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Could we harness energy from black holes?:
A remarkable prediction of Einstein's theory of general relativity -- the theory that connects space, time and gravity -- is that rotating black holes have enormous amounts of energy available to be tapped.
[...] [Now] physicists Luca Comisso of Columbia University and Felipe Asenjo of the Universidad Adolfo Ibáñez in Chile have found a new way to extract energy from black holes by breaking and rejoining magnetic field lines near the event horizon, the point at which nothing, not even light, can escape a black hole's gravitational pull.
"Black holes are commonly surrounded by a hot 'soup' of plasma particles that carry a magnetic field," said Comisso. "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 U.S. National Science Foundation-funded research results could allow astronomers to better estimate the spin of black holes and possibly discover a source of energy for the needs of an advanced civilization, Comisso said.
[...] "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."
Journal Reference:
Luca Comisso, Felipe A. Asenjo. Magnetic reconnection as a mechanism for energy extraction from rotating black holes, Physical Review D (DOI: 10.1103/PhysRevD.103.023014)
(Score: 2) by Muad'Dave on Monday January 25 2021, @12:41PM (1 child)
Wouldn't its gravity be exactly that of Phobos? Just because it's concentrated doesn't mean it would increase.
(Score: 2) by Immerman on Monday January 25 2021, @03:19PM
At any given distance you would be correct, but gravity acceleration varies with distance from the center of mass according to the inverse square law: g = G*m/r^2
When we talk about the gravity of a planet, we're talking at the surface - a.k.a. the point of maximum gravity. Fly upwards, and you're getting further away, so gravity diminishes. Dig under the surface and gravity starts diminishing again, since you're also getting pulled upwards by the mass above you.
But since a black hole is far tinier than a normal object of the same mass, you can get far closer. Get 10x closer, and gravity gets 100x stronger. For a small black hole you could enclose it in shells of various sizes, and each shell would have a different surface gravity based on its distance. The closer you got, the stronger the pull would be, and also, the stronger the tidal forces: your feet would be closer than your head, and thus be pulled more strongly.