Gravitational wave signatures of the absence of an event horizon: Nonradial oscillations of a thin-shell gravastar
- Dipartimento di Fisica, Universita di Cagliari, and INFN sezione di Cagliari, Cittadella Universitaria 09042 Monserrato (Italy)
- Department of Physics and Astronomy, The University of Mississippi, University, Mississippi 38677-1848 (United States)
- Theoretical Astrophysics 350-17, California Institute of Technology, Pasadena, California 91125 (United States)
Gravitational waves from compact objects provide information about their structure, probing deep into strong-gravity regions. Here we illustrate how the presence or absence of an event horizon can produce qualitative differences in the gravitational waves emitted by ultracompact objects. In order to set up a straw-man ultracompact object with no event horizon, but which is otherwise almost identical to a black hole, we consider a nonrotating thin-shell model inspired by Mazur and Mottola's gravastar, which has a Schwarzschild exterior, a de Sitter interior and an infinitely thin shell with finite tension separating the two regions. As viewed from the external space-time, the shell can be located arbitrarily close to the Schwarzschild radius, so a gravastar might seem indistinguishable from a black hole when tests are only performed on its external metric. We study the linearized dynamics of the system, and, in particular, the junction conditions connecting internal and external gravitational perturbations. As a first application of the formalism we compute polar and axial oscillation modes of a thin-shell gravastar. We show that the quasinormal mode spectrum is completely different from that of a black hole, even in the limit when the surface redshift becomes infinite. Polar quasinormal modes depend on the equation of state of matter on the shell and can be used to distinguish between different gravastar models. Our calculations suggest that low-compactness gravastars could be unstable when the sound speed on the shell v{sub s}/c > or approx. 0.92.
- OSTI ID:
- 21316547
- Journal Information:
- Physical Review. D, Particles Fields, Vol. 80, Issue 12; Other Information: DOI: 10.1103/PhysRevD.80.124047; (c) 2009 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 0556-2821
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COSMOLOGY AND ASTRONOMY
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
BLACK HOLES
DE SITTER SPACE
DISTURBANCES
EQUATIONS OF STATE
GRAVITATION
GRAVITATIONAL WAVES
METRICS
OSCILLATION MODES
OSCILLATIONS
PERTURBATION THEORY
RED SHIFT
SCHWARZSCHILD RADIUS
SHELL MODELS
SOUND WAVES
SPACE-TIME
SPECTRA
SURFACES
VELOCITY