Stable and "bounded excursion" gravastars, and black holes in Einstein's theory of gravity

Understand

Dynamical models of prototype gravastars are constructed and studied.

• The models are the Visser-Wiltshire three-layer gravastars, 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, where the internal region is de Sitter, and the external is Schwarzschild.
• When $\gamma < 1$ and $\Lambda \not= 0$, it is found that in some cases the models represent stable gravastars, and in some cases they represent &#34;bounded excursion&#34; stable gravastars, where the thin shell is oscillating between two finite radii, while in some other cases they collapse until the formation of black holes.
• However, when $\gamma \ge 1$, even with $\Lambda \not= 0$, only black holes are found.