First detection of gravitational waves

On 11 February 2016, an international team of scientists from the LIGO Scientific Collaboration and the Virgo Collaboration announced that they had discovered gravitational waves using the Advanced Laser Interferometer Gravitational-Wave Observatory, at two sites in the USA.

LIGO consists of two sites, Hanford, Washington, USA, and Livingston, Louisiana, USA. Each site is home to two perfectly straight and level 4-km steel vacuum tubes at right angles to each other. Using a technique known as interferometry, lasers are fired down the tubes and interfere with each other in detectors, allowing tiny fluctuations in space time to be observed. From 2002 to 2010, LIGO failed to detect any gravitational waves. A major upgrade over several years was completed in 2015, and LIGO detected its first gravitational waves on 14 September 2015, before the upgraded facility had officially begun science operations.

The gravitational waves detected are believed to be the result of two black holes, around 36 and 29 solar masses, merging in a galaxy around 1.3 billion light years away.

Gravitational waves were predicted by Albert Einstein’s general theory of relativity in 1916.