Category: News

Celebrating the 50th anniversary of the Australia–Japan Basic Treaty of Friendship and Cooperation through science, cultural exchange and collaboration.

Young gravitational-wave researchers from Australia and Japan came together in Kanazawa to exchange scientific ideas, experience each other’s cultures and build the relationships that will shape the future of international science.

As Australia and Japan celebrate the 50th anniversary of the Basic Treaty of Friendship and Cooperation, a new generation of scientists is helping carry that relationship forward.

Signed in Tokyo in 1976, the Treaty established a foundation for enduring friendship, mutual understanding and cooperation between the two countries. Fifty years later, those principles continue to be reflected in the research partnerships, cultural exchange and people-to-people connections linking Australia and Japan.

Last week, early career researchers in gravitational-wave science and astrophysics from universities and research institutions across Australia and Japan gathered in Kanazawa for the Joint OzGrav–KAGRA Early Career Researcher School. The group included researchers connected with Australia’s ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav), the KAGRA collaboration, the Institute of Science Tokyo, the University of Tokyo and other institutions across both countries.

The school brought together cutting-edge gravitational-wave science, professional development and cultural exchange, giving emerging researchers from both countries the opportunity to learn from one another and form relationships early in their careers.

Gravitational-wave science is international by nature. Detecting tiny ripples in spacetime requires observatories, researchers and institutions around the world to work together. The school helped participants see that collaboration not only as a scientific necessity, but as something built through trust, communication and shared experience.

A major highlight was the visit to KAGRA, the world’s first underground gravitational-wave detector and the first to use cryogenically cooled mirrors.

For many of the Australian participants, travelling into the mountains of Gifu Prefecture and entering KAGRA’s kilometre-scale underground tunnels brought the science they study to life. They saw the extraordinary engineering required to detect movements far smaller than the width of an atom and met the scientists and engineers working directly on the observatory.

Across the four-day program, participants explored gravitational-wave theory, astronomy, detector instrumentation, data analysis, cosmology and fundamental physics through lectures, panels, workshops and poster presentations.

But we wanted the school to be more than a technical conference.

Scientific careers are also shaped by the ability to communicate ideas, work across disciplines and cultures, and keep going when research does not unfold as planned. Workshops explored storytelling, improvisation and scientific presentations, while a candid session on research failures encouraged participants to share experiences of rejected papers, unsuccessful experiments, coding problems and the uncertainty behind scientific progress.

There was something powerful about seeing young researchers realise they were not alone in those experiences.

Connecting through culture

The cultural exchange became one of the most memorable parts of the school.

Participants brought a small object, photograph or story representing something meaningful from their culture. In mixed Australian and Japanese groups, they shared stories about family, food, language, celebrations, landscapes and traditions.

The change in the room was immediate. People who had only just met began speaking openly, laughing together and finding connections beyond their research titles and institutions.

That spirit continued through an origami activity linking Japanese paper art with gravitational-wave science, as well as a team challenge through Kanazawa’s Omicho Market. Receptions, shared meals and informal conversations around the city gave those new connections room to grow.

These activities were not separate from the scientific purpose of the school. They were central to it.

International science depends on curiosity, trust and a willingness to understand the people behind the work. By learning about each other’s cultures and experiences, participants created a stronger foundation for future collaboration.

For me, one of the most rewarding parts of the week was watching the room change. Researchers who arrived as members of separate Australian and Japanese groups gradually became one community—sharing ideas, helping one another, celebrating each other’s work and forming friendships that I hope will continue for many years.

The school demonstrated that the future of the Australia–Japan relationship will be shaped not only by scientific excellence, but by the people behind the science. Participants returned to their institutions with new knowledge, a deeper appreciation of each other’s cultures and the beginnings of collaborations that may continue for decades.

Fifty years after Australia and Japan formalised their friendship, the next generation is already helping write its next chapter—one conversation, one collaboration and one discovery at a time.

Acknowledgements

This school would not have been possible without the dedication, generosity and countless hours contributed by our organising committee. On behalf of everyone involved, thank you for your passion, collaboration and commitment to creating an unforgettable experience for the next generation of Australian and Japanese researchers.

Japan organising team: Kentaro Somiya, Haoyu Wang, Kenta Tanaka, Hayato Imafuku, Daiki Watarai and Kazuya Kobayashi.

Australia organising team: Diana Haikal, Jackie Bondell, Neil Lu, Christine Lee, Samuel Sentschuk, Ari Hernandez and Olivia Vidal Velázquez.

Photo Gallery: A selection of moments from the Joint OzGrav–KAGRA Early Career Researcher School, capturing four days of scientific discovery, cultural exchange and the friendships that reflect the enduring partnership between Australia and Japan.

For a decade, gravitational-wave observatories have been detecting collisions between black holes across the Universe. Now, after analysing more than 150 binary black hole mergers, researchers have found evidence that these collisions can be divided into at least three distinct families, each with different characteristics and potentially different origins. 

The study, led by postdoctoral fellow Dr Sharan Banagiri from the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) and Monash University, analysed the growing catalogue of gravitational-wave detections from the international LIGO–Virgo–KAGRA (LVK) Collaboration. Researchers found that black holes appear to cluster into three subpopulations, separated by distinct mass ranges and characterised by different spin and pairing behaviours. 

The findings, published in Physical Review Letters, suggest that the Universe may not produce merging black holes through a single dominant process, as many researchers once expected. 

“The population of binary black holes that we are discovering is complex enough that we cannot easily say it looks like one formation channel is making the vast majority of black holes,” Dr Banagiri said. 

Black holes can form in a variety of environments. Some might originate from pairs of massive stars born together that eventually collapse into black holes and merge. Others may form in dense stellar clusters where black holes dynamically capture one another, while some may grow through repeated mergers over time. 

The challenge for astronomers is that they cannot directly observe how individual black holes formed. Instead, they must work backwards from the mergers they detect through gravitational waves. 

Dr Banagiri compares the problem to finding a pile of leaves on the ground and trying to work out the different kinds of trees they came from without looking at the trees themselves. 

“You can look at the leaves and say maybe that’s a maple, maybe that’s a cherry tree. By the shape and geometry of the leaves, you can roughly say there are four kinds of trees contributing to this pile of leaves.” 

What researchers do is very similar. By analysing a large catalogue of black hole mergers, they can identify patterns in the data and group black holes with similar characteristics into distinct subpopulations. 

The researchers found that two key properties proved particularly useful: how fast black holes spin and how they pair with one another. 

Based on these characteristics, the analysis revealed three distinct subpopulations of merging black holes, separated by mass: one below about 28 times the mass of the Sun, a second between roughly 28 and 40 solar masses, and a third above 40 solar masses. 

The most massive black holes appear to spin faster and pair differently from their lower-mass counterparts. 

“Smaller black holes in binaries are relatively slower spinning, and they like to pair with other black holes that are roughly the same mass,” said Dr Banagiri. 

“Black holes that are already high mass, greater than 40 solar masses, spin faster and they like to pair with something that’s less massive.” 

One possible explanation is that some of the most massive black holes are themselves the products of earlier black hole mergers. In this scenario, known as hierarchical merging, a black hole formed in a previous merger later merges again, creating progressively larger black holes. 

While the new results are consistent with that picture, the researchers stress that more observations will be needed before any individual formation pathway can be confirmed. 

“The main discovery is that you can statistically separate the detections into different clusters,” said Dr Banagiri. 

“There are very interesting clues that are starting to become visible, but that link is not yet fully clear.” 

The work highlights how gravitational-wave astronomy is entering a new phase. Rather than simply detecting black holes, researchers are beginning to study their demographics and evolutionary histories. 

The findings do not change scientists’ understanding that black holes form when massive stars collapse. Instead, they provide new clues about what shapes the characteristics of black holes throughout their evolution.  

“The question is: what kinds of environments and what kinds of physics are dictating the properties of the black holes that we see?” said Dr Banagiri. 

As gravitational-wave detectors continue to improve and future observing runs deliver hundreds or even thousands more detections, researchers hope to refine the emerging picture of how black holes form and evolve across the Universe. 

APS Physics Magazine article: Evidence Mounts for Hierarchical Black Hole Mergers

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Paper: 

Evidence for Three Subpopulations of Merging Binary Black Holes at Different Primary Masses

https://arxiv.org/abs/2509.15646

Authors: 

Sharan Banagiri, Eric Thrane and Paul D. Lasky 

Institutions: 

The ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) and Monash University 

Researchers closely observing the fiery aftermath of an immense cosmic collision have made a new measurement of the speed at which the Universe is expanding.

The international team led by researchers from the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) at Swinburne University of Technology and CSIRO, Australia’s national science agency, combined telescope and gravitational wave data in an attempt to unlock the true value of the Universe’s expansion, called the Hubble Constant.

Knowing how fast the Universe is expanding is extremely important, as it helps scientists to determine how large or far away objects are, the role of dark matter in the evolution of the Universe, as well as the Universe’s origin and ultimate fate.

Two existing measurements of the Hubble Constant have split cosmologists for more than a decade.

Lead researcher, OzGrav Partner Investigator and CSIRO’s Dr Kelly Gourdji, said the two independent measurements are described as the ‘Hubble tension’.

“One method uses data from the very early Universe -the cosmic microwave background radiation – to make the measurement, while the other uses measurements from relatively nearby supernovae, making it data from the late Universe,” Dr Gourdji said.

These precise measurements disagree with one another: either one measurement is wrong, or our understanding of the physics that govern the Universe is wrong, leaving the true nature of the Hubble Constant shrouded in mystery.

“Our independent measurement using gravitational waves is a late Universe method, but the result is more consistent with the early Universe value,” Dr Gourdji said.

The dramatic collision of two neutron stars, which was visible to telescopes and caused a gravitational wave to be detected on Earth, provided an opportunity for the team to take this new measurement.

After black holes, neutron stars are the densest objects in the Universe with a huge amount of mass in a very small area. This density creates an intense gravitational field, more than 100 billion times stronger than the gravitational field on Earth.

The collision between these neutron stars was so powerful that it sent ripples through space and time – gravitational waves – whilst also sending jets of energetic particles into space.

Professor Adam Deller, OzGrav Chief Investigator from Swinburne University of Technology, who led the radio observations used in the research, said the jets caused by the collision were essential to making the measurement.

“These jets are launched for only a couple of seconds, but as they slam into the surrounding gas, they glow for months afterwards. We analysed almost a year of observations from the Hubble Space Telescope and two different arrays of radio telescopes spread across the USA and Europe,” Professor Deller said.

By combining all the data, the team revealed a new value for the Hubble Constant which, while not as precise as the more established measurements that underpin the Hubble tension, is more accurate than previous attempts made using gravitational waves. This is the strongest indication yet that gravitational waves could settle the debate.

Professor Deller said that the finding was significant.

“Some astronomers had proposed ways in which both measurements could be correct if our understanding of cosmology was changed – but our measurement argues quite strongly against that solution,” explained Professor Deller.

Dr Gourdji said more observations would be needed to confirm the finding.

“This would suggest that there is not something wrong with our understanding of cosmology, though we’ll need to examine more neutron star mergers like this one to be sure. For now, this result adds another data-point for cosmologists to consider in the lively Hubble tension debate,” said Dr Gourdji.

Published in The Astrophysical Journal

If, in space, no one can hear you scream – it seems that you can actually hear the sound of a crash when two black holes collide.  

Using the loudest gravitational wave ever heard, two Australian scientists and colleagues have been the first to witness the previously elusive “event horizon” – at the actual moment of collision, right before all light and sound are swallowed by the newly formed black hole for eternity.  

The discovery and the novel way to analyze the data, published today in Nature, provide a new observational window onto the region closest to a black hole’s event horizon where quantum physics and theories of general relativity intersect. 

The study, led by Dr Ling (Lilli) Sun and PhD candidate, Mr Neil Lu, from the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) and the Australian National University, as well as colleagues in Canada, the US, and Spain, opens the doors for astrophysicists globally being able to observe the previously elusive event horizon of a black hole.  

“We measured the last sound the black holes made when they crashed. Hidden within that signal is a small component, called direct waves, that had not previously been well understood,” said Mr Lu. “Our new analysis allows us to decipher this component and extract unique information from close to the event horizon.” 

The event horizon is the boundary around a black hole beyond which nothing can escape, not even light. At this boundary, the speed required to break free from the black hole’s gravity equals the speed of light. Since nothing in the universe travels faster than light, anything that crosses the event horizon is permanently trapped. 

The scientists studied the gravitational-wave signal GW250114, recorded last year, the loudest yet, using the two Laser Interferometer Gravitational Wave Observatories in the United States. 

According to Dr Sun, black holes are extreme objects that sit at the intersection of general relativity and quantum theory.  

“We studied GW250114, the loudest binary black hole signal observed to date, about three times louder than the first gravitational-wave signal detected a decade ago,” said Dr Sun. “Our analysis shows that this exceptionally loud signal can be used as a powerful probe of the remnant black hole’s horizon, allowing us to measure its two fundamental properties: rotation frequency and surface gravity.” 

“These measurements mark a first step towards future tests of general relativity with direct waves,” Mr Lu added. 

The new analytical technique developed by Mr Lu, Dr Sun, and their collaborators means that astrophysicists will be able to study the strength of extreme gravity at the black hole’s horizon, and phenomena like frame dragging where black holes literally drag along the fabric of spacetime nearby, creating an environment where nothing is able to remain stationary relative to a distant observer like ourselves.

Watch the video below:

White dwarf binary provides unique natural laboratory for extreme physics

An international team led by astronomers at the University of Sydney has uncovered the clearest evidence yet for the origin of an unusual class of cosmic signals. In doing so, they have identified a rare stellar system that is providing scientists with a natural laboratory to study extreme physics.

Using CSIRO’s ASKAP radio telescope, the team discovered a small, dense star, called a white dwarf, shredding material from its larger, but less dense, companion star. As this material spirals in, it produces powerful bursts of radio waves and X-rays in a cycle that repeats every 1.4 hours.

The findings are published in Nature Astronomy.

Lead author and PhD student Kovi Rose from the University of Sydney’s School of Physics and CSIRO said this provides the first confirmed identification of what astronomers call ‘long-period radio transients’: cosmic pulses discovered from just a few remote regions of our galaxy.

“For the first time we have pinpointed the origin of these signals, confirming the source to be a ‘cataclysmic variable’, or an accreting white dwarf star,” said Mr Rose.

“Long-period radio transients have puzzled astronomers for years,” Mr Rose said. “We’ve only found about a dozen, and their origins have been unclear. Now, we’ve been able to show that the source for one of these transients comes from a white dwarf actively pulling material from a companion star.”

A rare and revealing system

The newly identified system, named ASKAP J1745−5051, consists of a white dwarf – a dense stellar remnant roughly the size of Earth but with the mass close to that of the Sun – paired with a larger but lower-mass red dwarf star of about one-tenth the Sun’s mass. The two stars orbit each other extremely closely, completing a full orbit in just over an hour.

As material from the less massive star is drawn towards the white dwarf, it heats up and emits X-rays. At the same time, interactions between the stars’ magnetic fields generate regular radio bursts, meaning the signal occurs at specific intervals.

“These emissions are all tied to the orbital motion of the system,” Mr Rose said. “But interestingly, the radio and X-ray signals don’t peak at the same time, which tells us they’re being produced in different regions of the system.”

The team found that the radio emission likely originates where the magnetic fields of the two stars meet and interact with the charged material being ripped from the companion star, producing tightly beamed bursts of radiation.

Solving a cosmic mystery

Long-period radio transients were initially thought to be slow-spinning neutron stars, known as pulsars. However, current models suggest neutron stars rotating this slowly should not be able to produce such signals.

The new discovery strengthens an alternative explanation: that at least some of these mysterious bursts come from systems of two stars, involving white dwarfs.

“Some similar objects had been linked to binary systems before, but this is the first one where we can clearly see both stars and the accretion process in action,” said Professor Murphy, Head of School at the University of Sydney School of Physics and Chief Investigator at the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav).

The system is also only the second known long-period radio transient to emit regular X-rays – and the first where the cause of the regularity has been confirmed.

A ‘Rosetta stone’ for future discoveries

This unique system was discovered using the ASKAP radio telescope, owned and operated by CSIRO, Australia’s national science agency. ASKAP’s mix of coverage, resolution, and sensitivity is unparalleled in radio astronomy, allowing for such unusual signals to be detected that would otherwise be missed.

The researchers say that ASKAP J1745-5051 could act as a reference point for understanding other long-period radio transients.

“This system gives us a way to decode these signals. It could help us determine whether other long-period transients are more like pulsars or like white dwarf systems, acting like a stellar Rosetta stone,” said Mr Rose, referring to the archaeological object discovered in Egypt that helped translate ancient hieroglyphics.

The discovery also provides a unique opportunity to study extreme plasma physics and magnetic interactions under conditions that cannot be replicated on Earth.

“These systems are natural laboratories,” Mr Rose said. “They allow us to test our understanding of how matter behaves in strong magnetic fields and under intense gravitational forces.”

Future research

The team plans further observations combining radio, optical and X-ray telescopes to better understand how these emissions are generated and whether similar mechanisms can explain the full population of long-period radio transients.

“Each new discovery is helping us piece together the bigger picture,” Mr Rose said. “We’re only just beginning to understand this new class of cosmic events.”

The international team included astronomers from the United States, China, Canada, Spain, Israel and Australia. The team used CSIRO’s Australia Telescope Compact Array and ASKAP radio telescopes in Australia, the MeerKAT radio telescope in South Africa, the SOAR and Magellan optical telescopes in Chile, and the space-based Swift (UV/X-ray) and Einstein Probe (X-ray) telescopes.

MEDIA ENQUIRIES: media.office@sydney.edu.au

Media Release prepared by Ivy Shih, Media and PR Adviser | University of Sydney

RESEARCH: Rose, K. et al ‘Periodic radio and X-ray emission from an accreting white dwarf binary’ (Nature Astronomy 2026). DOI: 0.1038/s41550-026-02882-x

Watch the explainer video below:

The LIGO-Virgo-KAGRA (LVK) Collaboration has today released its latest catalog of gravitational-wave detections. The data analysed for this update were collected by the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors and the Virgo detectors. They are the world’s premier observatory of gravitational waves, ripples in the fabric of spacetime.

This catalog aggregates hundreds of cosmic collisions between pairs of black holes, each producing a new, heavier black hole. These distant events provide a rich dataset for scientists to map out how the Universe builds black hole systems.

Using the new data, compiled in the Gravitational-Wave Transient Catalog (GWTC-5.0), scientists from the LVK collaboration and  the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) at Monash University, have identified clear evidence that black hole binaries are born in distinct sub-populations. Effectively, different cosmic assembly lines that operate in unique environments.

Project lead, Sharan Banagiri, a Research Fellow from Monash University’s School of Physics and Astronomy and OzGrav, used this data to observe the shared characteristics of colliding black holes and neutron stars.

“This set of nearly 400 gravitational-wave detections from LIGO and Virgo provides us with a clear indication that the binary black hole mergers we see are forming in several different ways. Some might form as one giant cloud of gas that collapses to give two massive stars that then become black holes. Others might be black holes that wander into each other in dense environments called clusters that are packed with stars. While others are the product of a previous generation of mergers between two black holes,” Dr Banagiri said.

The paper, released as a preprint, found that there is a presence of multiple sub-populations of merging black holes that can potentially arise from different formation pathways.

Assistant Professor of physics at Princeton University, Sylvia Biscoveanu, co-author of the study and previously a Fulbright postgraduate scholar at Monash University, commented on the unprecedented scale of the catalog update.

“GWTC-5 represents the largest single increase in the size of the gravitational-wave catalog, including events with remarkable properties such as GW241127, which contains BHs of very different masses with clearly wobbling orbits due to tilted spins. The new catalog also contains the event with the best localisation on the sky to date, GW240615.”

The researchers also found that some of these black holes are spinning very rapidly. These fast spinning black holes have two different sets of masses; the first set are between 10-20 times the sun’s mass and the second set have masses greater than 45 times the sun’s mass.

“One of the most fascinating things we’ve discovered about these new black holes is that they are spinning very fast. The sun rotates once every 25 days. If it became a black hole and started spinning as quickly as the ones we discovered, it would be rotating several thousand times every second. So where do these rapidly-spinning black holes come from? One leading explanation is that they are ‘hierarchical’ products of a previous generation of merger between two black holes,” Dr Banagiri said.

The paper identified that black holes which are hierarchical in origin, are more massive than other black holes nearby. By analysing the new data set, the researchers found that the black holes more massive than 45 times the sun, are more likely to merge with lower mass black holes.

The new dataset will provide rich new information about black holes for astronomers and scientists to research.

Chief Investigator at OzGrav and Professor of Physics and Astronomy at Monash University, Eric Thrane, said this is a milestone as gravitational-wave astronomy transitions from the discovery of individual events to the statistical profiling of cosmic population

“We are no longer just looking at individual anomalies, instead, we are seeing a true kaleidoscope of cosmic collisions. We are pushing the edges of what we know, seeing things that are more massive, spinning faster, and more unusual than ever before,” Professor Thrane said.

Read the research paper: https://dcc.ligo.org/LIGO-P2600045/public

MEDIA Release prepared by Monash University.

An international team of scientists from the LIGO, Virgo, and KAGRA collaborations, including researchers from the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav), has completed one of the most sensitive searches yet for continuous gravitational waves from young supernova remnants. 

 Neutron stars (NSs) are among the most exotic objects in the Universe. They are born when massive stars die in energetic explosions called core-collapse supernovae. These explosions rip the star apart and leave behind a beautiful diffuse nebula called a supernova remnant.  

“These objects are incredibly extreme environments,” said Dr Ornella Piccinni, from the University of the Balearic Islands and Associate Investigator at OzGrav, who led the study while at the Australian National University. “They give us a way to test physics in conditions we can’t reproduce on Earth.” 

NSs are also the strongest magnets in the Universe and can rotate astonishingly fast, with some rotating hundreds of times per second. Astrophysical estimates suggest that millions of NS may have formed in our Galaxy. However, only a fraction of neutron stars are observed as pulsars (they emit pulses of light). This lack of observation may be either because their emission beams do not intersect the Earth or because they have become too weak to detect. As a result, most neutron stars remain electromagnetically silent, and their internal properties are largely inaccessible even to the most sensitive telescopes. 

“Gravitational-wave signals from neutron stars are incredibly faint, which makes them difficult to detect,” said Dr Ling (Lilli) Sun. “But they carry unique information about the structure of neutron stars.” 

Continuous gravitational waves (CWs) provide a new tool to discover previously missed pulsars and unobserved NSs and probe their exotic interiors. 

In a recent paper, the team searched for continuous gravitational waves from 15 young to middle-aged supernova remnants, ranging from approximately 40 years old (SN 1987A) to tens of thousands of years old, 14 of which are in our galaxy and one in our neighbouring galaxy, the Large Magellanic Cloud. 

The search used eight months of data from May 2023 to Jan 2024 during the first phase of the detectors’ fourth observing run (O4a). 

While transient bursts of gravitational waves are now regularly observed, CWs are much harder to detect because these signals are expected to be far weaker than the bursts seen from neutron star or black hole mergers, often weaker by several orders of magnitude. 

But no detection does not mean there are no results. 

By measuring how sensitive the search was, the team was able to place the strongest limits so far on how strong these signals could be, improving on previous observing runs. These limits help narrow what scientists think neutron stars can look like, including how “bumpy” they are and how matter behaves under the most extreme conditions in the Universe. 

“Even when we don’t see a signal, we’re still learning,” said Yutong (Tracy) Bu from the University of Melbourne, who worked on the analysis. “We can place stronger constraints on what these neutron stars are doing.” 

These systems may host young neutron stars where the rotation frequency is still unknown. Their relatively young age implies that the neutron star candidates are more likely to have non-uniform deformations than older ones and emit stronger continuous gravitational waves. 

“We’re pushing the sensitivity of these searches further than ever before,” said Dr Piccinni. “Each step brings us closer to a detection.” 

These results are the most sensitive broadband frequency searches so far for continuous gravitational waves from supernova remnants. 

As data collection continues and sensitivity improves, researchers are closing in on the first detection of continuous gravitational waves — a breakthrough that would open an entirely new way of studying neutron stars. 

Watch the explainer video below:

An international team of scientists from the LIGO, Virgo, and KAGRA collaborations, including researchers from the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav), has shown for the first time that gravitational waves, ripples in space and time produced by some of the most violent events in the Universe, such as the collision of two black holes, can be used to measure and correct the calibration of the detectors that observe them.

The breakthrough comes from the study of two exceptionally strong gravitational-wave signals, known as GW240925 and GW250207, produced by the collisions of pairs of black holes and detected by the twin detectors of the US National Science Foundation Laser Interferometer Gravitational-wave Observatory (NSF LIGO). These events were so strong that they allowed researchers not only to study the black holes that created them, but also to check how accurately the detectors were recording the signals.

“In a way, we are using black holes to help check the accuracy of our detectors. How cool is that!” said Dr Ling (Lilli) Sun from the Australian National University.

Three OzGrav researchers from three different Australian universities played key scientific roles in the study. Dr Ling (Lilli) Sun from the Australian National University provided scientific leadership on the paper, while Mallika Sinha, a PhD student at Monash University, and Dr Yi Shuen Christine Lee, a Postdoctoral researcher at the University of Melbourne, made important contributions to the analysis and interpretation of the results.

The LIGO–Virgo–KAGRA collaboration has now confidently detected more than 200 gravitational-wave signals from merging black holes and neutron stars. Each signal carries information about its source and the extreme physics governing these collisions. Extracting that information requires the detectors to measure gravitational waves with extraordinary precision and to carefully account for any uncertainties in those measurements.

Gravitational waves stretch and squeeze spacetime as they pass through Earth. The detectors measure this by sending laser light down two perpendicular arms and looking for tiny differences in the time it takes the light to travel back and forth. A typical gravitational wave changes the arm length by about one ten-billionth of a billionth of a metre, smaller than the width of a proton.

“Thanks to major upgrades over the past decade, our detectors are now so sensitive that signals from colliding black holes come through loud and clear,” said Dr Sun. “If Einstein’s theory of general relativity is correct, those signals should follow a very specific pattern.”

Turning those minute measurements into a physical gravitational-wave signal requires a detailed model of the detector’s response. This includes accounting for the complex control systems used to keep the instruments stable. Normally, calibration uncertainties are measured and estimated using auxiliary lasers, sensors, and engineering data. However, during the detections of GW240925 and GW250207, the LIGO Hanford detector happened to have a larger calibration error than usual.

According to Dr Sun, “by comparing the predicted signal with what we actually record, we can spot tiny mismatches that sometimes reveal the detector wasn’t perfectly calibrated at the time.”

Because both signals were exceptionally loud, the researchers were able to disentangle the true gravitational-wave signal from the detector’s calibration error, a process known as astrophysical calibration. GW240925 served as a verification case, allowing the team to compare results from astrophysical calibration with data that was later corrected using standard methods.

GW250207, meanwhile, is the second-loudest gravitational-wave event ever observed and provides a unique window into extreme physics. For this event, astrophysical calibration was essential to ensure the data could be trusted at all.

Accurate calibration is critical because even small errors can bias estimates of key source properties, such as the masses of the black holes, whether they are spinning, and where the signal originated in the sky.

“It was simply bad luck that such a loud event was observed while LIGO Hanford was in an unsettled state,” said Mallika Sinha. “As our detectors become more sensitive and we observe more events, situations like this will only become more common. Without astrophysical calibration, we might not be able to reliably analyse these interesting events and miss out on some nifty science.”

The researchers found that GW240925 was produced by black holes around nine and seven times the mass of the Sun, while GW250207 involved black holes roughly 35 and 30 times the Sun’s mass.

“Using three detectors instead of two helps us pinpoint the location of gravitational-wave sources much more precisely, which also means we can better understand the physical properties of the sources themselves,” said Dr Yi Shuen Christine Lee.

“This successful astrophysical calibration using GW240925 and GW250207 is an exciting step forward for gravitational-wave astronomy. It improves our chances for extracting important astrophysical information from gravitational-wave sources, even when traditional detector calibration methods are not accurate or feasible!”

Because of its strength and position in the sky, GW250207 is considered one of the most promising gravitational-wave signals for future measurements of the Hubble constant, although many such “dark siren” events, gravitational-wave signals from black hole mergers that produce no visible light, will be needed to resolve the long-standing tension between different cosmological measurements.

Together, GW240925 and GW250207 mark the first successful tests of astrophysical calibration, a technique that could allow scientists to trust gravitational-wave data even when detectors are in an unsettled state.

As gravitational-wave astronomy moves from discovery to precision science, using the Universe itself to help calibrate our instruments may become an increasingly powerful tool.

Watch the explainer video below:

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Media Enquiries

Researchers from the study are available for interview.

For interview requests, additional information, or media enquiries, please contact:

Diana Haikal
Senior Communications and Engagement Advisor
ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav)
ozgrav.comms@swin.edu.au

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DOI: https://doi.org/10.1103/gzrj-mwv3

Physical Review Letters journal link:  https://journals.aps.org/prl/accepted/10.1103/gzrj-mwv3

 

 

 

An awe-inspiring new chapter in science engagement has begun, with Professor Matthew Bailes, Director of the ARC Centre of Excellence for Gravitational Wave Discovery, officially launching Swinburne Virtual Universe.

The space is exactly what it sounds like. A fully immersive room wrapped in more than 100 square metres of high-contrast LED screens, where you’re not just looking at the Universe, you’re inside it.

Visitors can move through a virtual solar system, guided in real time, with 3D visuals built from supercomputer simulations and real astrophysics data. It’s designed to make complex science feel intuitive, and honestly, a bit magical.

“It’s hard to describe that moment,” Professor Bailes said, reflecting on seeing Saturn’s rings stretch across the entire space. “You feel like you can walk along them and look out into infinity. That’s the feeling I want people to experience when they come in here.”

The idea for the Virtual Universe goes back much further. For Bailes, it traces all the way back to watching the Moon landing as a child and the sense of wonder that came with it. That same feeling is what this space is trying to recreate, not just for students, but for anyone who walks through the door.

Early reactions suggest it’s working.

From school students reaching out to grab floating moons, to adults completely absorbed in the experience, the Virtual Universe is already doing what it set out to do, connecting people to science in a way that sticks.

Built in partnership with OzGrav, the facility brings together research, technology and storytelling in one place. It also opens up new opportunities, not just for outreach, but for research translation and creative industries.

Now open, the Virtual Universe is already bringing in schools and the wider community, turning curiosity about space into something people can actually step inside and feel.

To learn more, visit www.svu3d.ai

Watch Professor Matthew Bailes speaking about SVU below:
Professor Matthew Bailes speaking about SVU

An international team of scientists led by the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) at Monash University has uncovered evidence of a rare form of exploding star, helping to shed light on one of the most cataclysmic events in the Universe.

At the end of their lives, most massive stars collapse into black holes – objects with gravity so strong that not even light can escape.

Some very massive stars, however, are expected to become so hot that they are blown apart in a pair-instability supernova – an explosion so intense that the star is completely disrupted, leaving behind no black hole.

First predicted in the 1960s, pair-instability supernovae are challenging to distinguish from more common stellar explosions that leave behind black holes.

In a study published in Nature, researchers found that by using gravitational waves – ripples in the fabric of spacetime detected by the LIGO-Virgo-KAGRA observatory network – they were able to measure the properties of black holes and found a “forbidden range” of black-hole masses.

Black holes with masses more than 45 times the mass of the sun are rare because the stars that might otherwise have made them exploded in pair-instability supernovae.

Project lead, Hui Tong, a PhD candidate from OzGrav at Monash University’s School of Physics and Astronomy, said the research found a forbidden mass range where stars seemingly don’t make black holes.

“The observation is well explained by pair instability; there are no stellar-origin black holes in the forbidden zone because stars are undergoing pair-instability supernovae. The only black holes in this mass range are made from merging smaller black holes, rather than directly from stars,” Mr Tong said.

Confirming the existence of this gap would help settle a major question about how the most massive stars live and die, and the origin of black holes.

Project collaborator, Professor Maya Fishbach from the University of Toronto and CITA said the study highlights the potential of gravitational waves to probe the lives, deaths and afterlives of the most massive stars in our Universe.

“We are seeing indirect evidence of one of the most titanic blasts in the cosmos: pair-instability supernovae. At the same time, we are finding that once they are born, black holes can grow via repeated mergers,” said Professor Maya Fishbach.

“It’s a cool result because we are using black holes to learn about the nuclear reactions inside stars,” said Professor Eric Thrane, Chief Investigator at OzGrav.

Read the research paper: https://doi.org/10.1038/s41586-026-10359-0

Watch our explainer video below: