How did the Universe light up – filling a billion years of cosmic history: 2011 Malcolm McIntosh Prize for Physical Scientist of the Year

Stuart Wyithe

The Universe was born in a hot Big Bang. But after 300,000 years of expansion it became a cold dark place—no galaxies, no stars, no light. A billion years later nuclear fusion lit up the Universe as hydrogen atoms clumped to form stars and galaxies.

We can still detect the heat of the Big Bang. And our best telescopes can see the light of the early galaxies. But how did the first stars and galaxies form? What triggered the cosmic dawn? What happened during the Universe’s billion-year Dark Age?

This is one of the great unknown eras of cosmic history—particularly because there is no light nor other forms of high energy radiation to analyse. Stuart Wyithe’s theories may lead to some answers.

The ideas that this young theoretical physicist is generating on pen, paper and desktop computer will guide the questions to be asked by a new multi-billion-dollar generation of telescopes including the Square Kilometre Array, the James Webb Space Telescope, and the Giant Magellan Telescope.

For his work on the physics of the formation of the Universe, Professor Stuart Wyithe receives this year’s Malcolm McIntosh Prize for Physical Scientist of the Year.

“Stuart Wyithe is the best young scientist with whom I have ever worked in almost 35 years on the faculties of Harvard and Princeton, bar none,” says Professor Edwin Turner of the Princeton University Observatory, “and he is by far the most productive and prolific. He is also the most important and influential theoretical astrophysicist in Australia and among the top 10 or so in the world in my judgment.”

Stuart Wyithe became interested in astronomy when he was young. He grew up in the Blue Mountains where, away from the bright lights of Sydney, the night sky had meaning. At secondary school, he was involved in an astronomy club run by a keen teacher. They used to go camping on the western plains to observe the heavens. (Closer to home, he also became an inveterate rock climber.)

He describes his introduction to academic life as ‘chequered’—moving to Sydney, enrolling in chemical engineering, and then quitting after two years to go travelling. When he returned, it was to finish an honours degree in physics at the University of Melbourne. By this time, he knew what he wanted to do and immediately enrolled in a PhD in astrophysics.

After his first year, Stuart took advantage of a Visiting Student Research Collaborator program to go to Princeton, initially for a semester. That was the last Australia saw of him for several years. He completed his doctorate at Princeton, and then he moved on to Harvard University as a NASA Hubble Fellow, not entirely without ulterior motive. “There was a woman involved, of course,” Stuart says. “She is now my wife.” She’s also a leading young researcher at the Walter and Eliza Hall Institute of Medical Research.

The time in America was very productive. “[Stuart and I] are co-authors of 15 papers in the refereed literature,” says Edwin Turner, “of which 11 were submitted during his graduate school years. He is deservedly first author of all but one of these publications, and carried out the work for the majority of them during his two years in Princeton. It is clear that he is an exceptionally energetic and efficient worker. The quality of his work is no less impressive.”

In fact, in the 14 years since he started his PhD, Stuart has published more than 100 papers, five of which appeared in the prestigious British journal Nature, and for the vast majority of which he has been the lead author.

He was also once one of Australia’s top rock climbers, although, with a young family, he has curtailed this activity somewhat. At one stage some years ago, he held the dual distinction of having made the climb rated most difficult by any Australian and also the most difficult climb ever made by anyone within Australia.

Initially Wyithe worked on gravitational microlensing, a technique used to gain information on distant stars and on planets outside the solar system by observing the bending of light as it passes through a gravitational field. Nearby stars, for instance, bend the light of more distant stars as it passes in front of them.

But more recently Stuart’s work has focused on the evolution of the structure of the Universe. “Astronomy is all about trying to understand how the Universe came to look the way it does, as well as how it works. What’s not understood is how the galaxies themselves formed. This is inexorably linked with the transition from a Universe of cold, uncharged, atomic hydrogen to being ionised and hot. This ‘Epoch of Reionisation’ is the last non-understood event in the history of the Universe.”

“The obvious candidate for the energy that drove this process is the formation of stars, and that is where most attention has been focused.” Another possible source is the formation of supermassive black holes. And it is in these two possibilities that Stuart has been most interested.

“The reason that Wyithe’s work has had so much impact,” says Professor Matthew Colless, Director of the Australian Astronomical Observatory, “is that not only does it elucidate a fundamentally important epoch in cosmic evolution, but it has also focused on making explicit, detailed and testable predictions for the large-scale structures that should be observed. These predictions strongly suggest that there are rich observational signatures of the Epoch of Reionisation just beyond the limit of current facilities.”

The next generation of powerful astronomical instruments either planned or under construction—the Square Kilometre Array, the James Webb Space Telescope, the Giant Magellan Telescope, and Australia’s own Murchison Widefield Array and Skymapper—is designed to plug this information gap.

“The study of the cosmic dawn is deemed to be of such importance that the top recommendation of the 2000 decadal survey in astronomy and astrophysics in the US, which I co-chaired, was [to build] a successor to the Hubble Space Telescope to address this problem,” says Professor Christopher McKee of the University of California, Berkeley.

“Furthermore, that committee also recommended that the US participate in initial work on a very large radio telescope, the Square Kilometre Array (SKA), which would be able to observe the universe in this epoch.”

Australia and South Africa are competing to host the SKA, a giant radio telescope that will cost some two billion dollars to construct.

Stuart Wyithe now chairs the science committee for the Murchison Widefield Array, a revolutionary electronic telescope being constructed by a US-Australian-Indian consortium in Western Australia. It will test some of the ideas to be incorporated into the SKA.

“In my view,” says Professor McKee, “by illuminating our origins, Dr Wyithe’s work benefits all mankind. On a far more practical level, if his contributions to the proposal to build the SKA in Australia are successful, he will certainly have benefited his nation.”

Qualifications

2003	PhD (Astrophysics), The University of Melbourne
1997	Bachelor of Science (Honours), The University of Melbourne