Speaker
Description
We study the general non-equatorial motion of photons in the field of the Kerr and Kerr~de-Sitter spacetimes and using the results of this analysis we propose a classification of these spacetimes, considering the structure of the event horizons, ergosphere and the spherical photon orbits (SPOs), that play crucial role for construction of the light escape cones and related shadows of the central gravitating body. For selected astrophysically relevant classes of the Kerr (-de Sitter) spacetimes we construct and compare the shadows of black holes, naked singularities and superspinars, which we assume to be located between the observer and bright starry background, as they appear for an observer in a different state of motion and with different radial and latitudinal coordinates. The existence of photons with negatively valued energy and their relevance for the radiative Penrose process in the ergoregion is outlined. In the Kerr case, we also mention the existence of a closed stable SPOs in region of possible occurence of thin Keplerian disc and discuss the possibility of some self-occult and self-illumination effects manifesting itself as periodic light echo.
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