Abstract:
Due to the gravitational lensing effect, a black hole casts a shadow larger than its horizon over a bright
background, and the shape and size can be calculated. The Event Horizon Telescope collaboration has
produced the first direct image (shadow) of the black hole and it is in accordance with the shadow of a
Kerr black hole of general relativity. However deviations from the Kerr black hole arising from modified
theories of gravity are not ruled out and they are important as they offer an arena to test these theories
through astrophysical observation. This stimulates us to investigate rotating black holes surrounded
by anisotropic fluid in Rastall theory namely a rotating Rastall black hole, which are characterized by
mass M, spin a, field structure parameter Ns and the Rastall parameter ψ. It encompasses, as special
cases, Kerr (Ns → 0) and Kerr–Newman (s = 0 and Ns = −Q
2
) black holes. The rotating Rastall black
hole is characterized by an additional cosmological-like horizon apart from Cauchy and event horizons.
We derive an analytical formula for the shadow of a rotating Rastall black hole and go on to visualize
the shadow of black holes for various values of the parameters for an observer at a given coordinates
(rO, θO) in the domain [r+,rq].
