Shadow analysis for rotating black holes in the presence of plasma for an expanding universe

TL;DR

This paper derives an analytic formula for the shadow boundary of a Kerr-de Sitter black hole surrounded by plasma in an expanding universe, analyzing how plasma affects the shadow's shape and size.

Contribution

It introduces a new analytic approach to determine black hole shadows in plasma-filled, expanding universe environments, extending previous models.

Findings

Derived an explicit formula for the shadow boundary in plasma environments.

Analyzed the impact of plasma on shadow size and shape.

Compared shadow curvature with and without plasma.

Abstract

We explore the structure of shadow for a Kerr-de Sitter black hole with a non-magnetized, pressureless plasma surrounding it. Specific plasma distributions are considered to separate the Hamilton-Jacobi equation and find the photon regions. An analytic formula describing the boundary curve of the shadow for such a black hole in an expanding universe for an observer at any finite point outside the horizon is derived. We observe deviations which are further explored by calculating the curvature radius at a particular point for such structures in the presence and absence of plasma and calculate the diameter of the shadow.