July 2011 - Issue #13
Cosmic map maker plots the unseen universe
Story by Julian Cribb
View articles in related topics: Astrophysics
Key points
- One of Australia’s most cited astronomers, best known for determining the precise value of Hubble’s Constant, is the latest star recruit to join Swinburne's astronomy powerhouse
- Swinburne’s agreement with the powerful Keck Observatory in Hawaii will help the dark matter expert probe some of the most baffling aspects of cosmology
For more than three decades Professor Jeremy Mould has been a leader in the quest to discern the true nature of the unseen universe. Having recently joined Swinburne’s Centre for Astrophysics and Supercomputing (CAS), the eminent astrophysicist now has his greatest quarry in plain view.
With colleagues at the ARC Centre of Excellence for All-Sky Astrophysics (CAASTRO) and using the power of the world’s most advanced instruments, the Keck Observatory and the Australian Square Kilometre Array Pathfinder, Professor Mould plans to create a map that will reveal the distribution of enigmatic dark matter and dark energy, whose telltale traces can be glimpsed in the perturbations and rotational speeds of galaxies and star clusters.
At stake is nothing less than the modern cosmological theory of how the universe works. “When we study these galactic movements, we can see there is something very strange and intriguing going on. There are deviations from what cosmology would have us believe,” Professor Mould explains.
Momentous discoveries ahead
Conventional theory holds that dark matter – which appears to account for about 24 per cent of the universe’s energy budget – should be distributed in much the same proportions as the visible universe of stars and galaxies. But if it is distributed differently, then the rules of cosmology and maybe particle physics need to be seriously revisited.
Professor Mould explains how dark matter theory arose. “Astronomers totalled up the starlight emanating from individual spiral galaxies, estimated how much mass was responsible for the starlight and found it was insufficient to cause the rotational velocities they measured for these galaxies. The further from the centre of the galaxy one performs this comparison the worse the discrepancy becomes, until it becomes a factor-of-10 discrepancy at the galactic edges.”
Despite being identified in 1974, dark matter has for nearly four decades defied all scientific attempts to be detected directly, compared to the established method of inferring it from galactic momentum.
Efforts to explain dark matter as consisting of neutrinos or other exotic subatomic particles have not yet borne fruit. Its partner in the dark sector – dark energy – in fact appears not to be due to any of the major forces defined by particle physics as the dominant factors in the universe.
“From the evidence so far, we’re 95 per cent positive that something really odd is going on in the local billion light years. Something cosmological theory alone cannot fully explain. But 95 per cent isn’t good enough for astronomers. We have to be 100 per cent sure,” Professor Mould declares.
He is quietly confident that in the coming years he and his colleagues will gather the necessary evidence. One of the research programs already underway using the Keck Observatory focuses on dwarf galaxies which, inexplicably, appear to have more than their fair share of dark matter.
“Something is going on inside these dwarfs that breaks the rules – but we don’t yet know what. It’s a brilliant opportunity for the upcoming generation of keen young astronomers to be in on what promises to be one of the most momentous discoveries in the history of astrophysics,” he enthuses.
Stellar career
Professor Mould embarked on his own voyage of discovery of the universe when he graduated from the University of Melbourne in 1972 and gained his doctorate at the Australian National University three years later.
He has been director of Mount Stromlo and Siding Spring observatories in Australia and the US National Optical Astronomy Observatory in Tucson, Arizona, as well as principal investigator on the Hubble Space Telescope, and adviser to NASA and the European Southern Observatory.
He is best known for his contribution to determining the precise value of Hubble’s Constant, a key number in astronomy, which in turn has helped define the age of the universe at about 14 billion years.
Among his personal eureka moments was one in the late 1970s when he was able to pin down the relationship between the brightness of galaxies and their rotational velocity – a critical element in the exploration of the dark sector. Another came when he was studying the nearby universe with the Hubble Space Telescope and managed to establish a second indicator of the accelerating universe by reconciling its rate of expansion with the ages of stars in globular clusters.
For much of his research career, Professor Mould admits, he has been “nosing around the dark sector”, determined to lift the veil on its mysteries.
In the course of his work Professor Mould has also served on the scientific steering committee for the giant Keck telescopes in Hawaii. “I helped design it – but I didn’t get to use it,” he ruefully admits of the observatory.
Now, through Swinburne’s unique access agreement with the Keck, he is one of those in the driving seat of astronomy’s most potent instruments, deploying its prodigious powers of resolution to probe one of the enduring questions of cosmology.
Today he ranks in the top 0.5 per cent of astronomers worldwide, based on the citation rate of his scientific papers, joining Professor Warrick Couch and Professor Karl Glazebrook to form a rare triumvirate of ‘Hi-Ci’ (high citation) astrophysics leaders at Swinburne – three out of just 10 in Australia.
CAS director Professor Couch observes: “Jeremy’s arrival strengthens Swinburne’s place as one of the world’s leading astronomical research institutions. In the recent ARC Excellence for Research in Australia assessment, Swinburne was awarded a rating of five in the Astronomical Space Sciences category, recognising outstanding research that is well above world standard.”
On such intellect, leadership and experience, Swinburne is building a launch pad for the next phase in the discovery of our universe.
