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Gravastars, hypothetic astrophysical objects, consisting of a dark energycondensate surrounded by a strongly correlated thin shell of anisotropicmatter, have been proposed as an alternative to the standard black hole pictureof general relativity. Observationally distinguishing between astrophysicalblack holes and gravastars is a major challenge for this latter theoreticalmodel. In the context of stationary and axially symmetrical geometries, apossibility of distinguishing gravastars from black holes is through thecomparative study of thin accretion disks around rotating gravastars andKerr-type black holes, respectively. In the present paper, we consideraccretion disks around slowly rotating gravastars, with all the metric tensorcomponents estimated up to the second order in the angular velocity. Due to thedifferences in the exterior geometry, the thermodynamic and electromagneticproperties of the disks (energy flux, temperature distribution and equilibriumradiation spectrum) are different for these two classes of compact objects,consequently giving clear observational signatures. In addition to this, it isalso shown that the conversion efficiency of the accreting mass into radiationis always smaller than the conversion efficiency for black holes, i.e.,gravastars provide a less efficient mechanism for converting mass to radiationthan black holes. Thus, these observational signatures provide the possibilityof clearly distinguishing rotating gravastars from Kerr-type black holes.

Can accretion disk properties distinguish gravastars from black holes?