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The sound of gravitational waves
Scientists around the world are so ecstatic at hearing the sound of two black holes colliding they begin to chirp.
One had the mass of 36 suns, the other the mass of 29. These remnants of huge collapsed stars smashed together in a cataclysmic event forming a single 62-solar-mass black hole. The remaining
three solar masses were dispersed throughout the universe at the speed of light in the form of gravitational waves, wobbling the very fabric of space-time.
And about 1.3 billion years after the event, these waves passed Earth, zipping by in just two-tenths of a second.
Their detection on September 14 by the Laser Interferometer Gravitational-wave Observatory in the US has opened up a completely new window on the universe.
Until now we have only been able to look at the universe with our eyes – through the electromagnetic spectrum. Gravitational waves are a completely new spectrum by which we can observe our place in the cosmos.
"It's like being able to hear the universe for the first time," Professor David McClelland told Fairfax Media.
Professor McClelland is the director of the centre for gravitational physics at the Australian National University. He also leads the Australian LIGO consortium, part of a global enterprise involving more than 1200 scientists in 15 countries.
If it hadn't been for Albert Einstein's theory of general relativity and the dedicated work of engineers and scientists that made LIGO a reality, we would never have witnessed this event.
And Australian scientists have played a critical role.
The machine that detected the gravitational waves is a very sensitive laser, called an interferometer. "The interferometers are four-kilometre-long systems using light to sense the separation between points," Professor McClelland said.
As the gravitational waves passed this detector they stretched the lasers by an infinitesimally small amount – 10,000 times shorter than the width of a proton. The lasers have to be very carefully calibrated with their reflecting mirrors as to be able to detect this shift.
"The ANU developed a system which brings the mirrors in the interferometer into 'lock'," Professor McClelland said.
"The University of Adelaide role has been to [develop] a correction system to adjust for mirror distortions. And UWA's expertise [was used] to ensure we avoid [mirror] instabilities."
Professor McClelland said: "These contributions give the Australian consortium a stakeholder position in the LIGO project."
Researchers at these three universities, alongside others at Monash University, Melbourne University and Charles Sturt University, were also involved in analysing data coming from the LIGO project.
CSIRO was specifically contracted to polish and coat the laser mirrors at LIGO.
"At the start of the century, CSIRO was recognised as one of only two places in the world that could calibrate the mirrors to the required accuracy," Professor McClelland said.
"The CSIRO Centre for Precision Optics has coated mirrors for the advanced LIGO project and, as I understand it, their coatings are the best that are in that device."
The coatings are among the most uniform and highly precise ever made. This precision ensures that LIGO's laser remains clean and stable as it travels through the detectors.
Details of the discovery and Australia's role were announced in Canberra on Friday.
Nobel laureate and ANU vice-chancellor Brian Schmidt said it was "one of the great, exciting days of my life".
"A fundamental discovery about the universe only happens every couple of decades," Professor Schmidt said.
Alan Finkel, Australia's Chief Scientist, said that as a physics enthusiast you "dream of days like this". He said he expected it would be the "most significant announcement in cosmology in my lifetime".
A hundred years in the making, what is amazing is how quickly gravitational waves were detected.
"We are only at one-third of the design sensitivity of the LIGO project," Professor McClelland said. "In September we reached this stage and settled the instruments down and decided to initiate what is called an 'observing run' for three months to see if we might make a discovery.
Data revealing the colliding black holes emerged within a week.
Eric Thrane at Monash University said that the LIGO team has only analysed the first 16 days of data from this "observing run".
"It takes a village of scientists to make this all work," Dr Thrane said. He and his team at Monash worked on the theoretical designs of LIGO to ensure background 'noise' was controlled and has worked on analysing the data.
So have there been any more encouraging signals in the data?
"I can't comment," Dr Thrane told Fairfax Media.
Given that the first gravitational waves were detected within days of the LIGO project running, Professor McClelland says it is "definitely the case" that we are likely to pick up many more examples.
"Our expectation is that once we are at full sensitivity in two years or so we will be seeing these sorts of signals monthly or weekly.
"It will allow us to witness other events, such as neutron stars colliding or a supernova exploding. It will be a very rich field of discovery."
So is it fair to say that this has opened up a new field in astronomy?
"It's like when Galileo first turned a telescope to the sky. We've never stopped looking at the sky – and now we've started listening to the universe and we'll never stop listening."
"This event will be remembered for a thousand years. It will go down in history as one of the most important measurements in physics yet done."
Susan Scott at the ANU said: "This is just the beginning. We will now explore the universe using this new window: the gravitational wave spectrum."