A second gravitational wave has been detected by LIGO

The LIGO team reported on June 15, 2016, their second confirmed detection of coalescing binary black hole pair generating a gravitational wave. This was published in Physical Review Letters,1 with an abstract that reads (with some editing in […]’s and emphases added):

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 5σ. 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 [about] 3.4 × 10-22. The inferred source-frame initial black hole masses are 14.2  and 7.5 [solar masses, i.e. mass of the sun], and the final black hole mass is 20.8 [solar masses]. 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  Mpc [about 1.4 billion light-years] corresponding to a redshift of 0.09±0.03. All uncertainties define a 90% credible interval.

second g wave

Estimated gravitational-wave strain from GW151226 projected onto the LIGO Livingston detector with times relative to December 26, 2015 at 03:38:53.648 UTC. This shows the full bandwidth, without the filtering used for Fig. 1. Top: The 90% credible region for a nonprecessing spin waveform-model reconstruction (gray) and a direct, nonprecessing numerical solution of Einstein’s equations (red) with parameters consistent with the 90% credible region. Bottom: The gravitational-wave frequency f (left axis) computed from the numerical-relativity waveform. The cross denotes the location of the maximum of the waveform amplitude, approximately coincident with the merger of the two black holes. During the inspiral, f can be related to an effective relative velocity (right axis) given by the post-Newtonian parameter v/c=(GMπf/c^3)^1/3 , where M is the total mass. (Click on image for larger version.)

This result further strengthens the argument for stellar mass size black holes and for their correct prediction by Einstein’s general relativity. As I have written before this largely falls into the category of operational science. Some assumptions are necessarily required, but the waveform (see right) extracted from the received signal very precisely matches the expected waveform. Read What impact does the detection of gravitational waves have on biblical creation?2 Continue reading