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.
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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.
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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.
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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.
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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!
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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!
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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...
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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.
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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).
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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.
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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.
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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.
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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!
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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!
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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!
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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!
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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.
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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.
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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.
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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
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