Our Universe behaves like a stretched elastic sheet: massive bodies dent it, creating spacetime curvature — gravity. In brane-world theory, a hidden dimension is added, and this sheet becomes just a surface in a higher-dimensional space. The brane tension determines how much the sheet dents: the weaker the tension, the weaker the gravity.
Scientists have studied how this affects black holes of the Schwarzschild type, surrounded by a dense cloud of particles. For light holes (less than a star's mass), the weakened gravity might not form a horizon — the boundary from which nothing can escape. Constraints on brane tension come from observations of neutron stars.
An unexpected effect: the black hole's shadow grows while the Einstein ring — the luminous halo around it — shrinks. Measuring these two parameters could reveal the presence of extra dimensions.
as written by the authors arXiv:2605.26124
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.
If brane tension disappeared, our Universe would become completely flat and devoid of gravity.
In the film *Interstellar*, highly advanced beings live in five dimensions — much like the brane idea from scientific theories.