Harnessing the power of a virtual black hole could create a crazy bomb: ScienceAlert
Black holes are powerful gravitational engines. So you might imagine that there must be a way to extract energy from it if the opportunity arises, and you would be right.
Sure, we can take advantage of all the heat and kinetic energy of a black hole’s accretion disk and its jets, but even if all you have is a black hole in empty space, you can still extract energy from a trick known as the Penrose process.
First proposed by Roger Penrose in 1971, it is a way to extract rotational energy from a black hole. It uses an effect known as frame drag, in which the rotating object twists the nearby space in such a way that the falling object is pulled toward the object slightly along the rotation path.
We have observed the effect near Earth, although it is small. Close to a rotating black hole, the effect could be enormous. So powerful that within a region known as the ergosphere, objects can be pulled around the black hole at speeds faster than light in free space.
Roughly speaking, the Penrose process aims to fly into the atmosphere of a rapidly rotating black hole, and then release a little mass or radiation into the black hole. The resulting rotational kick sends you away from the black hole faster than you are approaching it. The extra energy you get is balanced by slowing down the black hole’s rotation.
This process could theoretically extract up to 20% of the black hole’s mass energy, which is a lot of energy. In comparison, fusing hydrogen into helium produces only about 1% of the mass’s energy.
Of course, theoretical physicists are never satisfied. If you can extract 20% of the energy mass from a black hole, why not get more than that?
This is the focus of recent research, although it should be noted that it focuses on a more abstract idea of a black hole than what we see in the universe.
Simple black holes can be characterized by three things: mass, spin, and electric charge. The black holes we observe contain the first two, but since matter is electrically neutral, not the third. This paper focuses on charged black holes.
Our universe is also expanding and can be roughly described by solving Einstein’s equations known as the de Sitter space. It describes an empty universe with a positive cosmological constant. Anti-de Sitter space (AdS) would be a universe with a negative cosmological constant.
Although AdS does not describe our universe, it allows for some of the mathematical tricks that theorists love, so it is often used to explore the limits of general relativity. This paper specifically looks at a charged black hole in anti-De Sitter space.
Although this study is completely hypothetical, it is interesting as a “what if” scenario. Instead of extracting energy from the black hole’s rotation, researchers are investigating how to extract energy through particle decay using the Bañados-Silk-West (BSW) effect.
Using some type of electromagnetic or physical confinement mirror, particles can reflect back and forth near the event horizon, gaining energy from the black hole until it decays as usable energy.
The problem with this idea, the authors explain, is that this can lead to a runaway effect where the energy of the particles amplifies the energy of the particles in the form of feedback, leading to what is known as a black hole bomb. So if you find yourself building a power plant near a charged black hole in an anti-De Sitter world, tread carefully.
But what is even more interesting is that the authors also considered the case of a charged black hole in an empty anti-De Sitter universe. In this case, energy will also be extracted from the black hole.
Instead of mirrors, the structure of space-time itself would serve as a kind of confinement chamber. So the charged black hole will release energy on its own. It may be similar to Hawking radiation, but in this case it does not depend on quantum gravity. The authors also found that this condition does not lead to a black hole bomb.
As mentioned earlier, none of this applies to real black holes in our universe. As far as we know, the Penrose process is really the best we can do.
But such studies are useful because they reveal the fundamental nature of space and time. Now we know that even in a strange antiverse that we can only imagine, black holes can release energy over time.
This article was originally published by Universe Today. Read the original article.