First observation of gravitational waves

The first direct detection of gravitational waves, made by LIGO in 2015 from two merging black holes and announced in 2016 as GW150914.

GW150914: The gravitational-wave signal detected by LIGO on September 14, 2015, from the merger of two black holes. This is the specific event that constituted the first observation.
Gravitational wave: A propagating disturbance in spacetime produced by accelerating masses and traveling at the speed of light. The observed signal was the first direct detection of this predicted phenomenon.
Gravitational-wave astronomy: The study of cosmic objects and events through gravitational waves detected on Earth or in space. GW150914 began direct observational astronomy using gravitational waves.
GW150914 signal: The measured strain pattern associated with the gravitational-wave event GW150914. Its characteristic rising frequency and amplitude identified the final inspiral and merger.
Laser Interferometer Gravitational-Wave Observatory: A pair of large laser interferometers in the United States designed to detect gravitational waves. Its two detectors recorded the signal that established the observation.
General relativity: Albert Einstein’s theory of gravity, in which matter and energy shape spacetime and its curvature governs motion. Einstein’s theory predicted gravitational waves and supplied the framework for interpreting the event.
Multi-messenger astronomy: The study of astronomical events using multiple kinds of signals, such as light, neutrinos, and gravitational waves. The first detection established gravitational waves as a new astronomical messenger, even without a known light counterpart.
Gravitational-wave strain: The fractional change in distance between freely falling points caused by a gravitational wave. LIGO’s recorded strain captured the extremely small effect of the event on its interferometers.
Michelson interferometer: An optical instrument that measures differences in the distances traveled by light along two perpendicular arms. LIGO uses this design to measure tiny changes in arm length caused by passing waves.
Joseph Weber: An American physicist who pioneered experiments to detect gravitational waves with resonant aluminum bars. His early detector efforts helped establish gravitational-wave detection as an experimental goal.

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