Can we harness energy from black holes?

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A remarkable prediction of Einstein’s general theory of relativity – the theory that connects space, time and gravity – is that rotating black holes have enormous amounts of energy available to tap.

For the past 50 years, scientists have been trying to come up with methods to unleash this power. Nobel physicist Roger Penrose theorized that a particle-particle energy can draw energy from a black hole; Stephen Hawking proposed that black holes can release energy through quantum mechanical emission; while Roger Blandford and Roman Znajek proposed electromagnetic torque as a major means of extracting energy.

Now, in a study published in the journal Physical overview D, physicists Luca Comisso of Columbia University and Felipe Asenjo of Universidad Adolfo Ibanez in Chile, found a new way to extract energy from black holes by breaking magnetic field lines and rejoining them, the point from which nothing, and not even light, can escape the black hole’s gravity.

“Black holes are usually surrounded by a hot ‘soup’ of plasma particles carrying a magnetic field,” said Luca Comisso, a research scientist at Columbia University and first author of the study.

“Our theory shows that when magnetic field lines are properly disconnected and reconnected, it can accelerate plasma particles to negative energies and large amounts of black hole energy can be extracted.”

This finding could enable astronomers to better estimate the turn of black holes, drive the release of black holes, and could even provide a source of energy for the needs of an advanced civilization, Comisso said.

Comisso and Asenjo based their theory on the premise that the reconnection of magnetic fields accelerates the plasma particles in two different directions. One plasma flow is forced against the turn of the black hole, while the other is driven in the direction of the turn and the claws of the black hole can escape, releasing force as the plasma swallowed by the black hole, negative energy has.

“It’s like someone can lose weight by eating candy with negative calories,” says Comisso, who explained that a black hole actually loses energy by eating particles with negative energy. “It may sound strange,” he said, “but it can happen in a region called the ergosphere, where the space-time continuum rotates so fast that each object rotates in the same direction as the black hole.”

Within the ergosphere, magnetic reconnection is so extreme that the plasma particles accelerate to speeds approaching the speed of light.

Asenjo, professor of physics at the Universidad Adolfo Ibáñez and co-author of the study, explained that the high relative velocity between captured and escaping plasma currents makes it possible to extract massive amounts of energy from the black hole in the proposed process.

“We have calculated that the process of plasma energy can achieve an efficiency of 150 percent, much higher than any power plant operating on earth,” Asenjo said. “Achieving an efficiency of more than 100 percent is possible because black holes leak energy, which is given away for free to the plasma escaping from the black hole.”

The process of energy extraction envisaged by Comisso and Asenjo can already work in a large number of black holes. This is perhaps the cause of black hole torches – powerful bursts of radiation that can be detected from the earth.

“Our increased knowledge of how magnetic reconnection occurs in the vicinity of the black hole can be crucial to the interpretation of current and future telescope observations of black holes, such as those through the Event Horizon Telescope,” said Asenjo.

Although it sounds like the stuff of science fiction, extracting energy from black holes may be the answer to our future power needs.

“Thousands or millions of years from now, humanity may be able to survive over a black hole without harnessing the energy of stars,” Comisso said. “It’s essentially a technological problem. If we look at physics, there’s nothing stopping it.”

The study, Magnetic Connection as a Mechanism for Extracting Energy from Rotating Black Holes, was funded by the Windows Science on the Universe Initiative, NASA, and the National Fund for Scientific and Technological Development of Chile.

Vyacheslav (Slava) Lukin, a program director at NSF, said the Foundation intends to catalyze new theoretical efforts based on frontier observations at facilities such as the EHT, which bring together theoretical physics and observational metrics under one roof.

“We look forward to the possible translation of seemingly esoteric studies of black hole astrophysics into practice,” Lukin said.

“The ideas and concepts discussed in this work are truly fascinating,” said Vyacheslav (Slava) Lukin, program director of the National Science Foundation. He said NSF aims to catalyze new theoretical efforts based on frontier observations, and to bring theoretical physics and observational expertise under one roof.

“We are looking forward to the possible translation of seemingly esoteric studies of black hole astrophysics into the practical field,” he added.