Tests of General Relativity with GW150914

TLDR

The LIGO detection of GW150914 offers a unique chance to study the dynamics of a compact‑object binary in the highly relativistic, nonlinear regime and to observe the final merger and associated relativistic gravitational‑wave modes. The authors aim to test whether GW150914 is consistent with a binary black‑hole merger described by general relativity. They employ parametrized waveform models that allow for general‑relativity violations during inspiral and merger to perform quantitative phase tests and to set the first empirical bounds on several high‑order post‑Newtonian coefficients. The remnant’s mass and spin agree with GR predictions, the post‑peak signal matches the expected quasinormal mode, the graviton Compton wavelength is bounded below by 10^13 km, and no evidence for GR violations was found.

Abstract

The LIGO detection of GW150914 provides an unprecedented opportunity to study the two-body motion of a compact-object binary in the large-velocity, highly nonlinear regime, and to witness the final merger of the binary and the excitation of uniquely relativistic modes of the gravitational field. We carry out several investigations to determine whether GW150914 is consistent with a binary black-hole merger in general relativity. We find that the final remnant's mass and spin, as determined from the low-frequency (inspiral) and high-frequency (postinspiral) phases of the signal, are mutually consistent with the binary black-hole solution in general relativity. Furthermore, the data following the peak of GW150914 are consistent with the least-damped quasinormal mode inferred from the mass and spin of the remnant black hole. By using waveform models that allow for parametrized general-relativity violations during the inspiral and merger phases, we perform quantitative tests on the gravitational-wave phase in the dynamical regime and we determine the first empirical bounds on several high-order post-Newtonian coefficients. We constrain the graviton Compton wavelength, assuming that gravitons are dispersed in vacuum in the same way as particles with mass, obtaining a 90%-confidence lower bound of 10^{13} km. In conclusion, within our statistical uncertainties, we find no evidence for violations of general relativity in the genuinely strong-field regime of gravity.