A decade ago, our view of the universe changed completely. And this WA scientist was there for it

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It’s not often someone gets a front-row seat to a history-making event that forever changes our understanding of the universe, but for Australian academic Dr Carl Blair, it was the ultimate case of being in the right place at the right time.

A decade ago, Blair, from the University of Western Australia’s school of physics, mathematics and computing, was in the thick of his PhD studies when he was called out to the Laser Interferometer Gravitational-Wave Observatory – or, LIGO – in the United States.

Dr Carl Blair, from UWA’s School of Physics, Mathematics and Computing and director of the Gingin High Optical Power facility.

The observatory, comprising two sites, uses lasers fired at mirrors spaced kilometres apart to measure miniscule fluctuations that signal passing gravitational waves – ripples in the fabric of space-time caused by extremely energetic cosmic events.

But there was a problem: because the detectors were so sensitive, the mere act of using high-powered optical lasers caused the mirrors to vibrate. Not much, but enough to throw a spanner in the works. That’s where Blair came in.

“I went over there to help fix this problem that I’d been studying as part of my PhD,” he said.

“If you take a microphone and put it too close to a speaker, and you get a squeal coming out of the speaker, that’s closing a feedback loop where the vibration from the speaker excites a signal in the microphone that makes a bigger vibration in the speaker, and that’s the instability.

“So it’s the same sort of problem as that, and we need to somehow break that loop that’s making the instability.”

Blair had just finished fine-tuning a fix when, unbeknown to anyone else on Earth, on September 14, 2015, the ripple from a catastrophic collision of two black holes 1.3 billion years ago passed by and left a clear signal in the observatory’s data.

“The day before the detection happened – local time in Louisiana about 4am – I was actually in the detector until about 2am the night before,” Blair said.

“And so when I woke up the next morning, and we saw this amazing signal in the data that seemed it was a really strong signal – not what anyone was expecting at all. I was expecting, if we did detect a gravitational wave, it would be some tiny signal lost in the noise.

“I was like, ‘Yeah, pull the other one’, you know. It’s too perfect a timing to get this signal just after everything was ready to detect a signal.

“It was actually in the engineering run, so we weren’t actually officially in the beginning of the observing run.”

The discovery wasn’t made public until February the next year, when the LIGO team published their findings, identifying the source of the signal as a collision of two black holes, each with a mass about 30 times that of our Sun.

In the aftermath of the collision, just one black hole remained, and it was “ringing like a bell”, Blair said.

“Imagine if you had a droplet of water in the air, and you gave it a flick, that droplet of water would jiggle around,” he said.

“The black hole does the same thing. After two black holes collide, the thing jiggles around for a bit, and from that signal, you can tell how big the final black hole is.”

Theoretical physicist Albert Einstein had predicted gravitational waves a century earlier, with his theory of general relativity painting a picture of a universe where space and time were intrinsically connected and warped by massive objects, which gave rise to gravity.

The detection at LIGO yet again proved his theory accurate, and has since opened a new window through which to view the universe, with hundreds more “coalescence events” detected in the years after.

“LIGO is now detecting about three black hole collisions every three days,” Blair said.

“And that’s not all of them. In the future – like in the next 10 or 20 years – we want to build more-sensitive detectors, where we’ll be detecting all the black holes in the visible universe, there’s also going to be a detector – LISA – put up in space, and we’re expecting to be detecting signals every minute, that kind of thing.

“What was surprising is, before the first observation of gravitational waves, we didn’t know that such heavy black holes existed.

“Most people had predicted that we’d first detect neutron stars colliding, because we had an idea how many neutron stars there are in our galaxy.

“We didn’t know these 30-solar-mass black holes existed. Nobody had observed a 30-solar mass-black hole before gravitational waves.

“And now, after a decade of observing, we’ve detected over 300 of these signals, and the vast majority of them are black holes, and most of them are heavy black holes.”

UWA will host a panel commemorating a decade since the discovery on Thursday, with Blair chairing it, with astronomers and researchers discussing the discovery and what lies ahead in the field, including a potential gravitational wave observatory in Australia.

Blair said plans had been afoot for an Australian observatory for many years, and with the establishment of the ARC Centre of Excellence for Gravitational Wave Discovery – or, OzGrav – he hoped those plans would come to fruition in the coming decade.