Resonances, black hole mimickers and the greenhouse effect: consequences for gravitational-wave physics

TL;DR

This paper challenges previous assumptions about black hole mimickers by showing that their internal structure effects are delayed, making them behave more like true black holes in gravitational-wave signals.

Contribution

It demonstrates that the stationary regime assumption is invalid initially, affecting the interpretation of resonances and tidal effects in gravitational-wave observations.

Findings

Black hole mimickers behave more like black holes than previously thought.

Delay in 'charging-up' affects the detection of resonances.

Implications for gravitational-wave tests of horizon physics.

Abstract

Ultracompact objects with photonspheres are known to mimic many observational features of black holes. It has been suggested that anomalous tidal heating or the presence of resonances in gravitational wave signals would be a clear imprint of a surface or absence of a horizon. Such claims and studies are all based on a frequency-domain analysis, assuming stationarity. Here we show that the object needs to first "fuel-up" until it reaches the stationary regime. The presence of a stable light ring and large light-travel times inside the object may in fact delay enormously the "charging-up" and effectively contribute to the effacement of structure. In other words, black hole mimickers behave as black holes more efficiently than previously thought. Our results have implications for other resonant systems with sharp resonances, including "floating orbits" around spinning black holes. A proper accounting of the self-force for such systems seems to be both mandatory, and would have important applications for tests of horizon physics.