Appearance of Keplerian discs orbiting Kerr superspinars
Abstract
We study optical phenomena related to the appearance of Keplerian accretion discs orbiting Kerr superspinars predicted by string theory. The superspinar exterior is described by standard Kerr naked singularity geometry breaking the black hole limit on the internal angular momentum (spin). We construct local photon escape cones for a variety of orbiting sources that enable us to determine the superspinars silhouette in the case of distant observers. We show that the superspinar silhouette depends strongly on the assumed edge where the external Kerr spacetime is joined to the internal spacetime governed by string theory and significantly differs from the black hole silhouette. The appearance of the accretion disc is strongly dependent on the value of the superspinar spin in both their shape and frequency shift profile. Apparent extension of the disc grows significantly with the growing spin, while the frequency shift grows with the descending spin. This behaviour differs substantially from the appearance of discs orbiting black holes enabling thus, at least in principle, to distinguish clearly the Kerr superspinars and black holes. In vicinity of a Kerr superspinar the nonescaped photons have to be separated to those captured by the superspinar and those being trapped in its strong gravitational field leading to selfillumination of the disc that could even influence its structure and cause selfreflection effect of radiation of the disc. The amount of trapped photons grows with descending superspinar spin. We thus can expect significant selfillumination effects in the field of Kerr superspinars with nearextreme spin a ~ 1.
 Publication:

Classical and Quantum Gravity
 Pub Date:
 November 2010
 DOI:
 10.1088/02649381/27/21/215017
 arXiv:
 arXiv:1101.3569
 Bibcode:
 2010CQGra..27u5017S
 Keywords:

 General Relativity and Quantum Cosmology
 EPrint:
 accepted in Classical and Quantum Gravity (September 1st, 2010)