LIGO first detected gravitational waves from merging black holes in 2015.
The Laser Interferometer Gravitational-Wave Observatory, or LIGO, made the first direct detection on September 14, 2015. The signal, called GW150914, came from the merger of two black holes about 1.3 billion light-years away. Scientists announced the discovery in February 2016, confirming a major prediction of Einstein’s general theory of relativity.
LIGO is not a single conventional telescope. It is a pair of enormous laser interferometers, one in Livingston, Louisiana, and the other in Hanford, Washington. Each facility has perpendicular arms four kilometers long. A passing gravitational wave changes the arm lengths by an extraordinarily tiny amount, allowing the instruments to detect ripples in spacetime rather than visible light.
The wording can cause a small conceptual mix-up: both LIGO observatories detected the event, so “LIGO” is the canonical answer rather than either site alone. Keck, ALMA, and the VLA are important astronomical facilities, but they observe electromagnetic signals and were not the instruments that made this first direct gravitational-wave detection.