Research profile of Swinburne astronomer Associate Professor Alan Duffy, Lead Scientist of the Royal Institution of Australia, with published articles on dark matter, dark energy, galaxy formation and cosmology, view at ADS or Google Scholar. He is an experienced public speaker, science communicator and leading expert in space science and astrophysics.
I study the formation of the First Galaxies and the Epoch of Reionisation as part of the DRAGONS team led by Professor Stuart Wyithe. This uses a (SPH) hydrodynamical simulation series Smaug and a larger volume N-body (i.e. dark matter) simulation Tiamat with a new semi-analytic model Meraxes to predict what telescopes will see reionisation.
I am a Chief Investigator in the world's first dark matter detector in the Southern Hemisphere called SABRE based at the bottom of a gold mine at SUPL (Stawell Underground Physics Laboratory) in Victoria, Australia.
From 2017 - 2024 I am an Associate Investigator in the ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO3D) and the ARC Centre of Excellence for Gravitational Wave Discovery (OzGRav).
As a member of two leading surveys on the next-generation Australia Square Kilometre Array Pathfinder telescope I create local universe simulations that can be used to test our galaxy formation and dark matter theories when compared with observations from the WALLABY and DINGO surveys.
This CV contains all my various activities.
My Research Papers
My former student, and now high flying postdoctoral researcher at Leiden University, Dr Camila Correa answered one of the basic questions in galaxy formation in this paper - how does gas get to the galaxy from the larger Universe? The simple answer is, it depends. Essentially the bigger you are the more gas you can pull in, until you get to something the size of our Milky Way, when the `accretion' rate of material infalling then flattens out. This picture is complicated as the hot gas halo surrounding a galaxy is responsible for preventing new material from infalling as it shocks against the hot halo. The amount of the hot halo depends on the type of energetic events within a galaxy, be it exploding stars (supernovae) or accreting black holes (AGN). A beautiful bit of work that will inform theorists and observers for years to come!
One of the challenges in exploring the early universe is that it is so far from us, as we peer billions of light years away to see it as it was all those billion of years ago. That means small faint objects, like dwarf galaxies, that we suspect do the main job of reionising the universe are nearly impossible to measure. It's therefore a challenge to constrain the DRAGONS universe; one way is to wait until little things build into bigger things that you then can see and test those. The other is to constrain the Semi-Analytic Models against the hydro simulations of Smaug. In this astounding exhaustive and thorough review of the two techniques my student Yuxiang Qin explores the connections and learns what to modify in one to mimic the other. Just being on top of one of these techniques would considered impressive in a PhD, to do both is truly exceptional.
The Australian Space Agency review is to be released in a matter of days but do you know what it means for you, your children's future careers or even how much you already use space in your everyday life? Well with the team at The Royal Institution of Australia we put together a package answering all of these issues on Australia's Space Future. I'm really proud of the team's exhaustive efforts and also amazed by the careers of talented female scientists and engineers like Andrea Boyd, Flavia Nardini and Lisa Stojanovski who we were able to feature. In space our future really is unlimited.
It was truly a remarkable privilege to be one of the #CHOOSEMATHS Ambassadors and speak to 400 young girls about the value of maths in their careers. My thanks to AMSI for the opportunity as well as allowing me to hear the fantastic female ambassadors onstage - their stories and range of careers will inspire that audience to know a background in maths is a valuable (and valued!) one for any future job they may strive towards. Also my thanks to IMAX Melbourne for hosting us all, it was a fantastic place to enjoy the #CHOOSEMATHS ambassador's career videos - for more on why I think maths is key to all our futures (and in particular for women) head to the women in education special in The Australian #IWD2018
It's truly a remarkable thing to get to present your research to the Assistant Minister for Science, Jobs and Innovation Zed Seselja alongside fellow scientists in ecology, quantum computing and mining... this is what makes Science Meets Parliament such a unique experience and one I'm proud to have assisted as an executive of Science & Technology Australia.
At the truly epic World Government Summit I was privileged to lead the discussion of Mars settlement by the best and brightest from the UAE Space Agency and make the broader case for space with an international panel. Apart from that I got to hear from Forest Whitaker, Neil DeGrasse Tyson and Michio Kaku all in one day..! The #worldgovsummit is truly an extraordinary meeting of the world’s best minds. Just as exciting will be to see the new businesses and activities that come from this meeting, I certainly aim to work more closely with an international range of impressive people, all with varied backgrounds I could never hope to have met at any other meeting. It was a genuine pleasure to meet and discuss space technologies with the extraordinary young engineers of the Mohammed bin Rashid Space Centre. I have to say the task facing the program director for Mars 2117, Saeed Al GerGawi, are humbling - but he and his team are more than up to the task if this gorgeous VR tour of their Mars City is anything to go by!
My old student Camila Correa continues to revolutionise the basic fundamentals and assumed wisdom of galaxy formation. In particular she thoroughly explored the simple idea that infalling gas will shock against the other gas floating around the galaxy. In this paper, Camila used the EAGLE simulation series to explore the way in which exploding stars (supernovae) or feeding blackholes (AGN) impact that development of the hot halo. Essentially the supernovae ejects gas from the galaxy into nearby space, presenting a bigger target to infalling material, and hence makes the hot halo easier to form. The blackholes on the other are more energetic and eject material from the halo entirely, making it harder to form the hot halo in the first place. Overall, Camila showed that there was a critical halo mass above which the hot halo will form, around a half the size of the Milky Way at the present day.
One of my favourite human beings, colleagues and collaborators - Dr Paul Geil - also came up with one of my favourite paper titles of all time. The work using DRAGONS focusses on the structure of the Epoch of Reionisation. In the first billion years after the Big Bang growing galaxies shone with ionising UV light, lighting up the Universe itself. This light ionised the hydrogen gas lying around the galaxies, creating cavities or bubbles in the intergalactic medium. the exact structure of the bubbles, how many of a given size and their rate of growth, is intimately tied to the nature of dark matter and the physics of galaxy formation. Paul predicted how new telescopes like the Square Kilometre Array can explore these bubbles, and exactly how awesome they will be at constraining all sorts of physics. A huge piece of work that will be years in the testing, so forward looking is its predictions.
OK yes I know citation metrics are not the best way to measure performance. And yes by making the measure of success the target of success we then ruin the value of the measuring metric in, well, measuring (sorry for butchering your Law Goodhardt). But it was still a thrill to see one of my works be cited and used by international colleagues 500 times now. Amazing to think something I have done has been useful to so many great scientists!
In Swinburne's version of the Oscars (yes, just as glamorous, albeit with less acceptance speech tears) we had our best and brightest recognised, and I was truly humbled to see my Science in VR team's efforts counted amongst such top Swinburne staff. SciVR won the VC Award for Community Engagement, which caps off an incredible year for this app. It was also fantastic to be highly commended with my colleagues in the Deans and VC Scholarship Network in the VC's Award for (Higher Education) Teaching Excellence. A great outcome for all and one I was proud to be part of in SciVR and the Scholarship Network. The partying continued well after the event too (sadly I was in bed as I'm now too old for these Oscar shindigs).
One of the oldest questions in the study of Reionisation, the few hundred million years in which almost all of the hydrogen in the Universe was ionised effectively at once, is simple - where does the UV light to ionise the gas come from? One very popular idea is blackholes, or rather the accretion disks around them, where material swirls around the gravitational plughole become incredibly hot and bright in UV / X-ray emission. This fantastic work by Yuxiang Qin used DRAGONS universes to show that there simply isn't enough of these sources, known as AGN or Quasars, to do the job - or at least not if you want to match the number of blackholes that exist today. That's because to be bright, and reionise the universe, they have to feed a lot and in the process grow too large relative to what we see today. This work undoubtedly disappointed some Quasar fans out there, but that's the beauty of science, the facts don't care what you might hope and you have to follow the results to their conclusion.
Where do galaxies form? how big can they be? Do galaxies 'prefer' to lie closer to one another or further apart? And how does all of this change across Cosmic Time? These are just some of the questions Jaehong Park asked within the DRAGONS team in this paper. To explore how galaxies grow near one another, known as clustering, and how they grow within the larger dark matter halos, aka bias, Jaehong analysed countless thousands of simulated galaxies. Compared against one another, at different outputs from the simulated universe of DRAGONS, the overall distributions were robustly analysed with statistical tools that then permitted comparison with images from Hubble. The work is a staggering scale and one I'm sure Jaehong will be proud of for many years to come.
This is a great honour (and also a fun award title!) to be one of Victoria's 2017 Tall Poppies, an award recognising up and coming scientists for their research and efforts to translate this into the public domain. I have to say I felt humbled to be alongside colleagues investigating new solar technologies, cancer treatments and more!
That I got to celebrate it with the two Sarah's in my life (my boss and my wife!) was a real thrill for me.
A lovely piece of work by my student Yuxiang Qin, and amazingly rapid turn around of a paper using the DRAGONS series of supercomputer models. The newly discovered galaxy ZF-Cosmos-20115 had some remarkably strange properties that at first glance seemed to bend the laws of galaxy formation to be so large so soon after the Big Bang. This work instead revealed that the rapid stellar mass gain, and the resulting quiescence thereafter, can be naturally explained by significant mergers of smaller objects that created the large stellar nucleus - but this large central bulge itself then inhibited future star formation. This was then tracked back in time in the DRAGONS universe to reveal that the rapidly growing black holes of the earlier universe could indeed by housed in what then becomes these strange quiescent galaxies at later times.
As radio telescopes become ever larger, and evermore capable, they can see ever further into the Universe. Together with my coauthors, quite literally some of the greatest radio astronomers in the world, we realised that several equations used in radio observations were just too inaccurate (if not wrong!) for the distant universe. This paper is our attempt to give a guidebook and rigorously derived, and checked, equations for this future era of radio observation with the Square Kilometre Array. You can also have fun with the online observation calculator to see what we mean. Fun story I first started doing these calculations with Martin and rest about 6 years ago. Happy to finally see this published!
This is an incredible honour and something I'm delighted to finally announce but after a national application process I've been chosen as the new Lead Scientist of the Royal Institution of Australia, home of Australia's Science Channel.
Australia, and the world, faces significant challenges ahead but it will be more science and technology not less that will see us through. That’s why it’s so critical we continue to explain and share the latest breakthroughs by Australia’s researchers and inspire the next generation into STEM. At Australia’s Science Channel we can ensure the best and most inspiring science stories are fed directly into classrooms around the nation, and further shared around the world.
I hope I live up to the great legacy of the Royal Institution and am able to play a positive role in raising science's profile, and science literacy more generally, in Australia!
This is one of the most fun papers I have ever written (and not just because of the title). The picture astronomers have of the early universe is one of galaxies growing rapidly, turning vast quantities of gas rich clouds into stars in a boom-time of star formation. By using the Smaug simulations of this period I and my DRAGONS colleagues were able to explore this picture. We found that cold gas is indeed consumed rapidly, in just 300 million years irrespective of how stars explode or that gas can cool. However, theres so much material pouring into the galaxies at this time that they simply can't consume it all! A system where demand (gas turing into stars) can't raise to meet supply (of new primary material flowing in) is a recession.
Far from a booming bull-market, the early Universe was a recessionary bear-market and that's why I love this paper...
This is a spectacular study by my Yuxiang Qin, one of my PhD students I am fortunate to co-supervise with Dr Simon Mutch and Prof Stuart Wyithe as part of DRAGONS. In this work Yuxiang compares the growth of dark matter structures in the early universe both with and without the impact of gas physics (in particular the fact that giant clouds of atoms have a pressure that prevents them collapsing unlike dark matter). Most simulations ignore that effect to save computational time. Yuxiang showed that's potentially a disastrous step for first structures where the gas prevents the halo from collapsing and through its gravitational pull can also slow the collapse of dark matter itself meaning simulations that take a computational shortcut can produce early haloes that are far larger than they should otherwise be.
A lovely prediction paper from Chuanwu Liu of the DRAGONS collaboration showing the expected sizes for the most distant galaxies that current (and future) telescopes are trying to observe. The tentative existing detections appear to be well explained by our model of galaxy formation with the effective radius (i.e. the size of the disk of the galaxy) being larger for brighter objects but only with a power law scaling of 0.25! In other words a galaxy ten thousand times more luminous will be a disk galaxy only ten times wider. Finally, we make clear that the successor to the Hubble Space Telescope (the James Webb Space Telescope) will be unlikely to see these tiny disks and instead we will have to wait for ground based extremely large telescopes like the Giant Magellan Telescope (and critically one in which Australia is heavily invested).
The recent discovery by Oesch et al. (2016) of a far-off galaxy seen just 400 million years after the Big Bang but already having accumulated a billion Sun's worth of stars was considered a bizarre object. Yet the simulated DRAGONS universe apparently contains several analogues as shown in this beautiful work by my colleague Dr Simon Mutch. We show that such a monstrously oversized baby galaxy is possible if it grows rapidly but consistently throughout time and not as a result of cannibalising neighbouring objects through galaxy mergers as is oft suspected.
An unusual opportunity came up to speak at the International Mining and Resources Conference housed at the Melbourne Convention and Exhibition Centre to explore the possibilities of spin off tech from our underground dark matter searches. I focussed on the science of SABRE, the possibilities of an X-ray like scan for gold in the mine around using Muon Tomography and other underground science such as understanding how life grows without radiation / astrobiology. Finally I discussed the possible future for mining, in space! Key technologies such as automation and refinement have been deployed by the giants in the resource extraction sector and could find a home for their advanced technologies in the final frontier.
A key goal of the DRAGONS investigation was to predict how growing galaxies in the early universe would ionise the neutral hydrogen around them. This is the long-sought after signal of Reionisation (also known as Cosmic Dawn) when the Universe was filled with light, lifting this dark opaque fog. It is the target for telescopes like the Square Kilometre Array to characterise that early universe when ionised bubbles of gas around the galaxies resembles a swiss cheese model. This beautiful work by Dr Paul Geil calculated how our simulated galaxies would impact that material around them finding that the galaxy formation that resulted in the biggest impact was the nature of how stars exploded. This both ionised gas around it but more importantly limited how new stars could form and hence limit the amount of ionising radiation and therefore the size and number of the ionised bubbles. This is however not a unique signature and instead even when we find the swiss cheese universe we have a lot of work ahead to tease out its lessons. Depressing but beautifully analysed science by Paul.
A mammoth effort by my long-time collaborator Dr Simon Mutch explaining the semi-analytic model Meraxes that `paints' the galaxies onto the background dark matter structures formed in the huge simulated DRAGONS universe. This work has so many critical lessons on key physics that grows a galaxy that matches what we see in the distant universe (and hence seeing those objects as they were long ago when the light first left them). Perhaps the key is that the fraction of energetic light that can escape forming galaxies (and hence ionise the neutral hydrogen atoms in the vast distances between them) has to increase towards earlier times. Somehow galaxies trap evermore of this radiation as they grow up. A mystery that we will hopefully solve in this series of works!
The first paper by Chuanwu Liu in his PhD with DRAGONS showed that we can explain observations of distant galaxies glowing in ultraviolet (UV) light. This light is responsible for ionising the neutral hydrogen between the galaxies, ending the Cosmic Dark Ages in a process known as Reionisation. Chuanwu's work showed that our simulated galaxies can recreate the current observations, but that we can then predict what future observations may see as our simulations form much smaller objects at this time than even Hubble can find. The main finding was that dwarf galaxies are responsible for providing most of the ionising radiation that lights up the universe; in agreement with my entirely complimentary and independent technique in Duffy et al. (2014b). Promising start to your academic career Chuanwu with such a careful and expansive analysis on this hot topic!
The first paper in the DRAGONS series, by my long time collaborator Dr Greg Poole, explaining the enormous dark matter simulation Tiamat that underlines the entire project. This is an epic work detailing the challenges involved in correctly identifying dark matter structures within which galaxies are expected to form. This is particularly challenging at early times in the universe's history when so many dark matter haloes were colliding and merging, causing a nightmare for basic book-keeping or cataloguing of such messy objects. Beautiful work and one that sets the stage for the rest of the DRAGONS papers!
The first paper by Paul Angel for his PhD as part of DRAGONS and it's enormous. A careful phenomenological study and characterisation of the structure of dark matter haloes in the early universe. In particular Paul focussed on the concentration of the dark matter haloes as measured by fitting the halo with the NFW and Einasto profiles. At the current age of the universe works such as Duffy et al. (2008) show small mass haloes are typical denser (that is more concentrated) that more massive ones. This is because smaller objects form earlier than large objects in our hierarchical universe, earlier times in an expanding universe implies that it was overall smaller and hence denser as are then the objects that form. Paul discovered that the universe in DRAGONS is so young that essentially everything is forming at nearly the same time and hence density so the concentration-mass relation is flat!
TAO is an outrageously ambitious project spearheaded by Swinburne's Prof Darren Croton to bridge the gap between observations of our universe and those we simulate (such as the ones I create). Ideally astronomers log onto TAO and select their favourite telescope and strategy for viewing (stare for a long time at a small region, or briefly over a wide path of sky, the former lets you see fainter objects while the latter gives you only the brightest ones). Then you get an output that is identical in format to the one you took with that telescope in reality (including all known issues with signal to noise and interference etc). This makes the comparison between what we predict and observe as close as possible and hence maximise the lessons we can learn from seeing out into the universe.
DRAGONS is out! Our first six collaboration papers are on the arXiv and submitted to the journals. Can’t describe what a relief this is for myself and the team..! Led by U.Melb’s Professor Stuart Wyithe it's been a few hard years of science, simulating the first galaxies after the Big Bang and trying to figure out what these look like from telescopes on Earth, 13 billion years later (and 40 billion light years distant) but finally the results are in and they’re amazing.
I’m CI of the dark matter detector SABRE at the Stawell Underground Physics Laboratory and can proudly announce that we've been funded by the ARC! Australia will now join an international search for the nature of dark matter as the first site in the Southern Hemisphere.
My student's third paper of a stunning 3-part series on the growth of dark matter structures. In this paper Camila finally demonstrated the long studied concentration of dark matter haloes was tied to the growth history of that halo and hence, through her other works, the basic cosmology of the universe. Reference: Correa, Wyithe, Schaye and Duffy 2015 MNRAS 452, 1217C