Dark matter in colliding galaxy clusters, travelling back to the cosmic dawn, enabling ‘impossible’ research, and more

Astronomical Society of Australia (ASA), Media releases

National recognition for astronomers from Perth, Canberra, and Melbourne

  • How dark matter behaves in colliding galaxy clusters, explained by UWA/ICRAR student William McDonald
  • Why the Universe’s earliest stars are so elusive, by Dr Piyush Sharda of ANU (now working at Leiden Observatory, the Netherlands)
  • A sharper focus on when the Universe lit up, by Dr Nichole Barry of Curtin University/ICRAR
  • The chemistry of starlight helps explain our galaxy’s evolution, says Dr Sven Buder of ANU
  • A mission to study 6 million galaxies in 5 years, by A/Prof. Michelle Cluver of Swinburne University of Technology
  • Software that enables ‘impossible’ research, by Dr Manodeep Sinha of Swinburne University of Technology.

The Astronomical Society of Australia (ASA) will honour the 6 at its Annual Scientific Meeting at the Macquarie University Wallumattagal Campus in Sydney 3-7 July 2023.

“The research recognised in the awards goes to the heart of some of the biggest questions in astronomy today – such as the nature of dark matter and the evolution of the earliest stars and galaxies – vastly increasing our understanding of the Universe,” says ASA President Professor John Lattanzio.

For interviews, email Bill Condie at Science in Public at bill@scienceinpublic.com.au

How dark matter behaves in colliding galaxy clusters

William McDonald, University of Western Australia/ICRAR, winner of the Astronomical Society of Australia’s Bok Prize 2023 for outstanding research by an honours student or eligible masters student

Dark matter is one of the great mysteries of astronomy. It is thought to account for 85 per cent of all the matter in the Universe, but we can’t see it. We know it must be there, however, because of how galaxies behave.

William McDonald’s master’s thesis expands our understanding of the dynamics of dark matter by modelling the large-scale separation of dark matter and gas that occurs when clusters of galaxies collide.

His highly original research simulated numerous collisions of galaxy clusters from which the dark matter-gas separation was measured using a novel and well-defined method.

This work delivered a new model that predicts the separation of gas and dark matter we can expect from galaxy cluster collisions when we know their orbital parameters and mass ratios.

In the process he also confirmed that the dynamics of the iconic Bullet Cluster – an ongoing violent merger of two massive galaxy clusters, which serves as evidence for the nature of dark matter – are consistent with our standard model of how the Universe works.

Why the Universe’s earliest stars are so elusive

Dr Piyush Sharda, ANU (now the Oort Fellow at Leiden Observatory, the Netherlands), winner of the Astronomical Society of Australia’s Charlene Heisler Prize 2023 for the most outstanding PhD thesis

Piyush’s thesis explores the earliest stars in the Universe. With no metals in the early Universe to help them cool, these ancient stars formed from gases at temperatures 100 times hotter than modern star-forming clouds, with the result that most were massive.

Giant stars use up their hydrogen fuel quickly, resulting in short lifetimes, which explains why none have survived to the present day.

But Piyush wanted to explain the mystery of what happened to stars further from the centre which, theoretically, should have fragmented to smaller stars that could live longer.

His simulations showed that a magnetic field in the discs around first stars could prevent this fragmentation and put the brakes on small star formation.

Piyush also looked at the giant primordial stars to chart the role of metal content in the evolution to the smaller mass of modern stars. His work on the metal content in galactic disks has resulted in a completely new theoretical model embracing for the first time star formation, gas and metal flows, metal diffusion, and the effects of galactic winds.

A sharper focus on when the Universe lit up

Dr Nichole Barry, Curtin University/ICRAR, joint winner of the Astronomical Society of Australia’s Louise Webster Prize 2023 for outstanding research by a scientist early in their post-doctoral career

Nichole’s research led to a 10-fold improvement on the analysis of data gathered by the Murchison Widefield Array (MWA), helping us close in on a signal that has been travelling across the Universe for 12 billion years – from the time the very first stars were born.

Her achievements pave the way for a much greater understanding of the Epoch of Reionisation when the Universe lit up again when its neutral cosmic soup was transformed into the first stars.

The MWA is designed to detect electromagnetic radiation emitted by neutral hydrogen – the predominant gas at the time – but those signals are extremely faint, as if we were measuring a light bulb on Pluto.

Nichole and her colleagues developed new techniques to refine analysis and exclude noise, including ultra-faint interference generated by radio broadcasts on Earth.

This new precision helps us to come closer to dating the beginning of the Epoch of Reionisation.

The chemistry of starlight helps explain our galaxy’s evolution

Dr Sven Buder, ANU, joint winner of the Astronomical Society of Australia’s Louise Webster Prize 2023 for outstanding research by a scientist early in their post-doctoral career

Twenty years ago, we had observed the chemical composition of fewer than 40,000 stars. Galactic archaeologist Dr Sven Buder, is changing that.

His research in the GALAH survey has observed more than 600,000 stars so far with Australia’s largest optical telescope, revealing previously unknown details about the history of our galaxy. GALAH or the GALactic Archaeology with HERMES survey program uses the HERMES instrument with the Anglo-Australian Telescope, which provides simultaneous spectra for 400 stars at a time.

“Galactic archaeology” might evoke a mix of Star Wars and Indiana Jones but in practice Dr Buder works with huge amounts of data and high-tech computers. The data come directly from the light of stars, by splitting it across the wavelengths like a rainbow. And it is revealing all kinds of new information.

“Although it is our home galaxy, we actually know very little about the history of the Milky Way,” says Dr Buder.

One leading theory, supported by his research, is that the Milky Way is composed of several smaller galaxies that collided billions of years ago. He is trying to find rare survivors of massive collisions of galaxies. These stars look the same in pictures, but completely different chemically and Dr Buder’s data will help to find more.

A mission to study 6 million galaxies in 5 years

A/Prof. Michelle Cluver, Swinburne University of Technology, winner of the Anne Green Prize 2023 for a significant advance or accomplishment by a mid-career scientist

Michelle’s work with large surveys such as WISE and 4MOST provides the global astronomical community with high-quality datasets to apply to their own research questions.

She now co-leads an international team of 70 people for the upcoming 4MOST Hemisphere Survey, which will study 6 million galaxies over 5 years to glean details of their composition and to determine their distance from Earth.

This work will be a key to interpreting a host of observations of galaxies made by other astronomy platforms as well as mapping cosmological mass and motion to measure the growth of structure and to test gravity over the largest possible scales.

Her expertise in the use of WISE space telescope mid-infrared imaging, in combination with optical and radio observations, to study galaxy evolution is virtually unique in Australia.

The value of this expertise is clearly reflected in the diversity of science evident in her publication record. Michelle’s work has led to best practices for the use of WISE mid-infrared photometry for large area surveys, and she is noted for her community engagement and leadership.

Software that enables ‘impossible’ research

Dr Manodeep Sinha, Swinburne University of Technology, winner of the Emerging Leaders in Astronomy Software Development Prize – for outstanding contribution to the development of open-source astronomical software by an early career researcher

Manodeep’s CORRFUNC software harnesses one of the most useful statistical tools for astronomers, enabling research that would otherwise be impossible.

His work addresses the widely used correlation function, which measures whether the spatial distribution of objects is clustered or is simply randomly distributed. It is vital for quantifying the spatial distribution of galaxies but computing the function can be slow, making some research projects computationally impossible.

The open source Corrfunc was designed to solve this problem, providing extremely fast computation of correlation functions in an easy-to-use multiplatform package.

The judges were impressed by Manodeep’s deep understanding and application of how to make his code more efficient, reducing time- and energy-consuming computational requirements. People around the world are now choosing Corrfunc as the correlation function code of choice.

Bok Prize – highly commended     

Hank Hua (ANU) Neutron Star Physics from Gravitational Waves with Third Generation Detectors

Ashna Gulati (University of Sydney) Exploring Classical Novae with ASKAP

Charlene Heisler Prize – highly commended

Isobel Romero-Shaw (University of Cambridge, UK) Eccentricity in Gravitational-wave Transients – measurements and implications