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

Understand

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.