Author: Diana Haikal

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:

Australia may be far from the world’s seismic hotspots, but a team from the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) at the Australian National University (ANU) is leading a breakthrough that could transform how earthquakes and tsunamis are detected worldwide. With $671,000 in new funding from the Australian Research Council’s (ARC) Discovery Projects (DP) scheme, Professor Bram Slagmolen and colleagues are developing technology capable of detecting earthquakes almost as soon as they happen at the speed of light.

When earthquakes strike, devastation can unfold in minutes or even seconds. Current early warning systems, such as those in Japan, rely on networks of seismometers to detect seismic waves. While effective, these systems can only provide limited notice, as seismic waves travel comparatively slowly through the Earth.

Professor Slagmolen explained the stakes “Our work focuses on creating early warning systems that could provide precious seconds for earthquakes and valuable minutes for tsunamis, allowing more time to safeguard lives, halt hazardous activities, and protect vital infrastructure such as power stations and gas pipelines.”

Those seconds matter. Extra lead time could allow high-speed trains to decelerate safely, surgeons to pause delicate procedures, or operators to shut down power grids in controlled ways. For tsunamis, additional minutes could mean entire coastal communities have time to evacuate.

So how does it work? The key lies in detecting prompt elasto-gravity signals, tiny changes in gravity generated the instant a fault ruptures in the Earth. Unlike seismic waves, which move at the speed of sound in rock, gravitational changes propagate at the speed of light.

Professor Robert Ward, OzGrav node leader at ANU, likens it to watching someone swing an axe across a field: you see the movement instantly, but the sound of the strike takes seconds to reach you. The gravitational “signal” arrives first, and with the right sensors, it can be measured before the destructive shaking begins. “Much of this system has been designed and fabricated here at ANU, it’s a huge engineering effort, and now we’re entering the phase of commissioning and testing.”

The team has already built and tested a prototype sensor. Now, they are installing it on a sophisticated seismic isolation platform, similar to those used in gravitational-wave observatories like Virgo in Italy and KAGRA in Japan, to filter out local vibrations and allow the sensor to focus only on gravitational changes.

Although Australia is not earthquake-prone, its scientists are global leaders in gravitational-wave detection, a field that requires ultra-sensitive instruments capable of measuring minuscule distortions in space-time. That expertise provides a unique advantage for tackling the challenge of gravitational earthquake detection.

“Australia may not experience major earthquakes, but we have world-class expertise in gravitational-wave detection, and that makes us uniquely placed to lead this research,” said Ward.

International collaboration is essential to the project’s success. Researchers in Japan and Switzerland are already testing smaller-scale versions of the sensor for both earthquake research and fundamental physics experiments. These partnerships ensure that the technology is not only refined in Australia but also tested in regions where earthquakes are more frequent, accelerating its path toward real-world deployment.

The coming years will focus on commissioning the upgraded sensor system and validating its performance. If successful, the technology could become an integral part of next-generation early warning systems, providing unprecedented speed and reliability.

For Ward, the ultimate goal is clear: “Ultimately, this technology could help solve a global problem: giving communities precious time to prepare before an earthquake or tsunami strikes.”

By uniting physics, engineering, and international cooperation, the ANU-led team is charting a path toward safer, more resilient societies. Their work demonstrates the power of fundamental research to address urgent global challenges.

Last week, the Australian gravitational-wave community gathered at Swinburne University to celebrate a landmark moment in science, the 10-year anniversary of the first direct detection of gravitational waves (GW150914). This discovery, announced in 2016 from data recorded on 14 September 2015, confirmed Einstein’s prediction and opened an entirely new window on the Universe.

The two-day workshop, hosted by the Australian Research Council Centre of Excellence for Gravitational Wave Discovery (OzGrav), brought together more than 80 students, researchers, and leaders from across the country. The workshop was more than just a commemoration of GW150914, it was a chance to reflect on Australia’s pivotal role in that discovery, to celebrate the remarkable advances of the past decade, and to look forward to what the next decade of gravitational-wave science will bring.

OzGrav’s Director, Professor Matthew Bailes, reflected on the impact of that first signal: “When the first detection happened in 2015, it completely transformed the landscape. Suddenly, gravitational-wave astronomy was real, and Australia needed a Centre of Excellence dedicated to it and that’s how OzGrav was born in 2017.” He added, “Since then, we’ve captured neutron star mergers in both gravitational waves and light, pushed quantum noise limits, and pioneered squeezed-light technology.”

For many in the room, it was collaboration that defined the journey. As Distinguished Professor Susan Scott, from the Australian National University, reminded the audience, “The first detection was only possible through collaboration and that spirit continues to drive gravitational-wave science forward.”

The workshop program reflected that spirit, spanning technical advances, new discoveries, and emerging projects, while also acknowledging the teamwork and persistence that made it all possible.

The celebration was about the future as much as the past. Day two highlighted the next generation of detectors and discoveries with Professor Paul Lasky from Monash University summing up the mood with optimism, “The gravitational-wave future is loud, much louder than GW150914. Every increase in sensitivity lets us hear further into the universe.” He also issued a call to action: “If we want an observatory in Australia, we will need ambition and collaboration to make it happen.”

Over coffee breaks, panel discussions, and even a celebratory cake, there was a palpable sense of both gratitude and anticipation. The workshop marked not only ten years since a signal that changed the world but also the strength of a community that has grown around it, a community ready to take the next bold steps into the cosmos.

Thank you to the local organising committee:

• Jade Powell, Diana Haikal, Kirsten Banks, Jackie Bondell, Carl Knox (Swinburne University of Technology)

• Susan Scott (ANU)

• Christine Lee (University of Melbourne)

  

Binary stars everywhere: Monash University scientists help rewrite cosmic origin story

A new international study, published in Nature Astronomy, reveals that massive stars are about as likely to form in close binary systems in the low-metal environments of the early Universe as they are today,  reshaping our understanding of stellar evolution and the origins of gravitational wave events.

The research, led by a global team of astronomers and using the European Southern Observatory’s Very Large Telescope in Chile, studied 139 O-type stars in the Small Magellanic Cloud, a nearby dwarf galaxy with just one-fifth the metallicity of our Sun. The findings challenge previous observations that low-mass stars are more likely to be found in binaries in metal-poor environments than in our Galaxy.

Professor Ilya Mandel, from the Monash University School of Physics and Astronomy, and the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav), co-authored the study, contributing to the statistical analysis testing whether the abundance of binary stars changes with metallicity, the chemical richness of the stars’ environment.

“Our analysis shows there’s no significant change in the fraction of massive stars in close binaries in metal-poor galaxies like the Small Magellanic Cloud,” said Professor Mandel. “That’s exciting, and it tells us that massive binary formation is a fundamental feature of star formation, even in the early Universe.”

The study found that around 70 per cent of the observed O-type stars are in close binaries, and two thirds of them will interact with a companion during their lifetimes, often leading to dramatic phenomena such as supernovae, black holes, or neutron star mergers.

“This is important because binary star interactions are a key pathway to producing exciting and rare outcomes, such as black holes and neutron stars that collide and emit gravitational waves,” Professor Mandel said. “Understanding how common these binaries are in different environments helps us predict how often we should expect to detect gravitational wave events, not just today, but across cosmic history.”

The discovery has far-reaching implications. It strengthens the case that many of the gravitational wave signals detected by LIGO and Virgo come from binary systems born in the early Universe. It also suggests that binary interactions likely played a large role in shaping galaxies and enriching them with heavy elements.

“By studying how stars evolve in environments that mimic the early cosmos, we get a clearer view of how black holes form, how galaxies evolve, and how the Universe became what it is today,” said Professor Mandel.

The research is part of the Binarity at LOw Metallicity (BLOeM) survey, and brings together more than 70 scientists across Europe, the US, Australia, and Israel.

Professor Mandel said the study exemplifies the power of international collaboration and big data analysis in unlocking the secrets of the cosmos.

“We’re in a golden age of discovery,” he said. “And what we’re learning now will echo in our understanding of the Universe for decades to come.”

Scientific paper
A high fraction of close massive binary stars at low metallicity. By: Hugues Sana, Tomer Shenar, Julia Bodensteiner, et al. In: Nature Astronomy, 2 September 2025. [original | preprint (pdf)]

Monash University media release: https://www.monash.edu/science/news-events/news/2025/binary-stars-everywhere-monash-university-scientists-help-rewrite-cosmic-origin-story