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 70s 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 5σ. The signal persisted in the LIGO frequency band for approximately 1s, increasing in frequency and amplitude over about 55 cycles from 35 to 450Hz, 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 440_{-190}^{+180} Mpc corresponding to a redshift of 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.
Highlights
A century after Einstein predicted the existence of gravitational waves [1], the Laser Interferometer Gravitational-Wave Observatory (LIGO) [2,3] observed the first gravitational-wave signal GW150914 from a binary black hole merger [4]
Based on current waveform modeling, we find that GW151226 passed through LIGO’s sensitive band in 1 s, increasing in frequency over approximately 55 cycles
LIGO has detected a second gravitational-wave signal from the coalescence of two stellar-mass black holes with lower masses than those measured for GW150914
Summary
A century after Einstein predicted the existence of gravitational waves [1], the Laser Interferometer Gravitational-Wave Observatory (LIGO) [2,3] observed the first gravitational-wave signal GW150914 from a binary black hole merger [4]. LVT151012, the third most significant binary black hole candidate, is included in this analysis (see Fig. 2 below). No other significant binary black hole candidates in the total mass range 4–100M⊙ were found during Advanced LIGO’s first observing period, September 12, 2015 to January 19, 2016. Detection [13,14,15,16,17,18] and parameter estimation [19,20,21] rely on understanding the sources of detector noise [22,23] and on precise waveform models of compact binary coalescence. Matched filtering correlates a waveform model with the data over the detectors’ sensitive band, which enabled GW151226 to be extracted from the detector noise
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