Light from Reissner-Nordstrom-de Sitter black holes

TL;DR

This paper derives the null geodesics and shadow characteristics of Reissner-Nordstrom-de Sitter black holes, providing a new method to detect charged black holes via shadow and redshift measurements.

Contribution

It presents the first derivation of spiral null geodesics around the photon sphere in this spacetime and introduces a criterion for detecting charged black holes without peculiar velocities.

Findings

Derived spiral null geodesics around the photon sphere.

Obtained a method to determine black hole shadow and redshift.

Provided a detection criterion for charged black holes.

Abstract

We derive for the first time the form of the spiral null geodesics around the photon sphere of the Reissner-Nordstrom black hole in the de Sitter expanding universe. Moreover, we obtain the principal parameter we need for deriving, according to our method [I. I. Cot\u aescu. {Eur. Phys. J. C.} (2021) 81:32], the black hole shadow and the related redshift as measured by a remote observer situated in the asymptotic zone. We obtain thus a criterion of detecting charged black holes without peculiar velocities when one knows the mass, redshift and the black hole shadow.