University of Sydney PhD student Christopher Hales has won the 2008 Bok Prize.
Aussie astronomer wins prize for his work on a mouse that roars
4 Sep 2008
Every year, the Astronomical Society of Australia—the nation's body of professional astronomers—awards a prize for outstanding research in astronomy by an Honours student at an Australian university. The Bok Prize, as it is called, is named after the late Bart Bok, a past director of Mount Stromlo Observatory.
This year's Bok Prize was awarded to University of Sydney PhD student Christopher Hales, for research that has led to an understanding of a weird celestial object known as The Mouse, which is roaring through interstellar space.
SpaceInfo.com.au recently caught up with Chris to find out more about The Mouse and the work that led to the prize.
Please tell us what your research is about and what it has found.
Massive stars end their lives in style with a cataclysmic explosion known as a supernova, violent enough to be seen around the Universe. These events can result in the formation of a magnetised, ultra-dense neutron star, with a mass more than our Sun but compacted within a radius of only around 13 kilometres (for comparison, our Sun has a radius of around 700 million kilometres!).
Pulsars are a type of neutron star, spinning rapidly and producing pulses of radio emission, much like a lighthouse seems to send out pulses of light as it rotates. Through an outflow of energetic particles, young pulsars can 'inflate' a bubble of gas around them, known as a pulsar wind nebula (PWN). When these pulsars are moving supersonically through the thin gas between stars—the interstellar medium (ISM)—a bow shock can form, similar to the bow shock around a speeding bullet.
The 'Mouse' is a beautiful example of such a bow shock PWN, aptly named because of its apparent compact 'snout,' bulbous 'body' and long 'tail.' My honours project involved determining just how fast the Mouse is moving in order to better understand its history and the gaseous medium through which it is travelling.
'The Mouse' is the aptly chosen name given to the shape of the 'bow shock' produced as the pulsar J1747-2958 roars through the gas of interstellar space at a speed of 305 kilometres per second. Image courtesy of Yusef-Zadeh & Gaensler, 2005.
To do this, I compared radio images of this system obtained with the Very Large Array synthesis radio telescope over a 12-year span. I was able to measure a blistering motion of 305 km/s, which is actually a reasonable speed for such a pulsar.
By analysing its bow shock I was then able to infer the density of the gaseous ISM surrounding the Mouse…in effect using the well-defined geometry of this system to infer the properties of interstellar space 16,000 light-years away.
I was also able to estimate the age of the Mouse's pulsar, as well as conclusively show that this pulsar is not associated with a nearby supernova blast remnant. Finally, by comparing different age estimates for this pulsar, I was able to suggest that it may be evolving into a magnetar, an exotic type of neutron star with a very strong magnetic field.
Why did you choose this problem for investigation?
I've always been fascinated by the cosmos and by science in general, so the choice to turn my research eye towards astrophysics was one of the easiest decisions I ever made. Moving into honours year, I couldn't help but be drawn towards a project involving a pulsar, one of the most fascinating and extreme objects in the Universe.
What challenges did you face in doing this research?
As with any research project, a lot of time and effort has to be devoted to really understanding the theoretical background, your instrumentation, your data, and most importantly your errors. After all, if you don't understand how your experiment could go wrong, then you probably don't understand how it actually works. Trying to constrain a motion for the Mouse pulsar and understand the associated errors was most certainly a challenge, not made easier by the steep learning curve associated with understanding the workings of a synthesis radio telescope. However, it was the anticipation of challenges like these that drew me to science in the first place.
What telescopes and facilities did you use, and did you get help from other astronomers?
I used data obtained from the Very Large Array (VLA), a synthesis radio telescope consisting of twenty-seven, 25-metre-diameter antennae, located in New Mexico (USA). I also obtained data from the Australia Telescope National Facility (ATNF) Pulsar Catalogue. This contains information on all pulsars known, the majority of which were detected with the Parkes Telescope here in Australia. My research for this project was carried out as an honours student in the Institute of Astronomy within The School of Physics at The University of Sydney in 2007.
The Very Large Array (VLA), a synthesis radio telescope consisting of twenty-seven, 25-metre-diameter antennae, located in New Mexico. Image courtesy NRAO.
I carried out the project with two very talented researchers, my supervisor and ARC Federation Fellow, Professor Bryan Gaensler, and my associate supervisor and University of Sydney Research Fellow, Dr Shami Chatterjee. I cannot thank them enough for their help and guidance, and for letting me get a glimpse of how real science should be carried out. I hope this award reflects well on their efforts to educate me in the world of pulsar physics and beyond. I was also helped by having a very supportive partner, who didn't mind the occasional nerdy quip!
What implications arise from this work? Will you or other astronomers be able to use it to study other astrophysical problems?
One of the most interesting problems at the moment is just how magnetars are formed—do they get their extreme magnetic fields from their progenitor stars, or is there some evolutionary link back to neutron stars with lower magnetic fields? Could both of these mechanisms be at play? My honours research will help to increase the small number of systems in which such evolutionary tendencies can be inferred. The result is just one more piece in an intriguing puzzle that has yet to be solved.
What got you interested in astronomy, and why did you decide to take it on as a career?
After completing a degree in Aerospace Engineering from the University of New South Wales, spending a year in the USA at Purdue University to focus on spacecraft engineering, I realised that I was not completely satisfied simply using rules to engineer new solutions. I wanted to go a step deeper and be at the forefront of scientific discovery; to play a role in helping humanity understand more about the Universe we live in. I couldn't think of a more interesting career!
What have been some of the highlights of your astronomical education/work experience so far?
Having only entered into a physics degree in 2006, this is the first project relating to neutron stars that I have completed. However, it isn't my first astrophysical research project. In the second half of 2006, together with supervisor Associate Professor Geraint Lewis, I looked into the gravitational bending of light as it travelled from a very distant galaxy past stars in a much closer galaxy. This can
cause 'microlensing', where the brightness of the background galaxy
is amplified as more light is bent into our line of sight, as if someone
placed a magnifying lens in front of it. By investigating such events, I
found that details about the central regions of the very distant galaxy,
containing a supermassive black hole, could be inferred.
My work at Sydney University, made possible by the warm welcome and encouragement I received from the current Head of School, Associate Professor Anne Green, has been fantastic. Awards like the Bok prize are icing on the cake.
Beyond physics, my engineering work led me to get involved with the BLUEsat microsatellite project at The University of New South Wales, where I am responsible for the design and manufacture of the satellite structure, as well as the attitude control system. This student-managed project, of which I have played a major role in overseeing, has definitely been a highlight of my academic career so far, affording me experiences such as participation in the recent Senate Standing Committee on Economics Inquiry into The Current State of Australia's Space Science and Industry Sector.
What are you working on now?
I recently started a PhD with Bryan Gaensler and former CSIRO Australia Telescope National Facility director, Dr Ray Norris. My work will investigate the evolution, structure and origin of large-scale magnetic fields in the Universe.
Do you plan to continue in astronomical research?
In the medium term I would like to complete my PhD and hopefully continue on to a post-doctoral position. Beyond that, who knows what the future has in store. I'm not one to try and plan out my life, because I think it is often the unexpected things that can deliver the most interesting and fulfilling changes and challenges.
More information:
— University of Sydney, Institute for Astronomy
— Very Large Array
— Astronomical Society of Australia
— The Bok Prize
— Senate Inquiry into Australia's Space Science and Industry Sector
