# Distinguishing black holes from horizonless objects through the excitation of resonances during inspiral

## TL;DR

This paper investigates whether resonant excitation of modes in horizonless, ultra-compact objects during inspiral can distinguish them from black holes, finding that resonances occur but have negligible impact on gravitational-wave signals.

## Contribution

It demonstrates that resonances are excited in horizonless objects during inspiral, but their effect on gravitational waves is minimal, aiding in distinguishing black holes from other compact objects.

## Key findings

- Resonances are excited in horizonless, ultra-compact objects during inspiral.
- The impact of resonances on gravitational-wave phase is negligible.
- Resonance crossing occurs very quickly during inspiral.

## Abstract

How well is the vacuum Kerr geometry a good description of the dark, compact objects in our universe? Precision measurements of accreting matter in the deep infrared and gravitational-wave measurements of coalescing objects are finally providing answers to this question. Here, we study the possibility of resonant excitation of the modes of the central object -- taken to be very compact but horizonless -- during an extreme-mass-ratio inspiral. We show that for very compact objects resonances are indeed excited. However, the impact of such excitation on the phase of the gravitational-wave signal is negligible, since resonances are crossed very quickly during inspiral.