Congratulations to OzGrav Associate Investigator Matt Dodds, recipient of the 2025 Prime Minister’s Prize for Excellence in Science Teaching in Secondary Schools.
The ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) proudly celebrates Matt’s national recognition for his creative and hands-on approach to science teaching, bringing physics to life for students in regional and remote communities.
“I’m passionate about teaching in regional Australia,” Matt says. “Just because we’re in rural areas doesn’t mean students shouldn’t have access to high-quality STEM experiences.”
Since 2018, Matt has worked closely with OzGrav’s Education and Outreach team, helping translate complex astrophysical concepts into engaging, real-world classroom experiences. Collaborating with OzGrav’s Senior Education and Outreach Manager, Jackie Bondell, he has co-developed national teacher workshops, student outreach programs, and public events that have reached thousands of participants across Australia.
“Matt’s passion for physics and astronomy is infectious,” says Bondell. “He’s taken OzGrav’s outreach tools, from VR experiences to LEGO® interferometers, and shared them with students and teachers across Australia. He has an extraordinary gift for making science accessible and exciting.”
Among his many innovations, Matt created a LEGO® DUPLO® Interferometer, a hands-on model that demonstrates the principles behind gravitational-wave detection. Developed in collaboration with OzGrav, the design has been adopted across OzGrav’s eight nodes and even features in outreach programs at LIGO in the United States and KAGRA in Japan.
“It’s amazing to see a simple LEGO model spark such curiosity,” says Matt. “It helps students visualise how instruments like LIGO detect ripples in spacetime and shows that anyone can explore big scientific questions with the right mindset.”
Matt, a Physics and Biology teacher at Glen Innes High School (NSW), has made contributions that extend well beyond his classroom. He established the Astronomy and Astrophysics Depth Study Program at Siding Spring Observatory, now in its seventh year and attended by more than 280 students from regional NSW schools. His inventive lessons, such as using data from NASA’s Kepler Telescope to calculate the mass of stars or designing solid-fuel rockets using CAD simulations, have been adopted by physics teachers worldwide. He also mentors educators across Australia, sharing creative approaches such as smartphone spectroscopes and Hot Wheels-based demonstrations of projectile motion.
“Students are inspired when they see their teachers still learning,” Matt says. “Science is about curiosity that never ends.”
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 detected two remarkable black hole collisions that are offering new insights into both the evolution of the cosmos and the nature of dark matter.
The pair of gravitational-wave events, named GW241011 and GW241110, were detected in late 2024, just one month apart, during the O4b observing run of the global detector network. Each signal was produced by the violent merger of two black holes, forming an even more massive remnant and sending ripples through space-time, each travelling for hundreds of millions to billions of years before reaching Earth.
GW241011 and GW241110 infographic. Credit: Shanika Galaudage / @astronerdika
Both events involved unequal-mass, rapidly spinning black holes, an unusual combination that provides a window into how black holes form and evolve, and how they can be used to test new physics. Using these signals, researchers from OzGrav and the Australian National University (ANU) investigated whether the black holes’ spins could reveal hints of previously undiscovered particles.
OzGrav PhD student Aswathi Pampurayath Subhash from the Australian National University led the analysis focusing on ultralight bosons, hypothetical particles that could make up dark matter. Certain theories suggest these particles might gradually drain rotational energy from black holes over time. But since the black holes in GW241011 and GW241110 were still spinning rapidly when they merged, scientists were able to rule out a wide range of possible boson masses, tightening the constraints on dark matter theories.
“Rapidly spinning black holes like those in GW241011 and GW241110 are more than just astrophysical curiosities; they can be used to test the existence of new particles,” said Aswathi Pampurayath Subhash. “By remaining highly spinning over their long lifetimes, they allow us to rule out a wide range of possible ultralight boson masses, placing new constraints on dark matter and theories beyond the Standard Model.”
The data also shed light on how black holes grow and evolve. Both mergers involved one black hole roughly twice as massive as the other, and both showed signs that their spins were tilted compared to the direction of their orbits. This misalignment hints that the systems may not have formed from two stars evolving together, but instead through repeated mergers inside dense star clusters, a process known as hierarchical merging.
“These two black hole mergers give us a remarkable glimpse into how black holes grow and evolve,” said Dr Ling (Lilli) Sun from the Australian National University and Chief Investigator at OzGrav. “Their high spins and unequal masses suggest that they may be second-generation black holes, the products of earlier mergers in dense stellar environments, such as star clusters. Each detection adds a new piece to the puzzle of how the most extreme objects in our universe come to be.”
The detections highlight the extraordinary sensitivity of the LIGO, Virgo, and KAGRA observatories, which continue to uncover the hidden stories of the Universe’s most extreme objects. “Each new discovery not only deepens our understanding of black hole formation but also transforms these cosmic collisions into laboratories for fundamental physics,” says OzGrav Chief Investigator Professor Eric Thrane from Monash University.
Together, GW241011 and GW241110 showcase the remarkable progress of gravitational-wave astronomy in revealing the hidden lives of merging black holes. Each detection brings us closer to understanding how these cosmic giants form and evolve, while offering a powerful way to test the fundamental laws that govern the Universe itself.
Check out the explainer video below about the twin black hole mergers:
Information about OzGrav and gravitational-wave observatories:
This material is based upon work supported by NSF’s LIGO Laboratory which is a major facility fully funded by the National Science Foundation. NSF’s LIGO Laboratory is a major facility fully funded by the National Science Foundation and operated by Caltech and MIT, which conceived of LIGO and led the Initial and Advanced LIGO projects. Financial support for the Advanced LIGO project was led by the NSF with Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council) and Australia (Australian Research Council-OzGrav) making significant commitments and contributions to the project. More than 1600 scientists from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration. A list of additional partners is available at https://my.ligo.org/census.php.
The Virgo Collaboration is currently composed of approximately 880 members from 152 institutions in 17 different (mainly European) countries. The European Gravitational Observatory (EGO) hosts the Virgo detector near Pisa in Italy, and is funded by Centre National de la Recherche Scientifique (CNRS) in France, the Istituto Nazionale di Fisica Nucleare (INFN) in Italy, and the National Institute for Subatomic Physics (Nikhef) in the Netherlands. A list of the Virgo Collaboration groups can be found at: https://www.virgo-gw.eu/about/scientific-collaboration/. More information is available on the Virgo website at https://www.virgo-gw.eu.
KAGRA is the laser interferometer with 3 km arm-length in Kamioka, Gifu, Japan. The host institute is Institute for Cosmic Ray Research (ICRR), the University of Tokyo, and the project is co-hosted by National Astronomical Observatory of Japan (NAOJ) and High Energy Accelerator Research Organization (KEK). KAGRA collaboration is composed of over 400 members from 128 institutes in 17 countries/regions. KAGRA’s information for general audiences is at the website https://gwcenter.icrr.u-tokyo.ac.jp/en/. Resources for researchers are accessible from http://gwwiki.icrr.u-tokyo.ac.jp/JGWwiki/KAGRA.
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)
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)]
2025 Frontiers of Science Award for the international Double Pulsar research team
The research paper “Strong-Field Gravity Tests with the Double Pulsar” led by OzGrav Partner Investigator Michael Kramer (Max Planck Institute for Radio Astronomy, MPIfR) and including OzGrav Chief Investigator Adam Deller (Swinburne University) along with an international research team was published in the journal “Physical Review X” (Kramer et al. 041050, December 13, 2021). Their work received the Frontiers of Science award within the category “Astrophysics and Cosmology – theory” from the International Congress for Basic Science (ICBS). The award ceremony took place at the China National Conference Center (CNCC) – on July 13, 2025.
More than 100 years after Albert Einstein presented his theory of gravity, scientists around the world continue to search for tiny deviations from its predictions that would point the way to a new theoretical understanding of the laws that govern the Universe. Binary radio pulsars – rapidly spinning neutron stars whose beamed radio emission can be observed as precise clock ticks from the Earth – are ideal laboratories for searching for such deviations. The “double pulsar” system, which was the subject of the paper honoured by the ICBS, is the best such system currently known for making these ultra precise tests. “We studied a system of very compact stars to test gravity theories in the presence of very strong gravitational fields,”, states the research team’s leader, Michael Kramer from the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, Germany. “To our delight we were able to test a cornerstone of Einstein’s theory, the energy carried by gravitational waves, with a precision that is 25 times better than with the Nobel-Prize winning Hulse-Taylor pulsar.”
Apart from the loss of orbital energy through gravitational waves, other relativistic effects such as the periastron advance of the system (which has precessed around a full turn since its discovery over 20 years ago!), relativistic time dilation, and spacetime curvature have all been precisely measured in the double pulsar system, with every result agreeing with Einstein’s predictions to within the measurement uncertainty.
Such tests are only possible through careful calibration of the observed pulsar “clock ticks” for other effects that are unrelated to general relativity. As one example, the motion of the pulsar relative to the Earth, and its acceleration in the gravitational field of the Milky Way, contribute to the observed change in its orbital period. Fortunately, these effects can be calculated and corrected if the distance to the double pulsar and its motion on the sky are known. Prof Adam Deller led additional observations that measured tiny shifts in the position of the double pulsar system on the sky to provide these corrections. “By measuring how the double pulsar’s position shifted over the course of a year as the Earth orbits the Sun, we can infer how distant it is” said Prof. Deller. “But the position shifts are tiny – like seeing an ant crawl around a button from 5,000 km away!”
This combination of diverse effects produced by a system of two strongly self-gravitating bodies with extreme spacetime curvature makes the Double Pulsar a unique testbed — not only for general relativity but also for various competing theories, some of which have been significantly constrained or even excluded by this experiment.
“We are very pleased with the award honouring our work with the Double Pulsar which is the result of a collaboration with great colleagues, who together allowed us to combine our precision experiments with a rigorous theoretical understanding,” concludes Michael Kramer.
Marta Burgay (left) and Michael Kramer (right) receiving the 2025 Frontiers of Science Award on behalf of all the authors of the Kramer et al. (2021) Double Pulsar paper. Credit: ICBS
Original Paper
Kramer et al. Strong-Field Gravity Tests with the Double Pulsar, 2021, Physical Review X, December 13, 2021 (DOI: 10.1103/PhysRevX.11.041050).
Gravitational waves from record‑breaking black holes challenge current astrophysical models
The LIGO-Virgo-KAGRA (LVK) Collaboration has observed the heaviest black‑hole merger ever detected, registering gravitational waves from two rapidly spinning giants that coalesced into a single black hole about 225 times the mass of our Sun. Designated GW231123, “GW” for gravitational wave and “231123” for the detection date 23 November 2023, the signal was captured during the fourth LVK observing run and publicly released on Monday, 14 July 2025.
“This collision is so distant that the ripples we’re measuring began their journey billions of years ago, long before dinosaurs walked the Earth,” says Professor Eric Thrane, OzGrav Chief Investigator at Monash University. “Yet that tenth of a second blip forces us to rethink how very heavy, rapidly spinning black holes come to be.”
GW231123 involved black holes of roughly 100 M☉ and 140 M☉, far beyond the masses predicted by standard stellar evolution theory. Their extreme spin hints that these monsters may have grown through successive mergers rather than a single stellar collapse.
An infographic detailing the new GW231123 black hole merger. Credit- Simona J. Miller, Caltech
“Their spin is near the limit of what’s physically possible,” Thrane explains. “Observing two black holes whirling so fast when they merge tells us something, either they were born spinning like tops, or something in their lives wound them up to these incredible speeds.”
Unravelling the short, complex GW231123 signal stretched detection hardware and waveform modelling to their limits. Since LIGO’s first discovery in 2015, the LVK network has catalogued ≈300 black‑hole mergers, more than 200 of them in the current observing run alone.
“Gravitational wave astronomy is barely ten years old,” Thrane notes. “Each observing run delivers discoveries that would have been science fiction a decade ago, and this latest event is our most dramatic example yet.”
The calibrated data for GW231123 are now public via the Gravitational‑Wave Open Science Centre (GWOSC), enabling researchers worldwide to probe whether heavy, fast‑spinning black holes form a new population or point to physics beyond current models.
“Maybe this is just the tip of the iceberg,” Thrane says. “If these heavyweight speed demons are common, we could be on the verge of a major leap in our understanding of how the Universe makes, and remakes, black holes.”
Initial results, released on the arXiv, were presented at the joint GR24 and Amaldi16 gravitational-waves meeting in Glasgow, UK, on 14 July.
Astronomers have detected an ultra-bright burst of radio waves from Relay 2, a NASA communications satellite launched in 1964 and silent since 1967. OzGrav Chief Investigator Adam Deller, Professor of Astrophysics at Swinburne University of Technology, was one of the principal authors of the discovery recently accepted for publication in the Astrophysical Journal Letters.
NASA’s Relay 2 spacecraft orbits between 2,091 km and 7,411 km above Earth, and has been offline since 1967. Credit: NASA
“This was a chance discovery made when looking for Fast Radio Bursts, which are millisecond-duration radio pulses that originate in distant galaxies. Despite FRBs being discovered almost 20 years ago, we still don’t know what can generate such short and bright radio emission, which is what is driving us to build better and better machines for finding them,” said Prof Deller.
The pulse, captured on 13 June 2024 by the CRACO upgrade on CSIRO’s ASKAP radio telescope on Wajarri Yamaji Country in Western Australia, lasted under 30 nanoseconds, more than a million times shorter than the blink of an eye. However, the fact that it was so much shorter than a typical FRB wasn’t immediately apparent.
“FRBs are intrinsically very brief flashes, but the radio pulse is spread out in frequency by the time they get to us on Earth. Longer wavelengths travel more slowly when passing through the ionised plasma in interstellar space, and so this millisecond pulse gets spread out by the time it reaches us, with the lower frequencies arriving hundreds of milliseconds to seconds later,” explained Prof Deller. “We can only correct for this spreading out roughly when doing the high-speed search for FRBs, but once we find a candidate, we can go back and find the absolute best correction, along with the true duration of the signal.”
Because the Relay 2 signal showed virtually no dispersion in frequency, researchers immediately suspected a nearby origin rather than a distant galaxy. ASKAP imaging confirmed the burst came from roughly 4,500 km away—the satellite’s position at the moment of detection.
The team’s pre-print, A nanosecond-duration radio pulse originating from the defunct Relay 2 satellite, outlines two likely causes: an electrostatic discharge (ESD) triggered by charge build-up on the spacecraft, or a fleeting plasma cloud created by a micrometeoroid impact. Either mechanism poses a recognised threat to operational satellites.
“We were lucky to see it. It is certainly possible that there are many more such bursts happening from this or other satellites. However, in the detailed search that we can do with our ASKAP data, we wouldn’t mistake these as actual FRBs—the lack of spreading out of the signal in frequency is a dead giveaway,” said Prof Deller.
Beyond protecting spacecraft electronics, studying nanosecond-scale ‘sparks’ can also help astronomers filter out false positives when hunting for genuine cosmic FRBs.
“It was so totally unexpected to see such a short and bright radio pulse originating from a non-operational satellite – we’re both excited to see if this can be of use for identifying hazards for operational satellites, and hopeful that we can use what we learned to further improve the robustness of our FRB searches,” added Prof Deller.
Collaboration
The lead author of the paper is Dr Clancy James (Curtin University node, International Centre for Radio Astronomy Research), while other OzGrav contributors include Chief Investigator Prof. Ryan Shannon.
This work leverages the Commensal Real-time ASKAP Fast Transients (CRAFT) survey’s ability to produce rapid, high-resolution images—technology designed for deep-space FRB searches but now proving invaluable closer to home.
ASKAP is part of the Australia Telescope National Facility and operates with generous support from the Wajarri Yamaji People, the Australian Government and the Pawsey Supercomputing Research Centre.
Paper: James C. W. et al. (2025) A nanosecond-duration radio pulse originating from the defunct Relay 2 satellite (arXiv:2506.11462).
Information reproduced in part courtesy of Charlene D’Monte, ICRAR.’Monte, ICRAR.
Astronomers from the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) and the International Centre for Radio Astronomy Research (ICRAR), in collaboration with international teams, have made a startling discovery about a new type of cosmic phenomenon.
The object, known as ASKAP J1832-0911, emits pulses of radio waves and X-rays for two minutes every 44 minutes.
This is the first time objects like these, called long-period transients (LPTs), have been detected in X-rays. Astronomers hope it may provide insights into the sources of similar mysterious signals observed across the sky.
The team discovered ASKAP J1832-0911 by using the ASKAP radio telescope on Wajarri Country in Australia, owned and operated by Australia’s national science agency, CSIRO. They correlated the radio signals with X-ray pulses detected by NASA’s Chandra X-ray Observatory, which was coincidentally observing the same part of the sky.
“Discovering that ASKAP J1832-0911 was emitting X-rays felt like finding a needle in a haystack,” said lead author Dr Ziteng (Andy) Wang from the Curtin University node of ICRAR.
“The ASKAP radio telescope has a wide field view of the night sky, while Chandra observes only a fraction of it. So, it was fortunate that Chandra observed the same area of the night sky at the same time.”
LPTs, which emit radio pulses that occur minutes or hours apart, are a relatively recent discovery. Since their first detection by ICRAR researchers in 2022, ten LPTs have been discovered by astronomers across the world.
Currently, there is no clear explanation for what causes these signals, or why they ‘switch on’ and ‘switch off’ at such long, regular and unusual intervals.
“This object is unlike anything we have seen before,” Dr Wang said.
“ASKAP J1831-0911 could be a magnetar (the core of a dead star with powerful magnetic fields), or it could be a pair of stars in a binary system where one of the two is a highly magnetised white dwarf (a low-mass star at the end of its evolution).”
However, even those theories do not fully explain what we are observing. This discovery could indicate a new type of physics or new models of stellar evolution.”
Detecting these objects using both X-rays and radio waves may help astronomers find more examples and learn more about them.
According to second author Professor Nanda Rea from the Institute of Space Science (ICE-CSIC) and Catalan Institute for Space studies (IEEC) in Spain, “Finding one such object hints at the existence of many more. The discovery of its transient X-ray emission opens fresh insights into their mysterious nature,”
“What was also truly remarkable is that this study showcases an incredible teamwork effort, with contributions from researchers across the globe with different and complementary expertise,” she said.
The discovery also helps narrow down what the objects might be. Since X-rays are much higher energy than radio waves, any theory must account for both types of emission – a valuable clue, given their nature remains a cosmic mystery.
The International Centre for Radio Astronomy Research (ICRAR) is a joint venture between Curtin University and The University of Western Australia, with support and funding from the State Government of Western Australia. ICRAR is an internationally renowned research centre in radio astronomy, helping to build and support the world’s most powerful radio telescope.
Chandra X-ray Observatory
NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program. The Smithsonian Astrophysical Observatory’s Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.
It’s one of the first things any of us learn about astronomy – stars twinkle while planets don’t. However, other point-like objects in the radio sky also twinkle, or “scintillate,” including spinning neutron stars known as pulsars. A team led by Australian scientists has used a scintillating pulsar to perform tomography of the interstellar medium in our galaxy, mapping previously unseen layers of plasma, including within a rare structure called a bow shock.
Artist’s impression of a pulsar bow shock scattering a radio beam. Credit: Carl Knox / Swinburne / OzGrav
The discoveries, published today in Nature Astronomy, challenge existing theories of our local interstellar medium and will lead to new models for pulsar bow shocks.
The study, led by Dr Daniel Reardon from the ARC Centre of Excellence for Gravitational Discovery and Swinburne University of Technology, is the culmination of over 80 hours of observing the nearest and brightest millisecond pulsar to Earth using MeerKAT, the most powerful radio telescope in the Southern Hemisphere, located in South Africa.
While pulsars emit radio waves rather than visible light (like stars), they still “twinkle” because of turbulence in the plasma that exists in the space between stars. “This plasma is created from gas that is heated and stirred up by energetic events in our galaxy, like exploding stars,” Dr Reardon said.
“When a pulsar scintillates, it reveals valuable information about the location, structure, and motion of the plasma, as well as about the dynamics of the pulsar—we use scintillation to get unique insights.”
The observed pulsar, J0437-4715, is located relatively nearby to our solar system, within an area of our galaxy called the Local Bubble—a region almost devoid of gas and dust, created by the explosions of 15 stars about 14 million years ago.
Using the data gleaned from MeerKAT, the scientists studied patterns called “scintillation arcs,” which provide a tomographic map of plasma structures in the galaxy that are impossible to study using other methods. “These scintillation arcs revealed an unexpected abundance of compact plasma structures within our Local Bubble, which was thought to be more diffuse,” Dr. Reardon said.
For the first time, the team also used scintillation to study the bow shock created by the pulsar as it moves supersonically through the interstellar medium. “Travelling at Mach 10, the pulsar and its energetic wind of fast-moving particles create a shock wave of heated gas.”
This bow shock has been photographed as the energy of the supersonic pulsar heats Hydrogen enough for it to glow red. Yet while most pulsars should create bow shocks, only about a dozen have ever been observed because they are so faint. This study marks the first time scientists have been able to peer inside a pulsar bow shock to measure plasma speeds. “To our surprise, the scintillation arcs revealed multiple plasma layers inside the shock, including a structure moving towards the front of the shock,” Dr Reardon said.
This groundbreaking study, made possible by the pulsar’s closeness to Earth and the capacity of the MeerKAT telescope, achieved several significant firsts including a measurement of the three-dimensional shape of a bow shock, measurement of plasma speeds inside the shock, and the most detailed view of plasma structures within our Local Bubble. “We can learn a lot from a twinkling pulsar!”
An international team of astrophysicists from China and Australia, led by former Australian Research Council (ARC) Centre of Excellence for Gravitational-wave Discovery (OzGrav) researcher Prof. Xingjiang Zhu (now a Professor at Beijing Normal University, China), has for the first time determined how massive neutron stars are when they are born.
“Understanding the birth masses of neutron stars is key to unlocking their formation history,” said Dr. Simon Stevenson, an OzGrav researcher at Swinburne University and co-author of the study. “This work provides a crucial foundation for interpreting gravitational wave detections of neutron star mergers.”
Neutron stars are the dense remnants of massive stars, more than 8 times as massive as our Sun, born at the end of their lives in a brilliant supernova explosion.
These incredibly dense objects have masses between one and two times the mass of our Sun, compressed into a ball the size of a city, with a radius of just 10 km.
We can usually only weigh a neutron star (measure how massive it is) when it is in a binary star system with another object, such as a white dwarf or another neutron star. However, in these systems, the first-born neutron star typically gains extra mass from its companion, through a process called accretion, making it difficult to determine its original birth mass.
The research, published in Nature Astronomy, analyses a sample of 90 neutron stars in binary star systems with accurate mass measurements to measure the distribution of neutron star masses at birth, accounting for the mass gained since birth for each neutron star in a probabilistic manner.
The team found that neutron stars are typically born with a mass of around 1.3 times the mass of the sun, with heavier neutron stars being born more rarely.
“Our approach allows us to finally understand the masses of neutron stars at birth, which has been a long-standing question in astrophysics,” said Prof. Zhu.
The key plot from the paper, showing the inferred birth mass distribution of neutron stars
This finding is important for interpreting new observations of neutron star masses from gravitational wave observations.
The team used Bilby, a software package that OzGrav researchers developed to model neutron star mass distributions. The study’s Australian co-authors are members of the Australian Research Council (ARC) Centre of Excellence for Gravitational-wave Discovery (OzGrav).
To learn more about this discovery, watch Dr. Kirsten Banks interview Dr. Simon Stevenson below!
