What process can extract energy from a rotating black hole?

The process that can extract energy from a rotating black hole is the Penrose process. Proposed by Roger Penrose in 1969, it uses the unusual physics of a spinning black hole’s ergosphere, the region outside the event horizon where spacetime is dragged around by the hole’s rotation.

In the classic version, a particle enters the ergosphere and splits into two parts. One fragment falls into the black hole with negative energy relative to a distant observer, while the other escapes with more energy than the original particle carried. The extra energy comes from the black hole’s rotational energy, causing it to spin down slightly.

The Penrose process is different from Hawking radiation, which is a quantum effect associated with black-hole evaporation. It is also distinct from the Blandford–Znajek process, a magnetic-field mechanism that can extract rotational energy and power relativistic jets. Accretion describes matter falling toward a black hole and is not, by itself, the specific extraction process named here.