Gravastar energy conditions revisited
Abstract
We consider the gravastar model where the vacuum phase transition between the de Sitter interior and the Schwarzschild or Schwarzschild de Sitter exterior geometries takes place at a single spherical δ-shell. We derive sharp analytic bounds on the surface compactness (2m/r) that follow from the requirement that the dominant energy condition (DEC) holds at the shell. In the case of Schwarzschild exterior, the highest surface compactness is achieved with the stiff shell in the limit of vanishing (dark) energy density in the interior. In the case of Schwarzschild de Sitter exterior, in addition to the gravastar configurations with the shell under surface pressure, gravastar configurations with vanishing shell pressure (dust shells), as well as configurations with the shell under surface tension, are allowed by the DEC. Respective bounds on the surface compactness are derived for all cases. We also consider the speed of sound on the shell as derived from the requirement that the shell is stable against the radial perturbations. The causality requirement (sound speed not exceeding that of light) further restricts the space of allowed gravastar configurations.
- Publication:
-
Classical and Quantum Gravity
- Pub Date:
- November 2007
- DOI:
- 10.1088/0264-9381/24/22/022
- arXiv:
- arXiv:0707.1636
- Bibcode:
- 2007CQGra..24.5637H
- Keywords:
-
- General Relativity and Quantum Cosmology
- E-Print:
- LaTeX/IOP-style, 16 pages, 2 figures, changes wrt v1: motivation for eq. (6) clarified, several referecnes added (to appear in Class. Quantum Grav.)