Gravitational waves caused by colliding black holes In February 2016, a team of US scientists announced that they had detected gravitational waves. These are the ripples in “space-time” that were predicted a century ago by the great German scientist Albert Einstein (1879–1955) in his General Theory of Relativity. Clear signals from the waves had been picked up by LIGO, or the Advanced Laser Interferometer Gravitational-Wave Observatory. The team used detectors in Washington and Louisiana to spot passing gravitational waves produced, they believe, by the collision of two black holes.
Ripples in space
Gravitational waves are like the ripples on a pond created when a pebble is thrown into it. The pond is made not of water, but space (or, strictly speaking, what Einstein called space-time). If, instead of a pebble, something really massive is thrown into that “pond”—such as two black holes colliding—the resulting ripples would spread out across the Universe. These ripples—gravitational waves—would stretch and squeeze space, and everything within it, as they went.
The LIGO apparatus is the most sensitive measuring device on Earth. It can detect vibrations from passing trucks hundreds of kilometres away.
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