Testing the"no-hair" nature of binary black holes using the consistency of multipolar gravitational radiation

TL;DR

This paper develops methods to test the consistency of gravitational-wave signals with the multipolar structure predicted by general relativity for binary black holes, aiming to verify the 'no-hair' nature of these objects.

Contribution

The paper introduces multiple new tests for the multipolar structure of gravitational waves, extending previous work to better verify the 'no-hair' theorem in binary black hole systems.

Findings

Bayesian inference demonstrates the effectiveness of the tests on simulated signals.

The tests can distinguish between GR-consistent and inconsistent signals.

Systematic errors from neglecting spins are quantitatively estimated.

Abstract

Gravitational-wave (GW) observations of binary black holes offer the best probes of the relativistic, strong-field regime of gravity. Gravitational radiation, in the leading order is quadrupolar. However, non-quadrupole (higher-order) modes make appreciable contribution to the radiation from binary black holes with large mass ratios and misaligned spins. The multipolar structure of the radiation is fully determined by the intrinsic parameters (masses and spin angular momenta of the companion black holes) of a binary in quasi-circular orbit. Following our previous work \cite{Dhanpal:2018ufk}, we develop multiple ways of testing the consistency of the observed GW signal with the expected multipolar structure of radiation from binary black holes in general relativity. We call this a "no-hair" test of binary black holes as this is similar to testing the "no-hair" theorem for isolated black holes through mutual consistency of the quasi-normal mode spectrum. We use Bayesian inference on simulated GW signals that are consistent/inconsistent with binary black holes in GR to demonstrate the power of the proposed tests. We also make estimate systematic errors arising as a result of neglecting companion spins.