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GR: Fachverband Gravitation und Relativitätstheorie
GR 20: Relativistische Astrophysik
GR 20.3: Talk
Friday, March 2, 2012, 13:10–13:30, ZHG 002
On spherical lightlike geodesics in the Kerr spacetime — •Volker Perlick — ZARM, Universität Bremen, 28359 Bremen
It is known that the Kerr spacetime admits spherical lightlike geodesics, i.e., lightlike geodesics that stay on a sphere r= constant in standard Boyer-Lindquist coordinates. In this talk I will present pictures that show the region filled by these spherical lightlike geodesics, for the black-hole case (a2 ≤ m2) and for the naked-singularity case (a2 > m2), and I will discuss the relevance of this “photon region” for gravitational lensing. In the second part of the talk I will investigate the behaviour of the photon region under perturbations of the Kerr spacetime and I will discuss, thereupon, the question of how to distinguish strongly naked singularities from weakly naked singularities; this distinction was introduced by Shwetketu Virbhadra for spherically-symmetric and static spacetimes and is generalised here.