First observation of gravitational waves

The first observation of gravitational waves on 14 September 2015 was announced by the LIGO and Virgo interferometer collaborations on 11 February 2016. Gravitational waves had previously been observed only indirectly, through their effect on the timing of pulsars in binary systems. The waveform, detected by both LIGO observatories, matched the predictions of general relativity for a gravitational wave emanating from the inward spiral and merger of a pair of black holes and subsequent "ringdown" of the single resulting black hole. The signal was named GW150914 (i.e., "Gravitational Wave 2015-09-14"). It was also the first observation of a binary black hole merger, demonstrating the existence of binary stellar-mass black hole systems, and that such mergers could occur within the current age of the universe.

This first observation was reported around the world as a remarkable accomplishment for many reasons. Efforts to directly prove the existence of such waves had been ongoing for over fifty years, and the waves are so minuscule that Albert Einstein doubted they could ever be detected. The waves given off by the cataclysmic merger of GW150914 reached Earth as a ripple in spacetime that changed the length of a 4-km LIGO arm by a ten thousandth of the width of a proton, proportionally equivalent to changing the distance to the nearest star by one hair's width. The energy released during the brief climax of the event was immense, with about three solar masses converted to gravitational waves and radiated away at a peak rate of about 3.6×10⁴⁹ watts – more than the combined power of all light radiated by all the stars in the observable universe.