Sub-atomic constraints on the Kerr geometry of GW150914

TL;DR

This paper uses gravitational wave data from GW150914 to place tight constraints on deviations from the Kerr black hole geometry, supporting the black hole nature of the final object.

Contribution

It introduces a novel Bayesian analysis method to test for horizonless ultracompact objects by searching for long-lived quasinormal modes in gravitational wave data.

Findings

No evidence of horizonless ultracompact objects was found.

Constraints on deviations from Kerr geometry are as small as 5.8 x 10^{-19} meters from the horizon.

Results support the Kerr black hole model for GW150914's final object.

Abstract

We obtain stringent constraints on near-horizon deviations of a black hole from the Kerr geometry by performing a long-duration Bayesian analysis of the gravitational-wave data immediately following GW150914. GW150914 was caused by a binary system that merged to form a final compact object. We parameterize deviations of this object from a Kerr black hole by modifying its boundary conditions from full absorption to full reflection, thereby modeling it as a horizonless ultracompact object. Such modifications result in the emission of long-lived monochromatic quasinormal modes after the merger. These modes would extract energy on the order of a few solar masses from the final object, making them observable by LIGO. By putting bounds on the existence of these modes, we show that the Kerr geometry is not modified down to distances as small as $5.8 \times 10^{-19}$ meters away from the horizon. Our results indicate that the post-merger object formed by GW150914 is a black hole that is well described by the Kerr geometry.