The existence of gravitational waves has been confirmed for the first time, after scientists from the Laser Interferometer Gravitational-Wave Observatory (LIGO) detected direct evidence of the phenomenon.
“We have detected gravitational waves. We did it!” said David Reitze, laboratory executive director at LIGO, in a press conference watched by tens of thousands from around the world. “I am so pleased to be able to tell you that.”
The cause of these particular gravitational waves was the colliding of two black holes, an incredible occurrence that has also never before been documented.
“These gravitational waves were produced by two colliding black holes that came together and merged to form a single black hole about 1.3 billion years ago,” said Reitze.
“On September 14th 2015, the two LIGO observatories in Hanford, Washington and Livingston, Louisiana, recorded a signal at nearly the same time, and the signal had a very specific characteristic – as time went forward, the frequency went up,” he added.
“What was amazing about this signal is that it’s exactly what you would expect – what Einstein’s theory of General Relativity would predict – for two massive objects like black holes merging together.”
The scientists were able to accurately model the behaviour of the black holes, producing a visualisation that Reitze narrated.
“As they orbit the black holes are getting closer and closer to one another, the orbit is speeding up, and eventually they’re going to merge – the event horizons are going to join: boom, they produce one big black hole,” he said.
“What’s really amazing about this is this is the first time that this kind of a system has ever been seen – a binary black hole merger – and its proof that binary black holes exist in the universe.”
The merging action of these black holes resulted in gravitational waves being ejected outwards, like a ripple when a stone hits water. As the waves can pass through matter, they have continues to travel outwards for 1.3 billion years, until they passed Earth last September, and were detected by LIGO.
“There’s this burst of gravitational waves that travels for 1.3 billion years, it passes through everything, it goes right through matter, right through stars, and it eventually gets to the Earth,” said Reitze.
When the gravitational waves passed through Earth, they stretched and compressed space, which is what LIGO was able to detect. However, this effect is so small that is required exceptionally sensitive detection, which may explain why LIGO is, as Reitze puts it, “the most precise measuring device ever built“.
“The effect we’re trying to measure from these big black holes colliding at half the speed of light is so tiny that it takes something like LIGO to measure it,” he said. “We are trying to measure things basically at 1/1000 the diameter of a proton. That’s the size of the signal that you see on Earth from those events that take place 1.3 billion years away. “
He added that if LIGO were to measure the distance between our sun and the next nearest star, it would be “capable of measuring that to the width of a human hair”. Incredibly, it also allows scientists to listen to the phenomenon.
“What LIGO does is it takes these ripples in spacetime and it records them on a photodetector, and you can actually hear them,” he said. “It’s the first time the universe has spoken to us in gravitational waves; up until now we’ve been deaf to gravitational waves, but today we are able to hear them.”