A GW detection (gravitational wave detection) is the reception of a gravitational wave (GW) pattern that is recognized as the signal of an astronomical event (a gravitational wave event or GW event) by a gravitational-wave detector such as LIGO. Detections so far have mostly been GWs from black hole mergers, but a few from mergers including neutron stars. Detecting these merger signals has been the aim of these first ground-based GW detectors: the merger process had been analyzed regarding the signal they would produce and the successful detections confirm current science of black holes and neutron stars as well as the general relativity model of gravity.
The merger signal is a chirp (waves rising in frequency, from quicker and quicker orbits preceding the impact), followed by a short period of lesser waves, the ringdown (waves from some further repositioning of mass just after the impact, i.e., the recoil). To be recognized, the signal must show a pattern distinct from the gravitational wave background. The signal reveals information analytically (e.g., the chirp mass), and more through numerical simulation of objects of various sizes and rotations. There is an inclination-distance degeneracy because the signal is to some degree directional: if viewed from edge-on to the orbit, the signal is twice as strong as if viewed from perpendicular to the orbit. The ringdown signal helps reduce this ambiguity. If information regarding the alignment of the merging objects' rotations can be deduced, that would provide evidence whether the two objects were born as a binary star versus some sort of capture.
The first six detections accepted:
|GW150914||black holes||LIGO||first detection|
|GW170817||neutron stars||LIGO/Virgo||location and source spotted|
Subsequently, some additional candidate detections within the above time period have been accepted as real. As of 2/2020 there have been over 60 detections and candidate events, including additional neutron star mergers and some black hole/neutron star mergers.