope not providing needed data.
Many scientists don’t even believe an FRB will come with another signal. “So that makes it even harder,” Dr Andreoni says.
In the control room one day early last week, in charge of assessing the thousands of possible FRBs is that crack team of astrophysicists – and a few work experience students. There are six of the latter, all here for the day from school. They are joined by Blake Iscaro, a 12-year-old with a deep interest in space who matter-of-factly says he is using scavenged parts to build a radio-telescope in his backyard.
The supercomputer sprays the data up on the wall. Then it's up to the team to spot something. Fast.
“Computers find things you know pretty well. They don’t find things you have not ever seen before,” Professor Cooke says. “If you’re going to trigger these gigantic telescopes, which cost a ridiculous amount of money, you don’t want them to point at something that wasn’t real.”
Two stations down from Professor Cooke, year 10 student Max Petschack leans closer to his screen, face screwed up in concentration, staring at what looks like a yellow blob.
The light curve shows the blob became dramatically brighter between measurements. “This one’s interesting,” he says.
Michelle Ko leans over to look. “Wow,” she says.
Max points at the light curve. “That’s a, what, point four difference?”
“Yeah, that’s a huge difference,” says Michelle, before calling Dr Andreoni over. He leans over the children’s shoulders, checking their work.
Is this the moment?
Sadly, he does not think so. There is a lot of turbulence in the atmosphere messing with their brightness measurements. And the dot Max found is too round. “That means it’s probably a star,” Dr Andreoni says.
By Liam Mannix - As featured in The Age.
The Laser Interferometer Gravitational-Wave Observatories (LIGO) are the world's largest gravitational wave observatories and a marvel of precision engineering. First predicted by Albert Einstein a century ago, gravitational waves are ripples in space-time. LIGO was responsible for the first direct detection of gravitational waves in 2015 and this led to the 2017 Nobel Prize in Physics being award to the three of the co-founders of the LIGO experiment.
The LIGO detectors consist of two interferometers spaced 3,000 kilometres apart in the US. Each L-shaped facility has two four-km arms positioned at right angles to the central building. Lasers traverse along each arm and bounce back from mirrors and, by exploiting the wave nature of light, these ripples in space-time can be detected. The sensitivity of these devices is such that scientists can measure a change in length as small as 1/10,000 the width of a proton, representing the incredibly small scale of the effects imparted by passing gravitational waves. Essentially, LIGO can be thought of as "ears" listening for gravitational waves, or even as a skin trying to "feel" the slightest of movements.
Students from the ARC Centre of Excellence for Gravitational Waver Discovery (OzGrav) in Adelaide, have developed a “mini LIGO” dubbed AMIGO (Adelaide’s Mini Interferometer for Gravitational-wave Outreach) through the generous support in part by OzGrav and the University of Adelaide. They use AMIGO to demonstrate the properties of light and principals of precision measurement to students of all ages. Craig Ingram, a post-graduate student at the University of Adelaide said of the students “Many would normally run a mile if you tell them that you were going to talk to them about physics. Instead [with AMIGO] we end up with the students wide-eyed and engaged.”
In the 12 months since the outreach program started in Adelaide, the researchers have delivered the program to thousands of students across the country. This includes a highly successful exhibition at the World Science Festival in Brisbane. During this two-day event, Ms Deeksha Beniwal and Ms Georgia Bolingbroke, two integral members of the AMIGO outreach team, interacted with over a thousand members of the general public.
In January this year, Mr Ingram was invited to Google X headquarters in California, home to the developers of technologies such as Google Glass and WAYMO driverless cars, to use AMIGO as a tool to explain the fundamental properties of light. According to Mr. Ingram, it is only after understanding the fundamental nature of light that we can build on this to develop new technologies that Google X are investigating, such as quantum computing.
The AMIGO interferometer consists of an eye-safe laser which is split and bounced through the use of strategically placed mirrors and laser beams. The desktop AMIGO is used to illustrate, along with the use of less technical props like ropes, to illustrate the wave nature of light and “in turn what gravitational waves are and how they are detected,” Ms Beniwal said.
“It’s a really cool way to show how the fundamentals of physics can be used to teach us about how the universe works.”
As featured on The Advertiser.
Australian scientists on the hunt for gravitational waves rely on AARNet for transferring data from LIGO detectors in the USA to OzGrav nodes in Australia for analysis.
Dozens of researchers from the Australian Research Council Centre of Excellence for Gravitational Wave Discovery (OzGrav) are part of an international team of scientists making significant discoveries in the emerging field of gravitational-wave astronomy.
Gravitational waves carry unique information about their dramatic origins and the nature of gravity. In 2015, scientists detected gravitational waves for the first time and concluded they were produced during the final moments of the merger of two black holes to produce a single, more massive spinning black hole. This collision of two black holes confirmed the predictions of Albert Einstein’s 1915 general theory of relativity.
In 2018, the scientists detected the most massive binary black hole merger yet witnessed in the universe. The black hole that resulted from this cataclysmic event is more than 80 times as massive as our Sun. The discovery – along with evidence of nine other black hole mergers – came just over one year since scientists announced they had witnessed, for the first time, the violent death spiral of two dense neutron stars via gravitational waves.
Scientists use the extremely sensitive detectors LIGO (two interferometers in the states of Louisiana and Washington, USA) and VIRGO (an interferometer in Cascina, Italy) to survey space for gravitational waves arriving at the earth from a cataclysmic event in the distant universe. Both these detectors have recently been upgraded and have almost doubled their sensitivity which means that they can survey an even larger volume of space for powerful, wave-making events, such as the collisions of black holes.
One of the key upgrades to the LIGO detectors employs a technique called “squeezing” to reduce levels of quantum noise that can mask faint gravitational-wave signals. The technique was developed at the Australian National University, and has been routinely used since 2010 at the GEO600 detector.
In April 2019, not long after the LIGO and VIRGO detectors were upgraded, there was much excitement around the world when astronomers revealed the first ever images of a black hole, created in the United States by Massachusetts Institute of Technology’s Dr Katie Bouman using enormous volumes of telescope data.
Detection data streams are analysed using high performance computing at the LIGO and VIRGO nodes. Some of this data is transferred to international collaborators over research and education networks for further analysis and discovery, including over AARNet to the OzGrav nodes at partner institutions in Australia.
OzGrav is hosted at Swinburne University in partnership with the Australian National University, Monash University, University of Adelaide, University of Melbourne, University of Western Australia, CSIRO and the Australian Astronomical Observatory and collaborators in Europe and the USA.
Colm Talbot, an OzGrav scientist from Monash University says gravitational wave astronomy requires a global approach.
“By studying black hole collisions and other wave-making events we act as cosmos archaeologists to understand how the universe works. From detecting events through to analysis and discovery, working together nationally and globally improves the quality of individual tasks and leads to better research outcomes.” he said.
AARNet provides the reliable, scalable and secure high-speed network required for moving data between OzGrav scientists and their international collaborators to support gravitational wave research.
Author: Jane Gifford from AARNet as featured on The Field.
Ripples of excitement spread through the world of science this week as astronomers revealed the first ever images of a black hole, created using reams of telescope data by MIT's Dr Katie Bouman.
Black holes must rate as one of our Universe's most mysterious phenomena - colossal, monstrous objects that devour any matter and light that dares get too close.
The images show "light swirling around the event horizon of a black hole right before falling into it, never to be seen again", UWA's Teresa Slaven-Blair told the AusSMC. "It’s this evidence of light being removed from the Universe that is so amazing."
Monash University's Professor Ilya Mandel says that this particular black hole is in Messier 87, a galaxy in the nearby Virgo cluster, and that it weighs "a whopping 6 billion times the mass of the Sun". It lives "more than 50 million light years away", he added.
So, how do you snap something in a galaxy far, far away?
Swinburne University's Dr Adam Deller says the team behind the image used radio telescopes thousands of kilometres apart and lined up their signals with extraordinary precision, "to around a millionth of a millionth of a second".
That allowed them "to make phenomenally sharp images – if your digital camera was this good, you could take a photo of a person hundreds of kilometres away and make out individual strands of hair on their head," he said. "They used this capability to capture the shadow that a supermassive black hole casts – it’s the first time astronomers have ever really 'seen' a black hole."
Curtin University's Professor Steven Tingay explained the significance of the images - confirmation of Einstein's theory of General Relativity:
"For decades, we have been studying black holes but could only indirectly see the effects of their extreme masses and gravitational fields," he said. "The images show, for the first time, the point close to the black hole from which nothing can escape, even light - the so-called event horizon...confirming the predictions of General Relativity."
"Einstein’s theory passes yet another test," confirmed OzGrav's Dr Daniel Reardon.
"It's a monster, but a very law-abiding one, precisely following the rules laid out by General Relativity," said Professor Mandel.
Read Professor Alister Graham's article in The Conversation: Observing the invisible: the long journey to the first image of a black hole.