Where are all the gravastars? Limits upon the gravastar model from accreting black holes

TL;DR

This paper examines observational constraints on the gravastar model as an alternative to black holes, focusing on low-luminosity black hole candidates and finding that modifications must occur at sub-Planckian scales.

Contribution

It provides the first observational limits on gravastar models using data from well-known black hole candidates.

Findings

Constraints imply modifications occur at sub-Planckian scales.

Low-luminosity black holes strongly restrict gravastar parameters.

The gravastar model faces significant observational challenges.

Abstract

The gravastar model, which postulates a strongly correlated thin shell of anisotropic matter surrounding a region of anti-de Sitter space, has been proposed as an alternative to black holes. We discuss constraints that present-day observations of well-known black hole candidates place on this model. We focus upon two black hole candidates known to have extraordinarily low luminosities: the supermassive black hole in the Galactic Center, Sagittarius A*, and the stellar-mass black hole, XTE J1118+480. We find that the length scale for modifications of the type discussed in Chapline et al. (2003) must be sub-Planckian.