Author: Diana Haikal

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!” 

Read more via The Conversation: https://theconversation.com/twinkling-star-reveals-the-shocking-secrets-of-turbulent-plasma-in-our-cosmic-neighbourhood-243022

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.

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!

Paper published in Nature Astronomy

https://www.nature.com/articles/s41550-025-02487-w

Zhi-Qiang You, Xingjiang Zhu et al.

Preprint link: https://arxiv.org/abs/2412.05524

Media Contact

Email: ozgrav.comms@swin.edu.au

Available for interview 

Dr Simon Stevenson | ARC DECRA Fellow, Swinburne University of Technology

Dr Lilli Sun  | ARC DECRA Fellow, Australian National University (ANU)

Professor Eric Thrane  | Monash University

Research led by OzGrav PhD student Yu Wing Joshua Lee and supervisor Dr Manisha Caleb at the University of Sydney has uncovered the slowest cosmic lighthouse yet – a long-period radio transient – likely a neutron star – spinning once every 6.5 hours. This discovery, found using CSIRO ASKAP radio telescope and published in Nature Astronomy, not only pushes the boundaries of what we thought possible for such objects, which typically rotate very quickly, but also reveals a rare phenomenon: the ability to see radio pulses from both of the star’s magnetic poles. 

Find out more about their discovery in their paper published in Nature Astronomy now: https://www.nature.com/articles/s41550-024-02452-z

 You can also read about it in The Conversation: https://theconversation.com/blinking-radio-pulses-from-space-hint-at-a-cosmic-object-that-shouldnt-exist-246663 

Watch Joshua Lee discuss this discovery with Dr Kirsten Banks in the video below:

OzGrav is thrilled to congratulate Distinguished Professor Susan Scott on being awarded the George Szekeres Medal, the Australian Mathematical Society’s most prestigious honour. This award recognises outstanding contributions to the mathematical sciences, cementing Susan’s status as a leader in her field.

The medal was presented by Jessica Purcell, President of the Australian Mathematical Society, during the opening ceremony of the joint meetings of the Australian, American, and New Zealand Mathematical Societies in Auckland.

This historic win marks a series of firsts and milestones:

• Susan is the third woman in Australia to receive the medal.
• She is the first woman from the Australian National University (ANU) to achieve this recognition.
• She is only the second person from ANU ever awarded this honour.

A pioneer in gravitational wave theory and mathematical physics, Susan’s groundbreaking work has influenced the global scientific community and inspired a new generation of researchers.

The George Szekeres Medal, named after the celebrated mathematician, is a testament to Susan’s unwavering dedication to advancing mathematical sciences. Her work embodies the very essence of innovation and excellence.

We are incredibly proud to celebrate this well-deserved recognition of Susan’s remarkable career. Watch the video below where Susan shares her journey and reflections on this significant achievement.

Congratulations, Susan!

Image Credit: Australian Mathematical Society

An international study led by astronomers from Swinburne University of Technology and Monash University has created the most detailed maps of gravitational waves across the universe to date.

The study also produced the largest ever galactic-scale gravitational wave detector and found further evidence of a “background” of gravitational waves: invisible yet incredibly fast ripples in space that can help unlock some major mysteries of the universe.

This international effort, conducted with the MeerKAT radio telescope in South Africa, includes three studies published today in Monthly Notices of the Royal Astronomical Society. Together, these works offer new insights into the universe’s most massive black holes, how they shaped the Universe, and the cosmic architecture they left behind.

Lead author for two of the papers and a researcher at OzGrav and Swinburne, Dr Matt Miles, says the research opens new pathways for understanding the universe that we live in.

“Studying the background lets us tune into the echoes of cosmic events across billions of years,” Dr Miles explained. “It reveals how galaxies, and the universe itself, have evolved over time.”

The MeerKAT Pulsar Timing Array, an international experiment which uses the MeerKAT Radio Telescope in South Africa, one of world’s most sensitive and cutting-edge radio telescopes, observes pulsars and times them to nanosecond precision. Pulsars—rapidly spinning neutron stars—serve as natural clocks, and their steady pulses allow scientists to detect minuscule changes caused by passing gravitational waves. This galactic-scale detector has provided an opportunity to map gravitational waves across the sky, revealing patterns and strengths that challenge previous assumptions. Lead author for one of the studies and a researcher at OzGrav and Monash University, Rowina Nathan comments “it is often assumed that the gravitational wave background will be uniformly distributed across the sky.” Miss Nathan explains “the galactic-sized telescope formed by the MeerKAT pulsar timing array has allowed us to map the structure of this signal with unprecedented precision, which may reveal insights about its source.”

Key findings:

Unprecedented gravitational wave signal
The study uncovered further evidence of gravitational wave signals originating from merging supermassive black holes, capturing a signal stronger than similar global experiments, and in just one-third of the time.

“What we’re seeing hints at a much more dynamic and active universe than we anticipated,” Dr Miles said. “We know supermassive black holes are out there merging, but now we’re starting to ask: where are they, and how many are out there?”

Detailed gravitational wave maps with unexpected hotspots
Using the pulsar timing array, the researchers constructed a highly detailed gravitational wave map, improving upon existing methods. This map revealed an intriguing anomaly – an unexpected hotspot in the signal that suggests a possible directional bias.

“The presence of a hotspot could suggest a distinct gravitational wave source, such as a pair of black holes billions of times the mass of our Sun,” said Miss Nathan. “Looking at the layout and patterns of gravitational waves shows us how our Universe exists today and contains signals from as far back as the Big Bang. There’s more work to do to determine the significance of the hotspot we found, but this an exciting step forward for our field.”

These findings open up exciting questions about the formation of massive black holes and the Universe’s early history. Further monitoring with the MeerKAT array will refine these gravitational wave maps, potentially uncovering new cosmic phenomena. The research also has broad implications, offering data that may aid international scientists in exploring the origins and evolution of supermassive black holes, the formation of galaxy structures, and even hints of early universe events.

With continued work using the MeerKAT array and plans to better understand the pulsar network and gravitational wave signal, researchers aim to refine the map of the gravitational wave background and verify the underlying cosmic structure. “In the future, we aim to understand the origin of the gravitational wave signal emerging from our data sets. By looking for variations in the gravitational waves across the sky, we’re hunting for the fingerprints of the underlying astrophysical processes”, adds Kathrin Grunthal, a researcher from the Max Planck Institute for Radio Astronomy and a co-author of one of the studies.

“By looking for variations in the gravitational wave signal across the sky, we’re hunting for the fingerprints of the astrophysical processes shaping our universe.”

Dr Matthew Miles and researcher Rowina Nathan are available for interviews. For enquiries, please contact ozgrav.comms@swin.edu.au

We are delighted to celebrate two incredible OzGrav members who have been featured in the September issue of Nature Astronomy. OzGrav’s Creative Technologist and Scientific Visualisation Specialist, Carl Knox, created the captivating cover image depicting CSIRO’s ASKAP radio telescope alongside two versions of a mysterious celestial object: a neutron star or a white dwarf. The artwork brings to life the groundbreaking research led by OzGrav Associate Investigator, Dr. Manisha Caleb.

Dr. Caleb’s paper, published in Nature Astronomy in July, reveals the discovery of a slow-spinning neutron star that defies conventional astrophysics. Most neutron stars rotate in mere seconds, but this one takes nearly an hour—a finding that challenges our understanding of these dense celestial objects. Dr. Caleb explained, “It is highly unusual to discover a neutron star candidate emitting radio pulsations in this way. The fact that the signal is repeating at such a leisurely pace is extraordinary.”

Carl’s visualisation accompanies Dr. Caleb’s incredible research and perfectly captures the intrigue and mystery of this unusual celestial phenomenon. Their work together represents the power of combining science and art to deepen public understanding and appreciation of space discoveries.

Congratulations to both Manisha and Carl for their outstanding contributions to astronomy and for representing OzGrav on the international stage!

Read more about the discovery here

As part of National Science Week, the ARC Centre of Excellence (OzGrav) and the Centre for Astrophysics and Supercomputing (CAS) at Swinburne University proudly hosted “A Virtual Tour of Einstein’s Universe”, an inspiring public lecture presented by Professor Matthew Bailes, Director of OzGrav. Held on campus, the event attracted a strong turnout of science enthusiasts of all ages eager to learn about the universe’s greatest mysteries—from gravitational waves to black holes and pulsars.

Hosted by Professor Alan Duffy, the evening began with a warm introduction to Professor Bailes, followed by a fascinating journey through space and time. Professor Bailes explained how Einstein’s theories are shaping our understanding of the cosmos today. The audience was captivated by discussions on cutting-edge science, with a lively Q&A session rounding out the event.

The event also featured our National Science Week Ambassador, Dr Sara Webb, who helped create an engaging and educational experience, fostering an exciting atmosphere for learning and exploration during National Science Week.

In addition to the public lecture, OzGrav’s Outreach Ambassadors hosted interactive workshops, providing hands-on activities for attendees of all ages and fostering an exciting atmosphere for learning and exploration.

This successful event wouldn’t have been possible without the dedication of the OzGrav team and the Swinburne outreach staff. Stay tuned for more exciting events from OzGrav and Swinburne!

For those who missed the event, a recording of the lecture is below and you can also explore the gallery to view photos from the event.

We are delighted to share that the Einstein-First project, a groundbreaking science education initiative, has been awarded the Science Engagement Initiative of the Year at the 2024 WA Premier’s Science Awards. This recognition highlights the exceptional impact Einstein-First has made in transforming the way young students, especially girls, engage with and understand modern science.

Einstein-First began as an outreach effort at the Gravity Discovery Centre and has since evolved into a national program that brings Einstein’s 21st-century science to students aged 7 to 15. The program’s innovative approach disrupts traditional teaching paradigms by using toys, songs, and hands-on activities to make complex scientific concepts accessible and engaging.

The program’s success is evident in its rapid expansion. Launched nationally by Prof. David Blair, Prof. Ju Li, Prof. Susan Scott and Prof. Marjan Zadnik, along with others, Einstein-First has already trained 150 teachers across 55 schools, impacting over 10,000 students, including 3,000 First Nations students in Queensland. The train-the-trainer model has been particularly effective, empowering teachers to bring Einstein’s science into classrooms across the country.

OzGrav has been a proud supporter and collaborator of Einstein-First. This partnership is a testament to our shared commitment to advancing public understanding of modern physics and inspiring the next generation of scientists.

We congratulate the entire Einstein-First team for their outstanding achievement and well-deserved recognition and look forward to continuing our collaboration to further science education and engagement across Australia.

About the Western Australia Premier’s Science Awards

Now in its 23rd year, the Western Australia Premier’s Science Awards celebrate the outstanding scientific research and engagement efforts in the region. The Science Engagement Initiative of the Year category specifically recognises initiatives that have made a significant contribution to raising community awareness, interest, and participation in science.

Check out the announcement here!

Neutron stars are extremely dense objects, second only to black holes. A teaspoon of neutron star matter weighs as much as Mt. Everest. Under such high densities, neutron stars possess exotic physics that cannot be reproduced on Earth.

We have been studying a subgroup of neutron stars, namely pulsars, that release their energies mainly through electromagnetic radiation. But these stars are only a fraction of the total neutron star population in the Milky Way Galaxy. We are missing out on other types of neutron stars that may not produce much electromagnetic radiation.

As a neutron star rotates, any mountains on its surface – even if they are just a few millimetres tall – will create ripples in the four-dimensional fabric of space- time. Such ripples are known as continuous gravitational waves, or continuous waves for short. Compared to the gravitational waves that have been detected, continuous waves are fainter but constant – similar to the humming of a fridge, as opposed to a loud bang.

Observing neutron stars through continuous waves provides us with information that is complementary to what can be learnt from pulsars, so that we can paint a more complete picture of the unknown physics that lies within. However, continuous waves from neutron stars are still undetected. To know whether they are detectable, and what we can learn from them, we need to perform simulations to see if our current and future gravitational wave detectors can detect continuous waves.

In this study, we looked at the capabilities of two detectors: LIGO, the first to detect gravitational waves in 2015; and the Einstein Telescope, a next- generation detector that is expected to be constructed in the 2030s. The first step to detecting continuous waves is to make sure that we are looking at the right place. The current catalogue of neutron stars contains only pulsars that may not emit any continuous waves. To get a full picture of the neutron star population in the Galaxy, we also need neutron stars that emit continuous waves. We simulated the entire neutron star population in the Galaxy, which includes continuous wave-emitting neutron stars. These stars have different energies and release different amounts of electromagnetic and continuous waves.

From this population of neutron stars, we then estimated the continuous waves produced by these stars, and how the two detectors respond to them. Using a technique called Bayesian inference, we performed searches on the faint “hums” amidst all the additional noise from the detectors. Being a next- generation detector, the Einstein Telescope is larger and more sensitive than LIGO, so the weak continuous wave signals can be more easily identified – just like how you can hear fainter sounds when you are in a quieter room.

The factor that determines the amount of continuous waves generated, known as the ellipticity, could be measured by the Einstein Telescope with an error of between 5 and 50% with 5 years of observation. This property of the neutron star cannot be determined by other methods. The limiting factor, we found, is the preciseness of our measurement of a quantity called the braking index. This number determines the fraction of a neutron star’s energy that is released as continuous waves. The ability to measure this number directly affects our measurement of ellipticity.

Our study demonstrated that future detectors, such as the Einstein Telescope, can detect continuous waves. Neutron star properties such as ellipticity, which previously could not be determined, can then be measured through the detected continuous waves. Our work provides a new way to probe the physics of neutron stars, and additional motivation to construct the next generation of gravitational wave detectors.

Reference: “Population Synthesis and Parameter Estimation of Neutron Stars with Continuous Gravitational Waves and Third-Generation Detectors”

Yuhan Hua, Karl Wette, Susan M. Scott, Matthew D. Pitkin.

Published on arXiv.