Who proposed the Penrose process for extracting energy from a rotating black hole?

Roger Penrose proposed the Penrose process for extracting energy from a rotating black hole.

Penrose introduced the idea in 1969 while studying the ergosphere of a Kerr black hole. In the thought experiment, an object enters the ergosphere and splits into two parts. One part falls into the black hole with negative energy as measured from far away, while the other escapes with more energy than the original object had. The extra energy comes from the black hole’s rotation.

The process cannot operate around a nonrotating Schwarzschild black hole because it depends on the ergosphere. Theoretically, repeated extraction could reduce the black hole’s spin, although practical astrophysical mechanisms are more likely to involve magnetic fields and plasma. Penrose’s work also helped establish that rotating black holes can act as energy reservoirs.