Researchers from Tianjin University in China have proposed a way to turn tiny black holes into batteries and nuclear reactors. They published their calculations in the peer-reviewed journal Physics Review D.
In their out-there study, Zhan-Feng Mai and Run-Qiu Yang of the Center for Joint Quantum Studies and Department of Physics describe how it could be possible to extract electric energy from the gravitational energy of a so far hypothetical kind of black hole called a Schwarzschild, or primordial, black hole—one that has mass but no spin or electric charge.
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There are a couple of ways theoretically to get energy out of a black hole, they wrote. For example, particles or waves moving around a spinning black hole can be flung away with more energy than they went in with, under certain conditions. Basically, they’re extracting energy from the black hole’s spin.
The problem is, eventually the black hole loses that spinning energy and it wouldn’t be possible to get energy out anymore.
That might not be a problem for the super tiny black holes Mai and Yang describe, since they don’t spin, but instead the black holes don’t have charge and therefore wouldn’t work as a battery.
What the researchers propose is a way to recharge the black hole by feeding it lots of charged alpha particles (ones made through radioactive decay) all with the same mass and charge. Under certain conditions, the gravitational pull of the black hole would outweigh the electric charge that would normally repel particles apart, meaning they’d only get sucked into the black hole and not spat out. This way, the black hole could be recharged several times, but not indefinitely. The whole idea hinges on the black hole being teeny tiny, the size of an atom.
To get energy out, they’d surround the field with a certain kind of electrically-charged field.
The researchers calculated that they could transform a quarter of the mass of the particles they shoot in, into electric energy. That means an efficiency of 25 percent. For comparison, commercially available wind turbines range from 20 to 40 percent efficiency. The black hole could also function like a nuclear reactor, amplifying the natural, energy-releasing process of alpha particles decaying.
There are some supermassive caveats to this work, however. The idea of getting energy out of black holes isn’t new, cosmologist Katie Mack told Motherboard in an interview. “There’s a long tradition in theoretical physics talking about how to extract energy from black holes,” she said. What’s different about this particular paper is that the researchers talk about the tiny primordial black holes.
But Mack, who holds the Hawking Chair in Cosmology and Science Communication at the Perimeter Institute, pointed out several big caveats with this particular presentation of the intriguing theory. Probably the biggest is that scientists haven’t found any evidence that primordial black holes even exist.
What’s more, because of their tiny size and fast-moving speeds, these black holes would be near-impossible to capture to get any of that theorized energy out. “You can’t grab them. You can’t pick them up, you can’t use electric or magnetic fields. They would just move through anything you’d try to capture them with,” Mack said.
That means forget about any practical application. “They’re not really trying to propose a new technology,” she said.
Mai and Yang didn’t respond to a request for comment.
“If there was any application of this, it would be in the form of giving theoretical physicists something to look for to better constrain or discover new physics in the universe,” she said. Even then, Mack questions the theoretical application. “But I can’t say what the authors might have in mind,” she said.
