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I might be incorrectly mixing up two separate theories - quantum physics and general relativity but from what I've studied, a Kugelblitz is a black hole that is formed from condensing large amounts of high energy light into a small region of space, enough to cause intense curvature of the spacetime to the extent that an event horizon is formed - a black hole.

However, I've also studied that in particle physics, a high enough energy density in a region of space would give rise to particle-antiparticle pairs, and if that energy is light energy, it would produce electron-positron pairs.

My question is, how can one sustain and continue to add enough energy in a region of space in the attempt to form a kugelblitz but before that the high amounts of energy density leads to particle-antiparticle pairs that escape away from the region? And even if the particles don't escape from the region but contribute to the curvature of spacetime, the resulting black hole isn't a Kugelblitz anymore because it isn't formed from curvature produced solely by light energy.

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  • $\begingroup$ isn't kugelblitz a form of lightning consisting of a spherical volume of ionized air? $\endgroup$ – niels nielsen Sep 4 '18 at 8:49
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    $\begingroup$ @nielsnielsen it literally means ball lightning but it's normally taken to mean a concentration of light so intense that it forms a black hole. See the article on Wikipedia for details. $\endgroup$ – John Rennie Sep 4 '18 at 8:51
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    $\begingroup$ got it, just read it, thanks for the reference- consider me disambiguated. -NN $\endgroup$ – niels nielsen Sep 4 '18 at 8:54
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    $\begingroup$ Just because the light might be converted to matter by pair production would not fundamentally alter the fact that the light created a black hole, even if it created some matter in the process. So I'd still say the term "Kugelblitz" is valid (and it sounds cool :-) ). $\endgroup$ – StephenG Sep 4 '18 at 9:25
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    $\begingroup$ Once an event horizon was formed (a black hole exists), there is no way to tell from the outside what is inside or what formed it. This is a result of the no hair theorem. $\endgroup$ – StephenG Sep 4 '18 at 11:18
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You just need to make your black hole very large. The (average) energy density inside a black hole decreases as $1/r_s^2$ so if you make the Schwarzschild radius large enough you can form the black hole without needing EM amplitudes large enough to cause particle production.

Having said this, I don't think anyone is suggesting that you could actually make a kugelblitz. The conditions needed are extreme to a ridiculous extent. The idea is more of a thought experiment. There have been related calculations showing that a black hole could be made from gravitational waves, which are also massless radiation. However as with light this would never happen in practice.

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  • $\begingroup$ Ahh yes, that makes sense, kind of like dodging pair production or working around it by decreasing the energy density at a single region of space but the overall energy density remains the same because the increase in volume is compensated by more amount of light energy in the total volume. $\endgroup$ – Baalateja Kataru Sep 4 '18 at 9:01

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