Black hole shadow to probe modified gravity

Abstract

We study the black hole’s shadow for Schwarzschild–de Sitter and Kerr–de Sitter metrics with the contribution of the cosmological constant Λ. Based on the reported parameters of the M87* black hole shadow, we obtain constraints for the Λ and show the agreement with the cosmological data. It is shown that the coupling of the Λ-term with the spin parameter reveals peculiarities for the photon spheres and hence for the shadows. Within the parametrized post-Newtonian formalism, the constraint for the corresponding Λ-determined parameter is obtained.