A black hole is like a whirlpool in a river: anything that falls in can never escape. But it also has an outer zone, the ergosphere, where space itself moves faster than light and drags any object along. Usually, the size of this zone is tightly linked to the hole's mass and spin rate.
In the new work, scientists considered a black hole with a hidden fifth dimension — tiny and curled into a ring. If you give the hole a kick along this ring, in our four-dimensional world it looks like the appearance of an electric charge. But the most curious part: the hole's horizon: its 'point of no return'—remains unchanged, while the ergosphere inflates like a balloon blown up from an invisible dimension.
This result matters for the search for signs of extra dimensions in real black holes. If we ever manage to measure the ergosphere's size around a rapidly spinning hole, a discrepancy with calculations would point to the influence of higher dimensions. For now, the work reminds us that even the most familiar cosmic objects may harbor entire worlds within.
The ergosphere is the region around a rotating black hole where any object is forced to rotate with the hole, even if it tries to stay still. You can still escape from it, but only by sacrificing some energy.
In the movie 'Interstellar,' the characters use the ergosphere of a supermassive black hole for a maneuver that lets them shed excess mass and escape the gravitational trap.