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

TLDR

The GW151226 signal was detected by LIGO’s twin detectors on 26 Dec 2015 and identified within 70 s by an online matched‑filter search for binary coalescences. GW151226, a 1‑s gravitational‑wave burst from a 22‑solar‑mass binary black‑hole merger at ~440 Mpc, achieved a network SNR of 13, a >5σ significance, component masses 14.2 M⊙ and 7.5 M⊙, a final mass of 20.8 M⊙, at least one spin >0.2, and provides tighter constraints on stellar populations and deviations from general relativity.

Abstract

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 $\sigma$. 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 $3.4_{-0.9}^{+0.7} \times 10^{-22}$. The inferred source-frame initial black hole masses are $14.2_{-3.7}^{+8.3} M_{\odot}$ and $7.5_{-2.3}^{+2.3} M_{\odot}$ and the final black hole mass is $20.8_{-1.7}^{+6.1} M_{\odot}$. 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 $440_{-190}^{+180}$ Mpc corresponding to a redshift $0.09_{-0.04}^{+0.03}$. All uncertainties define a 90 % credible interval. This second gravitational-wave observation provides improved constraints on stellar populations and on deviations from general relativity.