Eur. Phys. J. C (2018) 78: 180
https://doi.org/10.1140/epjc/s10052-018-5578-6

Regular Article - Theoretical Physics

Light escape cones in local reference frames of Kerr–de Sitter  black hole spacetimes and related black hole shadows

Faculty of Philosophy and Science, Institute of Physics and Research Centre of Theoretical Physics and Astrophysics, Silesian University in Opava, Bezručovo nám. 13, 746 01, Opava, Czech Republic

^* e-mail: daniel.charbulak@fpf.slu.cz

Received: 15 November 2017
Accepted: 23 January 2018
Published online: 3 March 2018

Abstract

We construct the light escape cones of isotropic spot sources of radiation residing in special classes of reference frames in the Kerr–de Sitter  (KdS) black hole spacetimes, namely in the fundamental class of ‘non-geodesic’ locally non-rotating reference frames (LNRFs), and two classes of ‘geodesic’ frames, the radial geodesic frames (RGFs), both falling and escaping, and the frames related to the circular geodesic orbits (CGFs). We compare the cones constructed in a given position for the LNRFs, RGFs, and CGFs. We have shown that the photons locally counter-rotating relative to LNRFs with positive impact parameter and negative covariant energy are confined to the ergosphere region. Finally, we demonstrate that the light escaping cones govern the shadows of black holes located in front of a radiating screen, as seen by the observers in the considered frames. For shadows related to distant static observers the LNRFs are relevant.