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Is there any (known? theoretical?) way to destroy a black-hole?

  • "Destroy" means forcing it to disappear - before it evaporates through Hawking radiation.
  • "Disappear" means that it stops being a black-hole: no more event horizon, no more impossibility for light to escape it, etc - it becomes just a "regular" object of mass or loses the mass completely. (i.e. releases its mass to energy or loses its properties in some other way)
  • "Before" means any time before it would fizzle away through Hawking radiation. Even if it's achieved a split-second earlier, it's a win.
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The standard definition of a black hole in classical GR is that it has an event horizon. By that definition, there is no way to convert the stuff that has fallen into the hole to other stuff that can then be observed from infinity. That would just mean that the spacetime never met the definition of being a black hole spacetime.

If you had something that formed a singularity by gravitational collapse, but the singularity was observable from infinity (at any time, even much later), then that might be somewhat like what you're describing, although it wouldn't be a black hole by the standard definition. However, the statement that that doesn't happen is the cosmic censorship conjecture. (What Aslan Monahov's answer describes sounds like the kinds of scenarios that have been cooked up in attempts to find counterexamples to cosmic censorship.)

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In classical general relativity there is black hole area theorem due to Hawking, which states that given reasonable conditions on matter sources (specifically, the null energy condition), the area of event horizon is non-decreasing with time. So, assuming that those conditions hold, we cannot destroy a black hole, but we can e.g. merge it with another black hole, so that instead of two we would only have one larger black hole.

Quantum fields often do violate the null energy condition and so black hole evaporation through Hawking radiation does not contradict this theorem, however for stellar mass black holes the timescales for such evaporation exceed the current age of the Universe by many orders of magnitude.

If such evaporation seems too slow, then it is possible to greatly increase the rate of black hole's mass loss from Hawking radiation. This could be achieved by constructing around the black hole a system that facilitates efficient removal (and subsequent dissipation) of radiative thermal energy from the near horizon region.

The basic principle is well known in thermal engineering: if the heat dissipation is too slow, put in a heat sink or a heat exchanger, but of course there are some subtleties.

Very close to black hole event horizon Hawking radiation has an almost perfect black body spectrum. However by the time this radiation reaches outside observers its spectrum is modified. This is because the gravitational field of a black hole serves as a barrier to radiation propagating from the black hole horizon: it partially transmits radiation and partially reflects it back onto horizon. Moreover, there are near horizon modes of radiation that do not reach the outer region at all. An optical analogue would be the total internal reflection phenomenon, with photon sphere serving as a (smeared) interface between optically dense near horizon (effective) medium and the almost vacuum outer region.

Using the pair creation metaphor, we can say that some of photons that are created at the horizon never escape and are subsequently reabsorbed by the black hole. But what if we can capture those photons before they are reabsorbed and remove their energy by other means, such as through thermal conduction by material of a “heat sink” around the black hole or via some active heat exchange system? Then it would be possible to increase the “thermal output” of the black hole, and the closer to black hole horizon we can capture those photons, the greater the increase would be. Of course, constructing material structure very close to black hole horizon is no small engineering challenge, and in fact there could be some fundamental limitations on how close to the horizon this structure could be, how efficiently it could absorb Hawking radiation quanta and how efficient is the energy transfer within this structure. Overall the black hole mass loss could be greatly increased relative to “unoptimized” Hawking radiation, but those “fundamental limitations” would not allow us to reduce the black hole lifetime arbitrarily.

References

The process of “mining energy from black hole” has been suggested by Unruh & Wald in [$1$]. In [$2$] there is a pop-sci account and a discussion of limitations. Recent paper [$3$] provides an estimate of black hole mass loss increase of $\approx 2 \cdot 10^2$ achieved by a perfectly absorbing screen placed at $\delta r = 10^{-4} r_s$ away from the black hole.

  1. Unruh, W. G., & Wald, R. M. (1983). How to mine energy from a black hole. General Relativity and Gravitation, 15(3), 195-199, doi:10.1007/BF00759206.

  2. Brown, A. (2015). Can We Mine a Black Hole? Scientific American, 312(2), 44-49, free PDF.

  3. Saraswat, K., & Afshordi, N. (2021). Extracting Hawking radiation near the horizon of AdS black holes. Journal of High Energy Physics, 2021(2), 1-47, doi:10.1007/JHEP02(2021)077, arXiv:2003.12676.

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Kerr–Newman metric predicts that event horizon can disappear after increasing the impulse momentum of black hole. But I am not sure that you can increase the rotating of black hole, it's totally true that you can lower it. Or you can bombard hole with enough amount of charge.

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