How to close a black hole?

Question

HYPOTHETICALLY SPEAKING OF COURSE:

What's the current thinking on the possibility of closing a black hole?

If I were to literally blow up a star 20 times the mass of our sun would that create a black hole? Or does it actually require that the star go supernova to form the black hole? AND if the latter is true...then reversing the effects of the supernova would close a black hole? I know that's a lot of energy but reversing the effects of a supernova should close a black hole correct?

Any information would be appreciated.

Answer 1

Yes, a star 20 times the mass of our sun going supernova would create a black hole.  The formation of the black hole and the supernova are both the result of the star running out of fuel.  You can't reverse the effects of a supernova - it's a non-reversible process according to thermodynamics.  And no, you can't just negate a black hole - pushing all the light and particles and energy back towards the black hole would just make a bigger black hole.

The only way to get rid of one would be to wait for it to evaporate via Hawking radiation, but we're still not sure that even happens.

Answer 2

As far as I know, there is absolutely no way to close a black hole. They can eventually decay, though. For large black holes, a star has to go into a supernova and even that is not a guarantee of a black hole (neutron stars can be formed). Reversing a supernova would require reversing time, and theoretically that can't happen so again, I don't see how you could close a black hole.

But who knows for sure?

Answer 3

well, this is a pretty loaded question. technically anything can become a black hole, even a photon can become a black hole, so a star may not have to go supernova to create a black hole (im no astrophysicist). my best guess would be yes, it does go supernova before creating a black hole. because the only way for a star to create a black hole without going through a normal life cycle would be for it to siphon mass off of another star. this would cause a runaway thermonuclear reaction, much like what happens when a white dwarf gets too close to another star. so before it was able to gain the required mass to collapse into a black hole it would explode in a supernova because of all that mass being added on.

and there is no way to reverse a supernova once it has become a black hole without completely reversing time itself, which isnt possible in my opinion. see, a black hole is black because not even light itself can escape. so to reverse a supernova you would have to make matter travel faster than light. FTL travel is impossible. as an object accelerates it gains mass. at the speed of light mass becomes infinite, so traveling at or above the speed of light is highly impossible.

and im not even sure if traveling faster than light would get you out of a black hole. because inside of a black hole time stops, which is why light cant escape. so dont think it actually has anything to do with the speed of the object trying to escape the black hole.

but "closing" a black hole is possible. not artificially of course, but black holes evaporate away after tens, if not hundreds of billions of years. see, a property of spacetime is that whats called virtual particle pairs create themselves out of nothing. they are called "virtual particle pairs" because they do not last very long. they are a particle antiparticle pair, so once they are created they annihilate eachother. so overall the conservation of energy is maintained. it is possible for the pair to be created on the event horizon, or boundary, of a black hole. if this were to happen one particle could fall in, while the other falls away from the black hole. this would appear to an outside observer that the black hole emitted a particle, in order to maintain conservation of energy. so the black hole loses mass.