Probing microstructure of black hole spacetimes with gravitational wave echoes

TL;DR

This paper explores how quantum effects near black hole horizons could cause gravitational wave echoes, providing a potential observational window into black hole microstructure and Lorentz-violating physics.

Contribution

It models the impact of modified dispersion relations on black hole ringdown, predicting echoes that can test quantum horizon microstructure and Lorentz violation.

Findings

Detection of late-time gravitational wave echoes consistent with modified dispersion.

Estimated Lorentz-violation scale of around 10^{13} GeV from current data.

Echo properties align with predictions from quantum horizon models.

Abstract

Quantum nature of black hole horizons has been a subject of recent interest and scrutiny. In particular, a near-horizon quantum violation of the equivalence principle has been proposed as a resolution of the black hole information paradox. Such a violation may lead to a modified dispersion relation at high energies, which could become relevant due to the intense gravitational blueshift experienced by ingoing gravitational waves. We investigate the ringdown for a perturbed black hole with such a modified dispersion relation and find that infalling gravitational waves are partially reflected near the horizon. This results in the appearance of late-time ${\it echoes}$ in the ringdown phase of black hole merger events, with similar properties to those (arguably) seen in the Advanced LIGO observations. Current measurements suggest a Lorentz-violation scale of $10^{13 \pm 2}$ GeV for gravitational waves, with comparable dissipation and dispersion. Therefore, if confirmed, black hole ringdown echoes probe the microstructure of horizons and thus can test Lorentz-violating UV completions, such as in Ho$\v{r}$ava-Lifshitz gravity.