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GR: Fachverband Gravitation und Relativitätstheorie
GR 5: Black Holes III
GR 5.1: Vortrag
Dienstag, 12. März 2024, 14:45–15:05, HBR 14: HS 2
Light propagation in a plasma on Kerr spacetime — •Volker Perlick1 and Oleg Tsupko1,2 — 1ZARM, University of Bremen, 281359 Bremen — 2Moscow, Russia
Light propagation in a pressure-free non-magnetised plasma on Kerr spacetime is considered, which is a continuation of our previous study [Phys. Rev. D 95, 104003 (2017)]. It is assumed throughout that the plasma density is of the form that allows for the separability of the Hamilton-Jacobi equation for light rays, i.e., for the existence of a Carter constant. We start with studying spherical orbits, which are contained in a coordinate sphere $r = \mathrm{constant}$, and conical orbits, which are contained in a coordinate cone $\vartheta = \mathrm{constant}$. In particular, it is revealed that in the ergoregion in the presence of a plasma there can exist two different spherical light rays propagating through the same point. We demonstrate that, contrary to the vacuum case, circular orbits can exist off the equatorial plane in the domain of outer communication of a Kerr black hole. Considering the light deflection in the equatorial plane, we derive a new exact formula for the deflection angle which has the advantage of being directly applicable to light rays both inside and outside of the ergoregion. The possibility of a non-monotonic behavior of the deflection angle as a function of the impact parameter is demonstrated in the presence of a non-homogeneous plasma. We also add some further comments to our discussion of the black-hole shadow which was the main topic of our previous paper. - For details see arXiv:2311.10615.
Keywords: black hole; gravitational lensing; shadow