Gravitational waves detected. Again. Why should we care?


Written by Tabitha Carvan

Scientists made headlines around the world earlier this year when they confirmed the existence of gravitational waves. It was hailed as the scientific breakthrough of our lifetime, and earned blockbuster status in the world of science news thanks to a cameo role by Albert Einstein (who predicted the existence of gravitational waves exactly 100 years ago) and the repeated use of the phrase “a ripple in space-time”.

Now scientists have announced a second detection of gravitational waves at the same facility, the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the USA. The waves resulted from the same type of event as the first, the collision of two black holes.

Being pretty much a repeat of the first event, this news might seem like an anticlimactic sequel, but for scientists like Dr Robert Ward from the ANU Research School of Physics and Engineering, its runner-up status is what affords it such great importance.

“That’s actually what’s important about it, that it’s the second one,” he explains.

“We had been listening for gravitational waves for years using the first generation of detectors at LIGO and heard nothing. As soon as we switched on the upgraded second generation of detectors, we immediately heard the first signal, and it was a very big signal too.

“Because it happened straight away, we thought, wow, there must be gravitational waves from black holes merging all the time! But as we waited longer and longer, with no more black hole mergers, we started to wonder if it was a fluke, and maybe we just got really lucky.

“It was only when the second event showed up that we could know for sure that these events are happening regularly.”

If you consider this latest event as not merely the second one but the sign of many more to come, then you can understand Dr Ward’s excitement.

“We now know that if the detectors stayed at the same sensitivity, the rate of detection should be about one every month or two.

“Since we’re working to improve the sensitivity, in the future it should be even more.”

“This shows data is going to flow,” adds Professor Susan Scott, also from the ANU Research School of Physics and Engineering. “And that will enable us to map a lot more of the Universe than we’ve seen before.”

That mapping will continue in earnest as this second detection cements gravitational wave astronomy as the new primary tool for observing the Universe.

Eleven scientists from ANU made a critical contribution to getting LIGO ready for the detection of gravitational waves, and Dr Ward says that contribution will continue as they work to limit quantum noise on the LIGO interferometers.

Already thinking of the future, ANU will also contribute to the design and installation of hardware for the next generation of LIGO, which we now know is destined to make many more great big detections of very little waves.