Gravitational waves are oscillations in spacetime curvature that originate from binary systems of extremely dense objects like black holes or neutron stars.
In this case, two black holes with masses of 29 and 36 M☉ gradually lost gravitational energy and began to inspiral. Their mutual orbital diameter decreased and they coalesced into a single black hole with a mass of 62 M☉. The lost gravitational energy and remaining 3 solar masses were radiated in these gravitational waves.
The resulting ripples propagated through spacetime to Earth, where they expanded and contracted LIGO's detectors by a factor of 10
-21, or about 10 times the size of an atomic nucleus. The closer an object is to the wave source, the greater the amplitude of the wave and the more objects are distorted.
The gravitational wave data was made public by the LIGO Scientific Collaboration (LSC) and the Virgo Collaboration. It signals the beginning of a new era of gravitational wave physics and reveals previously undetectable information about the origins of the universe.