Australasian Science: Australia's authority on science since 1938

Stars Above, Energy Below

By Stephen Luntz

Outside her research on the birth of the first stars, Rachel Webster is working on the use of geothermal energy in Victoria’s coal fields and running programs to support women in science.

Prof Rachel Webster is a leading figure in Australian astronomy research. However, her latest work sees her seeking clean energy sources beneath our feet.

Webster says she was “always interested in science” and decided at 7 or 8 she would become a physicist. At 17 she went on a science camp. “There was a guy lecturing on cosmology and I thought, ‘Yep, that’s what I will do’,” she says. A degree in pure maths from Monash was followed by a Masters at Sussex University and a doctorate at Cambridge.

Webster’s thesis was on gravitational lensing, the study of distant objects whose light has been focused by the gravity of intervening galaxies so that they appear larger and brighter than they otherwise would. “I have a longstanding interest in using lensing to map the distribution of dark matter,” says Webster, who is now based at the University of Melbourne’s Physics Department. Since light is bent further when a greater mass exists between us and the object being observed, substantial bending can be used as an indication of the presence of mass we cannot otherwise see.

This use for gravitational lensing is in addition to its more common application as a “natural telescope”. “I’ve developed a technique to measure the size of the emission regions of quasars. These are scales of about a millionth of an arc second, so three orders of magnitude smaller than anything else we can see,” she says. This is only possible with the assistance of stars positioned so they can focus the quasar’s light.

Webster’s other specialisation is the Epoch of Reionisation, a period when the first stars were born. “We know it lies at greater than redshift 6,” says Webster, who is using the newly opened Murchison Wide Field Array, a predecessor of the Square Kilometre Array (AS, September 2013, p.15) to detect hydrogen from that time using very low frequency radio waves.

“We are not at all confident we will find it, but we believe the telescope is capable of doing it,” Webster says. “We have 300 hours of observing time booked over the next few months, plus some next year. Each hour produces a terabyte of data, which we have to do something sensible with.”

Webster has been concerned about the implications of climate change for a long time, and is working on geothermal energy as a low carbon power source. “I don’t see this as an area of research, although I have been involved with a couple of research papers,” she says. “I am trying to promote debate on geo­thermal energy, which I see as the most undeveloped clean energy source, and one which Victoria may be able to usefully harness.

“Geothermal energy is available at most places on the planet,” Webster says. “It comes in all sorts of guises. It can be used to heat buildings anywhere.

“Electricity production is easiest around the Ring of Fire. However, we are interested in places where there is elevated heat near enough to the surface to be reached through drilling, which at the moment is 4 km.”

Ironically, this most often occurs under coal deposits, since coal is an excellent insulator and traps heat generated by radioactivity below. To harness this thermal energy, water will be pumped to great depths and return as steam that can power a turbine.

Webster is part of teams exploring the capacity of Victoria’s La Trobe Valley for such activity. “We’ve also done one piece of research to see if it is possible to reduce the amount of brown coal the Loy Yang Power Station burns by preheating water using geothermal energy, and we have a paper saying it is economically feasible.”

While Webster says her specific astronomy research projects have not proven applicable to the search for deep energy, she says: “Being a scientist, one is reasonably quantitative and I would argue strongly that an understanding of physics in particular can be applied to a lot of problems”.

Webster is also a keen science communicator and promoter of women in science. She is leading a program to place telescopes and run astronomy programs in schools in Melbourne’s north-western suburbs. The pilot, at an all-girls school, saw a surge in Year 11 and 12 physics enrolment in the first years after it began.

“Promoting women in science is something I care strongly about,” Webster says. “I’m encouraging women to stay in the scientific professions where they are rarer. It is a bit about role models, a bit about mentoring, a lot about convincing them they are good enough.

“We have had an active ‘women in physics’ program at Melbourne where we go away for weekends. It is a very organic event; we talk about anything that students are interested in, so it varies from year to year.”