Shadows of black hole surrounded by anisotropic fluid in Rastall theory

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 psi. It encompasses, as special cases, Kerr (N-s -> 0) and Kerr-Newman (s = 0 and N-s = -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 (r(O), theta(O)) in the domain [r(+), r(q)]. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

Due to the gravitational lensing effect, a black hole projects a shadow larger than its horizon over a bright background, and the shape and size can be calculated. The first direct image of a black hole produced by the Event Horizon Telescope collaboration is consistent with the shadow of a Kerr black hole according to general relativity. Deviations from the Kerr black hole due to modified theories of gravity are important for testing these theories through astrophysical observation.