On September 14th, 2015, both Advanced LIGO detectors in the USA, H1 in Hanford, Washington and L1 in Livingston, Louisiana, made the first direct measurement of a GW signal. The event, GW150914, was determined to be the merger of two black holes, with masses of 36 M⊙
and 29 M⊙
, into a black hole of approximately 62 M⊙
. 3.0 solar masses of energy (5.4 × 1047
J) were radiated in GWs. The gravitational waves from this event, which occurred at a distance of 410 Mpc (1.3 x 109
light years), changed the separation between the test masses by 4×10−18
m, about one 200th of a proton radius. Since this first detection of GWs, there were 11 confirmed detections during first and second observation runs (2015-2017) and 56 candidates detected during the third observing run (2019-2020). The first results of the latest run have already shown the huge potential of gravitational waves to reveal new astrophysical events : the number of interesting candidates, including the two neutron star systems, potentially the first black-hole--neutron-star merger and asymmetric collisions.
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