On negative-phase-velocity propagation in the ergosphere of a charged rotating black hole

After adopting a noncovariant approach, we found that the propensity of a rotating black hole to support the propagation of electromagnetic plane waves with negative-phase-velocity (NPV) in its ergosphere is highly sensitive to the presence of charge. The change in shape and size of the ergosphere induced by increasing the black hole's charge gives rise to increased possibilities for NPV propagation. At a fixed ergosphere surface, increasing the black hole's charge concentrates the NPV-supporting regions towards the ergosphere's equator.