Speaker
Description
Black holes can connect different regions of spacetime: in the Kerr solution, geodesics may pass through or around the ring singularity without destruction. Although perturbations are thought to destabilize such passages by generating additional singularities, their possible existence has direct observational consequences. We show that if Sgr A or M87 is described by the maximally extended Kerr geometry, the Event Horizon Telescope (EHT) could detect photons originating from a second asymptotic region or the Cauchy horizon. Such photons would appear to emerge into our universe from within the black hole shadow. Tracing light rays in the extended Kerr spacetime defines a map between the observers image plane and the source-sky of the photons. Features of this map provide observational templates for searches in current and future EHT data, offering a direct test of whether astrophysical black holes realize the global Kerr extension or whether the Cauchy horizon instability precludes such passages.