Sydney astronomy student wins coveted Bok Prize

20 May 2013

University of Sydney PhD student Benjamin Pope has been announced winner of the prestigious 2013 Bok Prize: the highest award of the Astronomical Society of Australia for research conducted by an Honours student.

Ben Pope, Winner of the coveted Bok Prize 2013 for the Best Honours Thesis in astronomy
Ben Pope, Winner of the coveted Bok Prize 2013 for the Best Honours Thesis in astronomy

Mr Pope's citation from the Astronomical Society particularly singled out the important potential for new discovery from the innovative methods, entitled "Dancing in the Dark: Kernel Phase Interferometry of Ultracool Dwarfs". This research, now published in the Astrophysical Journal, delivered the first scientific results with a new image analysis technique with the potential to breathe new life into high resolution astronomical imaging.

In the announcement, the committee noted that "the nominations received for the 2013 Bok Prize were of an excellent standard and the judging panel were highly impressed with Mr Pope's thesis, particularly the new discovery aspect of your work and the development of new methodologies applied to archival data."

Interestingly, this was also a case of finding gold in the astronomy equivalent of a filing cabinet in the attic. "The Hubble Space Telescope has been a truly remarkable observatory, but despite the extreme competition to use it, a lot of the images taken with it have never been analysed to their fullest potential" explained Mr Pope.

"The data I used for my research was mostly taken around 2005 while I was in Year 9 , and it had been sitting on a public archive since then. This data had previously been studied by simple visual inspection, but contained a hidden trove of discoveries accessible only after advanced computer processing. The thing that made all the difference for us was being able to apply the very latest leading-edge image analysis technique called kernel phase interferometry. I was fortunate enough to learn about this straight from its inventor, Dr Frantz Martinache, on a visit to Hawai'i last year. Together we made the first new discoveries with this powerful new approach," said Mr Pope.

It turns out that despite all the effort and expense, even the multi-billion dollar Hubble Space Telescope does not yield absolutely perfect vision.

The mirrors, lenses and other components that comprise the telescope all bend and warp by tiny amounts as the observatory orbits in space, enough to create subtle shifts in the image that are easy to confuse with real signals from the star being studied. The key breakthrough came with the realization that the structure in the image could be mathematically divided into two classes: firstly those which could arise from errors in the mirror, and critically, a second class which could not.

"In essence, we divide the image into two parts", explains Dr Martinache, "the first can be corrupted by optical problems, and we discard this. kernel phase interferometry can then focus exclusively on information in the image which is essentially immune to the noise. It is like a noise-cancelling headset on an aeroplane: you flick off the noise and you can suddenly detect all these faint signals nobody else could find."

Mr Pope's research unleashed this powerful method in the hunt for companions to the intriguing objects known as brown dwarfs which occupy the no-man's-land in mass between gas giant planets like Jupiter, and the smallest, dimmest stars.

"Brown dwarfs are like a missing link between stars and planets, and by studying them we learn more about how the great diversity of star systems in the universe came to be formed." said Mr Pope.

"Although they are incredibly faint, so we never see them except with large telescopes, they are actually very common. Most importantly, nobody is quite sure how they can be formed, and they present a tricky challenge to just about all theories for how matter collapses to form compact bodies like stars and planets. Some say they form like large planets around more massive stars, and are then ejected; other models can have brown dwarfs forming by themselves like stars. In particular, one of the key tests is to find how often brown dwarfs are found in pairs.

This binary fraction is quite high for stars - the in joke among astronomers is that 'three in every two stars is a binary.

"What my work here has shown is that it is in fact also higher than previously thought for brown dwarfs too. This high binary fraction favours theories where brown dwarf systems form like scaled-down star systems," said Mr Pope.

"You can't help but feel a little poignancy for brown dwarfs.", concludes Professor Peter Tuthill, Mr Pope's research supervisor at the University of Sydney, "Failed stars out in the cold reaches of the Galaxy, never to see a sunrise and doomed to slowly freeze as generations of stars around them are born and die. I guess Ben's work gives the poets in us a little solace, in that more of them than we expected are in a stately orbital dance with a partner that will still be going when our own sun has lived its entire life and is but a memory."

Mr Pope's award marks a Hat-Trick for the Sydney Institute for Astronomy at the University of Sydney in winning this prestigious national prize three years in a row with past winners Alison Hammond (2012) and Barnaby Norris (2011).

The paper "Dancing in the Dark: New Brown Dwarf Binaries from Kernel Phase Interferometry", Pope, Martinache and Tuthill, ApJ, 2013 is now published in the Astrophysics Journal.

Contact: Tom Gordon

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