Since its prediction by Einstein a century ago as a consequence of the general theory of relativity, gravitational radiation has posed a daunting technical challenge, requiring enormously accurate differential length measurements for detection.
The first observation of gravitational waves of astrophysical origin was made by the recently upgraded Advanced LIGO
detectors in September 2015, the source being the merger of two black holes, each more massive than any previously observed in a stellar system.
From data gathered up to January 2016, a second detection and a likely third candidate signal began to reveal a population of binary black hole mergers occurring at a rate close to plausible maximum estimates for standard formation channels. Tests of the strong-field behaviour of gravity using these events showed no deviations from the predictions of general relativity.
After this spectacular beginning, the next few years will bring the operation of a global network with the Virgo and KAGRA detectors and the possible detection of merging binary systems containing neutron stars which may yield electromagnetic and neutrino signatures.