The ergosphere is a fascinating region located just outside the event horizon of a rotating black hole (also known as a Kerr black hole). In this area, the intense rotation of the black hole drags the very fabric of spacetime along with it—a phenomenon called frame-dragging.
Unlike the event horizon, the ergosphere is not a point of no return. Objects can, in theory, escape from this region, but they cannot remain stationary relative to distant observers. Due to the rotation, all matter and even light are forced to co-rotate with the black hole to some extent.
This dragging effect opens up the possibility of energy extraction through a process known as the Penrose process, where particles can enter the ergosphere, split, and one part falls into the black hole while the other escapes with more energy than the original.
The ergosphere blurs the boundary between classical physics and exotic relativistic effects, and it highlights how rotation can profoundly influence the structure of spacetime.