GW151226: Observation of Gravitational Waves from a 22-Solar-Mass Binary Black Hole Coalescence

We report the observation of a gravitational-wave signal produced by the coalescence of two stellar-mass black holes. The signal, GW151226, was observed by the twin detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) on December 26, 2015 at 03:38:53 UTC. The signal was initially identified within 70 s by an online matched-filter search targeting binary coalescences. Subsequent off-line analyses recovered GW151226 with a network signal-to-noise ratio of 13 and a significance greater than 5 σ . The signal persisted in the LIGO frequency band for approximately 1 s, increasing in frequency and amplitude over about 55 cycles from 35 to 450 Hz, and reached a peak gravitational strain of 3. 4_-0.9^+0.7×10^-22 . The inferred source-frame initial black hole masses are 14.2_-3.7^+8.3 M_⊙ and 7. 5_-2.3^+2.3 M_⊙, and the final black hole mass is 20.8_-1.7^+6.1 M_⊙. We find that at least one of the component black holes has spin greater than 0.2. This source is located at a luminosity distance of 44 0_-190⁺¹⁸⁰ Mpc corresponding to a redshift of 0.0 9_-0.04^+0.03. All uncertainties define a 90% credible interval. This second gravitational-wave observation provides improved constraints on stellar populations and on deviations from general relativity.