Einstein’s Gravitational Waves

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  Last updated November 6, 2017 at 1:39 pm


A still image from the Hubble Space Telescope observes the source of gravitational waves for the first time. Image: Hubble ESA, flickr

Scientists made headlines around the world in 2016 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 100 years ago.

But what exactly are gravitational waves?

Gravitational waves are caused by objects of strong gravity accelerating at a rate that deforms the fabric of space itself.

This is because in Einstien’s Universe gravity isn’t a force like the way we usually think about forces. Gravity is just what happens when large objects bend the fabric of space-time creating curves for other objects to follow.

So when you have an event like two objects with very strong gravity accelerating, say like two black holes colliding, it causes ripples in space-time known as gravitational waves.

These waves are actual waves in space, stretching and contracting space, the Earth and us.

But while the events that create gravitational waves are huge, the actual waves are incredibly small and we cannot feel them.

Finding gravitational waves requires scientists to measure something that is 10,000 times shorter than the width of a proton.

To capture these signals, scientists measure the precise distance of lasers between a system mirrors located four kilometres apart. Any change in the distance would mean a gravitational wave passing through.

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 Australian National University, its runner-up status is what gives it 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 Australian National University. “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.

This article was written by Tabitha Carvan for the ScienceWise blog. ScienceWise is all about sharing the impact that STEM (science, technology, engineering and mathematics) has on our lives, and is proudly supported by the Australian National University.

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