Astrophysical environment around a black hole in the braneworld and its optical signatures

Abstract

We investigate the impact of braneworld theory on the astrophysical environment surrounding a black hole. The black hole is sourced by localized matter from the bulk, which could describe both regular and singular (Schwarzschild) black hole. Employing an Einstein cluster description for the environment, we find that the anisotropic nature of the cluster, coupled with finite brane tension, leads to a weakening of gravity due to the quadratic and nonlocal corrections to the effective four-dimensional field equations. Consequently, this effect prevents horizon formation within the environment. Applying current constraints on the brane tension derived from neutron star observations, we demonstrate that this effect is particularly relevant for sub-stellar mass black holes embedded in compact environments. Furthermore, we investigate the optical signatures of finite brane tension in this scenario, specifically focusing on the black hole shadow and Einstein ring radii. We show that the Einstein ring radius decreases with a smaller brane tension, whereas the black hole shadow radius increases--somewhat contradicts the weakening gravity effects. Ultimately, these two observables may jointly serve to constrain the value of the brane tension in a very specific astrophysical scenarios.