Investigating Rotating Black Holes in Bumblebee Gravity: Insights from EHT Observations

Abstract

The EHT observation revealed event horizon-scale images of the supermassive black holes Sgr A* and M87* and these results are consistent with the shadow of a Kerr black hole as predicted by general relativity. However, Kerr-like rotating black holes in modified gravity theories can not ruled out, as they provide a crucial testing ground for these theories through EHT observations. It motivates us to investigate the Bumblebee theory, a vector-tensor extension of the Einstein-Maxwell theory that permits spontaneous symmetry breaking, resulting in the field acquiring a vacuum expectation value and introducing Lorentz violation. We present rotating black holes within this bumblebee gravity model, which includes an additional parameter $\ell$ alongside the mass $M$ and spin parameter $a$ - namely RBHBG. Unlike the Kerr black hole, an extremal RBHBG, for $\ell<0$, refers to a black hole with angular momentum $a>M$. We derive an analytical formula necessary for the shadow of our rotating black holes, then visualize them with varying parameters $a$ and $\ell$, and also estimate the black hole parameters using shadow observables viz. shadow radius $R_s$, distortion $\delta_s$, shadow area $A$ and oblateness $D$ using two well-known techniques. We find that $\ell$ incrementally increases the shadow size and causes more significant deformation while decreasing the event horizon area. Remarkably, an increase in $\ell$ enlarges the shadow radius irrespective of spin or inclination angle $\theta_0$.