Stable Gravastars of Anisotropic Dark Energy

TL;DR

This paper models gravastars composed of anisotropic dark energy, showing they can be stable or collapse into black holes, and discusses their potential coexistence with black holes.

Contribution

It introduces a new dynamical model of gravastars with anisotropic dark energy and analyzes their stability and phase space characteristics.

Findings

Stable 'bounded excursion' gravastars exist in limited phase space.

Collapse to black holes or stars is possible in other cases.

Gravastars' phase space is small but non-empty, not excluding their existence.

Abstract

Dynamical models of prototype gravastars made of phantom energy are constructed, in which an infinitely thin spherical shell of a perfect fluid with the equation of state $p = (1-\gamma)\sigma$ divides the whole spacetime into two regions, the internal region filled with a dark energy (or phantom) fluid, and the external Schwarzschild region. It is found that in some cases the models represent the "bounded excursion" stable gravastars, where the thin shell is oscillating between two finite radii, while in other cases they collapse until the formation of black holes or normal stars. In the phase space, the region for the "bounded excursion" gravastars is very small in comparison to that of black holes, but not empty, as found in our previous papers. Therefore, although the existence of gravastars can not be completely excluded from current analysis, the opposite is not possible either, that is, even if gravastars exist, they do not exclude the existence of black holes.