## Key takeaways

- The Penrose process allows for the extraction of rotational energy from black holes using the concept of frame dragging.
- Objects in the ergosphere of a spinning black hole can be accelerated to speeds faster than light in empty space, making energy extraction possible.
- The Penrose process can theoretically convert up to 20% of a black hole’s mass energy into usable energy, much higher than nuclear fusion.
- Recent theoretical studies explore energy extraction from charged black holes in an anti-de Sitter (AdS) universe, leading to potential “black hole bombs.”
- These theoretical explorations, while not applicable to our universe, help reveal fundamental truths about space, time, and black hole behavior.

Black holes are very strong gravitational engines. So you may think that if given the opportunity, there must be a method to extract energy from them, and you would be correct.

Certainly, we could harness all of the heat and kinetic energy of a black hole’s accretion disk and jets, but even if all you had was a black hole in space, you could extract energy via a method known as the Penrose process.

Roger Penrose first proposed it in 1971 as a method of extracting rotational energy from a black hole. It employs a technique known as frame dragging, in which a rotating body bends adjacent space so that an item falling towards the body is pulled somewhat along the direction of rotation.

We have seen the impact near Earth, but it is small. The effect around a revolving black hole can be enormous. So powerful that items in a zone known as the ergosphere can be pulled around the black hole at speeds faster than light in empty space.

The Penrose process is roughly defined as flying toward the ergosphere of a rapidly spinning black hole and then releasing a little amount of mass or radiation into it. The resultant rotating kick propels you away from the black hole quicker than you approached it. The more energy you gain is offset by delaying the black hole’s spin.

This process may theoretically extract up to 20% of the black hole’s mass energy, which is enormous. In comparison, fusing hydrogen into helium produces just approximately one percent of the mass energy.

Of course, theoretical physicists are never content. If you can get 20% of the mass energy from a black hole, why not more?

This is the subject of a recent research, albeit it should be highlighted that it deals with a more abstract concept of a black hole than what we experience in the Universe.

Simple black holes may be distinguished by three characteristics: mass, spin, and charge. The first two are present in the black holes we witness, but the third is absent since matter is electrically neutral. This paper discusses charged black holes.

Our Universe is also growing, and it may be approximately characterized using a solution to Einstein’s equations known as de Sitter space. It refers to an empty world with a positive cosmological constant. Anti-de Sitter space (AdS) refers to a universe having a negative cosmological constant.

Although AdS does not explain our Universe, it does allow for some mathematical tricks that theorists like, therefore it is frequently employed to test the limitations of general relativity. This research explicitly examines a charged black hole in anti-de Sitter space.

Although this study is completely hypothetical, it is intriguing as a “what-if” situation. The scientists propose exploiting the Bañados-Silk-West (BSW) phenomenon to harvest energy from particle disintegration, rather than relying on black hole spinning.

Using electromagnetic or physical confinement mirrors, particles can be bounced back and forth near the event horizon, receiving energy from the black hole before decaying into useful energy.

The authors demonstrate that this approach can lead to a runaway process in which particle energy amplifies particle energy in a feedback loop, resulting in 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 universe, use caution.

More interestingly, the authors examined the situation of a charged black hole in an otherwise empty anti-de Sitter universe. In this scenario, energy would be collected from the black hole.

Instead of mirrors, the structure of space-time would function as a type of confinement chamber. So the charged black hole would emit energy on its own. It would be analogous to Hawking radiation, except it would not depend on quantum gravity. The authors also discovered that this circumstance does not result in a black hole bomb.

As previously stated, none of this pertains to actual black holes in our Universe. As far as we know, the Penrose procedure is the best we could possibly achieve.

However, these investigations are helpful because they disclose fundamental truths about the nature of space and time. And now we know that black holes may release energy over time, even in bizarre anti-universes that we can only fathom.

This article was originally published by Universe Today. Read the original article.