Stable and ‘bounded excursion’ gravastars, and black holes in Einstein’s theory ofgravity

Abstract

Dynamical models of prototype gravastars are constructed and studied.The models are the Visser–Wiltshire three-layer gravastars, in which aninfinitely thin spherical shell of a perfect fluid with the equation of statep = (1−γ)σ divides the whole spacetime into two regions, where the internalregion is de Sitter, and the external one is Schwarzschild. Whenγ<1 and , it is found that in some cases the models represent stable gravastars, andin some cases they represent ‘bounded excursion’ stable gravastars, wherethe thin shell is oscillating between two finite radii, while in some othercases they collapse until the formation of black holes occurs. However, whenγ≥1, even with , only black holes are found. In the phase space, the region for both stable gravastars and‘bounded excursion’ gravastars is very small in comparison to that for black holes, althoughit is not completely empty.