black holes

On 26 December 2015, LIGO detected gravitational waves from two black holes spiraling together.

LIGO/T. Pyle

The search for gravitational waves

Physicists have sought to detect ripples in spacetime called gravitational waves ever since they realized Albert Einstein’s general theory of relativity predicted their existence. But only some of the most massive astrophysical events, such mergers of black holes and neutron stars, can produce gravitational waves strong enough to be detected on earth. Since the 1990s, two laser-based facilities in Washington and Louisiana, collectively known as LIGO, have tried to observe waves from such events. They finally detected the first gravitational wave last September, as announced on 11 February.  Recent LIGO upgrades, including more sensitive instruments and incorporation of detectors around the world, should bring the detection of many more waves and open up a whole new way of viewing cataclysmic events in the universe.