The first detected gravitational waves were generated by the merger of two black holes, a cataclysmic event known as a binary black hole merger. These gravitational waves were detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) on September 14, 2015.
The binary black hole system that produced the gravitational waves was located approximately 1.3 billion light-years away from Earth. Light-years are a unit of distance, measuring the distance that light travels in one year. Since gravitational waves travel at the speed of light, it took approximately 1.3 billion years for the waves to reach Earth after they were emitted in space.
The detection of gravitational waves by LIGO confirmed a major prediction of Albert Einstein's theory of general relativity and opened up a new window of observation for studying the universe. It marked the beginning of a new field of astrophysics called gravitational wave astronomy.