STABLE DARK ENERGY STARS: AN ALTERNATIVE TO BLACK HOLES?

Abstract

In this work, a generalization of the Mazur-Mottola gravastar model is explored, by considering a matching of an interior solution governed by the energy equation of state, ! � p/� < 1/3, to an exterior Schwarzschild vacuum solution at a junction interface, situated near to where the event horizon is expected to form. The motivation for implementing this generalization arises from the fact that recent observations have confirmed an accelerated cosmic expansion, for which energy is a possible candidate. Although evidence for the existence of black holes is very convincing, a certain amount of scepticism regarding the physical reality of singularities and event hori- zons is still encountered. In part, due to this scepticism, an alternative picture for the final state of gravitational collapse has emerged, where an interior compact ob- ject is matched to an exterior Schwarzschild vacuum spacetime, at or near where the event horizon is expected to form. Therefore, these alternative models do not possess a singularity at the origin and have no event horizon, as its rigid surface is located at a radius slightly greater than the Schwarzschild radius. In particular, the gravastar (gravitational vacuum star) picture, proposed by Mazur and Mottola, 1 has an effective phase transition at/near where the event horizon is expected to form, and the interior is replaced by a de Sitter condensate. In this work, a generalization of the gravastar picture is explored, by considering a matching of an interior solu- tion governed by the energy equation of state, ! � p/� < 1/3, to an exterior Schwarzschild vacuum solution at a junction interface. 2 This new emerging picture consisting of a compact object resembling ordinary spacetime, in which the vac- uum energy is much larger than the cosmological vacuum energy, shall be denoted as a dark energy star. 3 We emphasize that the motivation for implementing this generalization arises from the fact that recent observations have confirmed an accel- erated expansion of the Universe, for which energy is a possible candidate. The dynamical stability of the transition layer of these energy stars to linearized spherically symmetric radial perturbations about static equilibrium solutions was