Putting Einstein to the ultimate test

CSIRO’s Parkes telescope records pulsar signals to try to detect gravitational waves. Credit: David McClenaghan / CSIRO

Einstein’s general theory of relativity predicts them, and they could be scattered throughout the Universe. But so far, gravitational waves— ‘ripples’ in the fabric of space and time—have never been detected. Several Australian teams of astronomers are trying to catch the first signs of one.

Using CSIRO’s Parkes radio telescope, some of these astronomers are hunting gravitational waves by studying signals coming from pulsars— the collapsed cores of exploded stars. Spinning at up to hundreds of times per second, pulsars emit highly regular radio pulses that appear to flash on and off like a lighthouse. And that’s the key to detection.

“If a gravitational wave sweeps through Earth, the pulsar signals detected at our telescope will arrive later or earlier than we would expect them,” says George Hobbs of the CSIRO’s Astronomy and Space Science, and a member of the Parkes Pulsar Timing Array project. Gravitational waves could come from pairs of black holes circling each other. Others could be lingering from a time shortly after the Big Bang.

“Parkes’ ability to see the southern sky is ideal for this project and may lead to the first detection of gravitational waves,” says George. “And when the Square Kilometre Array is built, it will be the perfect telescope for studying the waves in detail.”

The hunt for invisible ripples

Meanwhile, at the Australian International Gravitational Research Centre at Gingin in Western Australia, 65 kilometres north of Perth, David Blair from the University of Western Australia and his team have been exploring techniques of using lasers to detect gravitational waves directly .

Gingin is also the favoured site for one of the most sensitive machines searching for gravitational waves, a Laser Interferometer Gravitational-Wave Observatory (LIGO) detector. Two of these detectors have already been established in the US. Late in 2010, the US National Science Foundation (NSF) offered to provide Australia with its own $140-million LIGO machine—as long as Australia can find a further $140 million to build a facility to house it.

Locating a LIGO detector in the Southern Hemisphere would allow the origin of any gravitational waves to be pinpointed much more accurately. Other types of telescopes could then be trained on the spot, enabling different sorts of observations to be made efficiently.

It would also bring huge advantages to Australia, says Jesper Munch of the University of Adelaide, chair of a consortium of five universities set up to advance the proposal. “LIGO-Australia would put this country at the forefront of the relevant technology.”

In fact, Australian technology is already contributing to the LIGO project. The US LIGO detectors are being upgraded to be ten times more sensitive, and the Australian Consortium for Interferometric Gravitational Wave Astronomy is part of that effort. Researchers at the Australian National University (ANU) in Canberra, and at Adelaide University, are in the middle of a four-year project to produce optical components that will stabilise the LIGO laser system.

“Einstein predicted them, but thought we’d never be able to detect them,” says David McClelland, Director of the ANU’s Centre for Gravitational Physics. “Now, we’re on the cusp of the first direct observation of gravitational waves.”

CSIRO Astronomy and Space Science
Dr George Hobbs, Tel: +61 (2) 9372 4652, George.Hobbs@csiro.au, www.atnf.csiro.au/people/George.Hobbs

ANU Centre for Gravitational Physics, Canberra
Professor David McClelland, Tel: +61 (2) 6125 9888, David.McClelland@anu.edu.au, cgp.anu.edu.au/