Pani, Paolo and Berti, Emanuele and Cardoso, Vitor and Chen, Yanbei and Norte, Richard (2009) Gravitational wave signatures of the absence of an event horizon: Nonradial oscillations of a thin-shell gravastar. Physical Review D, 80 (12). Art. No. 124047. ISSN 1550-7998 http://resolver.caltech.edu/CaltechAUTHORS:20100120-091912406
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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_s/c ≳ 0.92.
|Additional Information:||© 2009 The American Physical Society. Received 1 September 2009; published 30 December 2009. This work was partially supported by FCT-Portugal through projects PTDC/FIS/64175/2006, PTDC/FIS/ 098025/2008, and PTDC/FIS/098032/2008. Y. C. was supported by NSF Grant Nos. PHY-0653653 and PHY- 0601459, and the David and Barbara Groce Start-up Fund at Caltech. E. B.’s research was supported by NSF Grant No. PHY-0900735.|
|Classification Code:||PACS: 04.30.Db, 04.25.Nx, 04.80.Cc.|
|Official Citation:||Gravitational wave signatures of the absence of an event horizon: Nonradial oscillations of a thin-shell gravastar Paolo Pani, Emanuele Berti, Vitor Cardoso, Yanbei Chen, and Richard Norte, Phys. Rev. D 80, 124047 (2009), DOI:10.1103/PhysRevD.80.124047|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||26 Jan 2010 23:55|
|Last Modified:||26 Dec 2012 11:42|
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