Ergoregion instability of ultra-compact astrophysical objects

TL;DR

This paper demonstrates that rapidly spinning ultra-compact horizonless objects are unstable due to ergoregion effects, strongly suggesting such objects are actually black holes, with potential gravitational-wave signatures detectable by future observatories.

Contribution

It shows that ergoregion instability occurs in ultra-compact objects with high spin, providing a new criterion to distinguish black holes from horizonless objects.

Findings

Ultra-compact objects with high spin develop ergoregion instability.

Instability timescales range from 0.1 seconds to 1 week for certain masses.

Potential gravitational-wave signatures could be detected by future detectors.

Abstract

Most of the properties of black holes can be mimicked by horizonless compact objects such as gravastars and boson stars. We show that these ultra-compact objects develop a strong ergoregion instability when rapidly spinning. Instability timescales can be of the order of 0.1 seconds to 1 week for objects with mass M=1-10^6 solar masses and angular momentum J> 0.4 M^2. This provides a strong indication that ultra-compact objects with large rotation are black holes. Explosive events due to ergoregion instability have a well-defined gravitational-wave signature. These events could be detected by next-generation gravitational-wave detectors such as Advanced LIGO or LISA.