How to tell a gravastar from a black hole

TL;DR

This paper investigates whether gravastars can be distinguished from black holes by analyzing their stability and quasi-normal modes, finding that gravastars are stable and have unique signatures that can be observationally identified.

Contribution

The study constructs a general class of gravastar models, analyzes their stability against axial perturbations, and demonstrates their quasi-normal modes differ from black holes, enabling observational distinction.

Findings

Gravastars are stable against axial perturbations.

Quasi-normal modes of gravastars differ from black holes.

Distinct signatures allow observational differentiation.

Abstract

Gravastars have been recently proposed as potential alternatives to explain the astrophysical phenomenology traditionally associated to black holes, raising the question of whether the two objects can be distinguished at all. Leaving aside the debate about the processes that would lead to the formation of a gravastar and the astronomical evidence in their support, we here address two basic questions: Is a gravastar stable against generic perturbations? If stable, can an observer distinguish it from a black hole of the same mass? To answer these questions we construct a general class of gravastars and determine the conditions they must satisfy in order to exist as equilibrium solutions of the Einstein equations. For such models we perform a systematic stability analysis against axial-perturbations, computing the real and imaginary parts of the eigenfrequencies. Overall, we find that gravastars are stable to axial perturbations, but also that their quasi-normal modes differ from those of a black hole of the same mass and thus can be used to discern, beyond dispute, a gravastar from a black hole.