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My question is a hypothetical: if I were to create a black hole the size of a family house, in New York, is there any way that it can be stopped, or interrupted? If a black hole of this size is formed, will everyone die?

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  • $\begingroup$ An event horizon cannot be scaled back down. You could try and prevent more matter from falling into it. But what's already in there, is there forever. It will slowly evaporate via Hawking radiation over trillions and trillions of years. $\endgroup$ – Florin Andrei Jul 29 at 19:21
  • $\begingroup$ OMG, that would be a big Oops. Right there at that moment I assume everything nearby will be sucked in. How would you prevent other things from falling in? $\endgroup$ – Logikal Jul 29 at 19:24
  • $\begingroup$ Move things as far away as possible? Sweep the vicinity of objects orbiting it? A lot of that would be very hard to do, requiring lots and lots of energy. TBH, the stuff that's pretty close to the event horizon is pretty much gone from a practical perspective. Extracting things from that gravitational well is extremely expensive from an energy perspective. $\endgroup$ – Florin Andrei Jul 29 at 19:28
  • $\begingroup$ I’m not sure how big family homes are around there, but a black hole with radius of 10 meters (about 30 ft) is going to be already a thousand times heavier than the Earth. Having any object of that size - black hole or not - in your lab on Earth would probably get us all killed. $\endgroup$ – tuomas Jul 29 at 20:09
  • $\begingroup$ @Logikal not quite thousands as the radius to mass ratio is 1 to 1. Earth's Schwarzschild radius is about .35 inches. A thousand of those, 350 inches or just under 9 meters. A house sized black hole - the mass of 4 Jupiters. It would still destroy the Earth with little trouble. Even on the far side of the planet the gravitational and/or tidal forces would be visibly disruptive in less than a second. I love mad scientists and their experiments. $\endgroup$ – userLTK Jul 30 at 3:31
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Your black hole is quite massive. It has a mass that is much greater than the mass of the Earth, (about 1000 times the mass of the Earth. And the rest of the Earth isn't moving very fast relative to the black hole. So in a short amount of time everything falls into the black hole. This will be a quite energetic process with a lot of high intensity radiation being given off. But in short "everybody dies" and quite quickly too.

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No. Only effect that might reverse the formation of a black hole is Hawking radiation. For Hawking radiation to actually reduce the size of black hole, the temperature of the BH must be less than the temperature of its environment, because otherwise it will absorb more energy from the heat of the environment than it’ll radiate away, and thus become bigger over time even if it doesn’t suck any material in.

For a black hole to be cooler than space around Earth would require a black hole size of just few micrometers, way smaller than your house-sized black hole (which, by the way, is going to be several magnitudes heavier than the whole Earth; Earth, if turned into a BH, would have a radius of about 3 cm or an inch).

Also, even if your black hole was smaller, it would cause some pretty intense radiation while evaporating, which might kill us all - this really depends on the size, but mass tends to have a lot of energy after all.

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  • $\begingroup$ It basically ends with what looks like an explosion, due to the accelerated nature of the Hawking evaporation. And it's a very big "explosion", too. $\endgroup$ – Florin Andrei Jul 29 at 21:02
  • $\begingroup$ If the size of this black hole is over few picometers, evaporation will provide more energy than gravitational binding energy of the Earth. And that sure is a bad thing. Don’t try this at home! $\endgroup$ – tuomas Jul 29 at 21:08

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