Gravitational wave echoes through new windows

TL;DR

This paper presents evidence for gravitational wave echoes from multiple LIGO events, suggesting possible new physics related to black hole horizons, and develops methods to detect and analyze these echoes.

Contribution

It provides the first evidence of gravitational wave echoes across several events and introduces new windowing techniques to extract these signals from noisy data.

Findings

Evidence for echoes with p-value around 1% in multiple events

Time delays consistent with models based on mass and spin

Constraints on final mass and spin for neutron star merger

Abstract

There has been a striking realization that physics resolving the black hole information paradox could imply postmerger gravitational wave echoes. We here report on evidence for echoes from the LIGO compact binary merger events, GW151226, GW170104, GW170608, GW170814, as well as the neutron star merger GW170817. There is a signal for each event with a $p$-value of order 1% or sometimes significantly less. Our study begins with the comparison of echoes from a variety of horizonless exotic compact objects. Next we investigate the effects of spin. The identification of the more generic features of echoes then leads to the development of relatively simple windowing methods, in both time and frequency space, to extract a signal from noise. The time delay between echoes is inversely related to the spacing between the spectral resonances, and it is advantageous to look directly for this resonance structure. We find time delays for the first four events that are consistent with a simple model that accounts for mass and spin of the final object, while for the neutron star merger the final mass and spin are constrained.