GW170608: Observation of a 19-solar-mass binary Black Hole coalescence

On June 8, 2017 at 02:01:16.49 UTC, a gravitational-wave signal from the merger of two stellar-mass black holes was observed by the two Advanced LIGO detectors with a network signal-to-noise ratio of 13. This system is the lightest black hole binary so far observed, with component masses 12+7?2M? and 7+2?2M? (90% credible intervals). These lie in the range of measured black hole masses in low-mass X-ray binaries, thus allowing us to compare black holes detected through gravitational waves with electromagnetic observations. The source's luminosity distance is 340+140?140 Mpc, corresponding to redshift 0.07+0.03?0.03. We verify that the signal waveform is consistent with the predictions of general relativity.