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Let's say we have a reactor that taps into an artificial black hole (kugelblitz-type). What kind of matter would be needed to feed the black hole to sustain it? Would this matter be treated like fuel?

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  • $\begingroup$ I've also asked things about black holes and the biggest problem isn't what you feed it (anything that you can get in there is good) but how you feed it. A small black hole that gives off useful amounts of energy is both incredibly small and all the energy it releases coming from such a small point will also blow any matter AWAY from it rather than suck it in. So you need an array that is accurate enough to hit something smaller than the atoms you fire at it and with enough speed to make it through the immense energy pressure the BH spits out every second. $\endgroup$
    – Demigan
    Dec 23 '19 at 8:23
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It doesn't particularly matter what type of material you throw into a black hole. About the only physical variables of a black hole that affect the outside universe are mass, rotation, and electric charge. There's no such thing as an 'iron' black hole or a 'hydrogen' black hole. In theory, if you're using a black hole for energy generation, you could use it as a perfectly efficient way to dispose of extraordinarily hazardous materials.

However, the kugelblitz poses a different problem altogether. While a black hole is perfectly happy eating raw sewage or radioactive waste, a kugelblitz-style black hole small enough to generate significant energy will have a diameter smaller than that of the atoms you're trying to cram into it - in fact, it will be smaller than the diameter of individual protons. Maybe if a proton hits it dead-on, the kugelblitz will effectively suck it in, but I don't know for sure. If that is the case, then your method of feeding the black hole would be to fire a steady stream of protons directly at it, which would mean that your fuel would be common hydrogen.

More likely, there is no practical means of feeding matter into a kugelblitz-style black hole, which means that the only way to 'recharge' it would be to replicate the conditions that created it: Using several seconds worth of the sun's total energy output to power a gargantuan laser array which focuses all that energy down to a single near-infinitesimally small point. With this in mind, kugelblitzes strike me as being a means of storing vast amounts of power, not producing vast amounts of power.

EDIT: It occurs to me that it might be easier to feed this micro-black hole than I initially thought. As I understand it, a black hole is, theoretically, actually a point of infinite density, and the size I was talking about is actually its event horizon - that is, the perimeter around the black hole where the escape velocity is equal to the speed of light. I mentioned earlier that an atom might be 'sucked' in if it touched the event horizon... and on reflection, that is exactly what would happen. I was thinking of the event horizon as being a hole too small for an atom to fit through, but the instant an atom touches the event horizon, it's doomed.

Also, the gravity of the black hole extends outside the event horizon, and while you wouldn't be able to feel it even standing a few meters away (at least for a black hole of, say, a million metric tons), it will serve to drag matter towards it. The black hole will be giving off a LOT of heat, and the combination of radiation pressure and the vaporization of any nearby matter will keep it from eating planets, but a stream of particles fired at the black hole fast enough to overcome the radiation pressure will hit a point where the gravity will start to overcome the radiation pressure, and be sucked in, requiring less insane accuracy on the part of the feeder. I'm not sure where that point is though, and I suspect that it's still smaller than the diameter of an atom.

Assuming this does work, though, a problem remains with the practicality of feeding a black hole with a single stream of atoms. By my (very rough) calculations, this IS doable, though you'll probably need at least a few dozen particle accelerators pointed at the black hole, firing a constant stream of relatively heavy atoms (iron, perhaps) at several percent of the speed of light.

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    $\begingroup$ Is there another kind of artificial black hole that would be better suited to a reactor? $\endgroup$ Dec 23 '19 at 8:05
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    $\begingroup$ Not to my knowledge. Off the top of my head, I know of one other means to extract energy from a black hole, but it requires the more traditional style of black hole which is several solar masses in size, not suitable for a reactor. $\endgroup$ Dec 23 '19 at 8:13
  • $\begingroup$ You might be able to feed such a black hole with an x-ray or gamma-ray laser of suitably short wavelength and high power, though there's an upper limit to the electrical field strength of a laser before it starts doing pair production from the quantum vacuum. $\endgroup$ Dec 23 '19 at 13:06
  • $\begingroup$ @carsonogen089 if you can make a black hole out of regular matter via some Suitably Advanced implosion technique, you just need to make it big enough that you can feed it. At that point though its lifespan is probably going to be measured in centuries (at a minimum) so there isn't actually much need to feed it in the first place... just keep it until it gets too hazardous, then fire it out into space and admire the fireworks when it finally goes pop. $\endgroup$ Dec 23 '19 at 13:09
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    $\begingroup$ If the incoming particle misses the black hole even by a little bit, wouldn't it enter a highly elliptical (or even hyperbolic) orbit and come back to the feeder? Probably torn to pieces by the tidal forces, and thus, I guess, fulfilling the purpose of generating energy... $\endgroup$
    – Muuski
    Dec 31 '19 at 21:29
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Black holes have no hair, nor they are picky when it comes to feed them: any matter which is subject to gravitational attraction is welcome by them.

And since you are somehow tapping in the Hawking radiation to get energy produced by the black hole, yes, whatever matter you dump into it is basically a fuel.

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Actually, it's very important what you feed the black hole. Yes, you can load whatever you want into a particle accelerator and throw it at the black hole but this will result in the eventual catastrophic destruction of your power station.

Remember, black holes have only three properties: mass, rotation, and charge. Throw atomic nuclei at it and it's going to get a positive charge. A big positive charge that will keep you from feeding it any more nuclei. Once you can't feed it you've got trouble.

The answer is you have to feed it neutrons, or else alternate feeding it hydrogen and electrons.

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  • $\begingroup$ Good point, I didn't think of that. $\endgroup$ Dec 31 '19 at 22:12
  • $\begingroup$ @FlyingLemmingSoup Thank Robert L. Forward, Firefly. $\endgroup$ Dec 31 '19 at 22:49
  • $\begingroup$ It occurs to me that this is actually a very useful property of black holes. If you intend on moving your kugelblitz, then having it be charged means you can use magnetic fields to manipulate it. You just have to regulate its charge to stay at a level you can handle. $\endgroup$ Jan 2 '20 at 6:56
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I beg to disagree with other answers. From black hole's perspective it is indeed doesn't matter what kind of matter it consumes. But if we want our experiment to be clean, we need to feed it exclusively with non-baryonic matter. Otherwise what we have won't be a "kugelblitz-type black hole" by definition.

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  • $\begingroup$ I don't think that the OP meant that the black hole should be fed purely off of energy when he called it a kugelblitz. I think he just meant that it's an artificial micro black hole of appropriate size to serve as a power source, and we're using the term because creating a black hole out of concentrated energy is the least absurdly impractical way we can conceive of doing it. $\endgroup$ Dec 24 '19 at 7:45

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