Abstract
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−γ)σ
divides the whole spacetime into two regions, where the internal
region is de Sitter, and the external one is Schwarzschild. When
γ<1
and 
, it is found that in some cases the models represent stable gravastars, and
in some cases they represent 'bounded excursion' 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 occurs. However, when
γ≥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, although
it is not completely empty.