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Nothing can escape a black hole once it has crossed its event horizon but mathematical analysis over the last several decades has shown that there are ways to extract energy from a rotating black hole. Researchers have now revealed new work presenting an innovative way to harness energy out of a black hole, publishing their findings in Physical Review D.
Mathematically speaking, if a black hole rotates then it has an ergosphere. This is a region outside its event horizon (the threshold where to escape the pull of the black hole you’d need to move faster than the speed of light) where it is theoretically possible to steal some of the black hole's energy. Stephen Hawking worked out ways that quantum mechanics can remove energy from black holes. Nobel physicist Roger Penrose has a more mechanical approach that requires following particular orbits. The new work focuses on magnetic fields.
The magnetic fields of complex objects often exhibit the repeated breaking and rejoining of magnetic field lines. This is seen on the Sun for example, with spectacular releases of energy. Researchers believe that this could be the case for black holes too. The right magnetic interaction could accelerate particles away from the black hole, removing some of its energy.
"Black holes are commonly surrounded by a hot 'soup' of plasma particles that carry a magnetic field," Luca Comisso from Columbia University said in a statement. "Our theory shows that when magnetic field lines disconnect and reconnect, in just the right way, they can accelerate plasma particles to negative energies and large amounts of black hole energy can be extracted."
The sci-fi reason why this is exciting is that by getting energy from a black hole, you are getting a lot more energy out compared to the energy supplied. The team estimates that the process could have an efficiency of up to 150 percent, something that is unachievable on Earth. So an advanced alien civilization could decide to use a black hole as an incredible power station if it had the know-how.
The scientific reason it's exciting is that this process might already happen in nature, without the help of intelligent aliens. There are several phenomena surrounding black holes that are not fully understood, such as black hole flares that can be detected from Earth, so it is possible that magnetic reconnection in the ergosphere could help explain what we see.
"Our increased knowledge of how magnetic reconnection occurs in the vicinity of the black hole might be crucial for guiding our interpretation of current and future telescope observations of black holes, such as the ones by the Event Horizon Telescope," said co-author Felipe Asenjo from Universidad Adolfo Ibanez in Chile.
Perhaps in the future, mining energy from black holes could be the answer to our power needs.
"Thousands or millions of years from now, humanity might be able to survive around a black hole without harnessing energy from stars," Comisso said. "It is essentially a technological problem. If we look at the physics, there is nothing that prevents it."
