Hierarchical constraints on gravitational waves from horizonless compact objects

TL;DR

This paper uses gravitational wave data to set stringent bounds on horizonless compact objects' deviations from Kerr black holes, improving previous limits by combining multiple events and modeling gravitational wave reflections.

Contribution

It introduces a hierarchical method to combine gravitational wave data, providing the tightest bounds on near-horizon deviations for horizonless objects.

Findings

Bound on deviations less than 2.5 x 10^{-26} meters.

Extended analysis to 5 additional gravitational wave events.

Improved constraints compared to previous individual event analyses.

Abstract

We use the data of several promising gravitational wave observations to obtain increasingly stringent bounds on near-horizon deviations of their sources from the Kerr geometry. A range of horizonless compact objects proposed as alternatives to black holes of general relativity would possess a modified gravitational wave emission after the merger. Modelling these objects by introducing reflection of gravitational waves near the horizon, we can measure deviations from Kerr in terms of a single additional parameter, the location of the reflection. We quote bounds on deviations for 5 events in addition to previous results obtained for GW150914. Additionally, we improve upon previous results by hierarchically combining information from all analysed events, yielding a bound on deviations of less than $2.5 \times 10^{-26}$ meters above the horizon.