Physicists at Columbia University and Adolfo Ibanez University in Chile have found a way to extract energy from a rotating black hole by reconnecting the magnetic field lines near the event horizon. This is reported in an article published in the journal Physical Review D.
Black holes are surrounded by a cloud of charged particles that create a magnetic field inside the ergosphere – the region between the event horizon and the static limit in which the body cannot be at rest. When the lines of force reconnect in the right way, plasma particles can acquire negative energy and fall onto the event horizon. At the same time, other particles accelerated almost to the speed of light leave the vicinity of the black hole, carrying away the rotational energy.
Energy can be extracted with a suitable plasma magnetization and orientation of the reconnecting magnetic field lines. According to scientists, the return of energy from reconnecting the plasma can reach 150 percent, which is explained by the fact that the black hole gives free rotation energy to particles flying away. This process may explain the powerful bursts of radiation in space recorded on Earth.
There are other theoretical ways to extract energy from a black hole. For example, black holes are capable of emitting Hawking quantum mechanical radiation, and Roger Blandford and Roman Znajek have proposed using electromagnetic torque.