B Do black holes radiate antimatter?

[friend]

The energy to make these particles comes from the black hole mass - even if the particles could fall in they wouldn't change the energy there. And the particles can only leave anyway.

I guess I'm looking for the mechanism that transfers the mass of the BH to the energy of the particles that escape such that the mass of the BH decreases in the process. What do you mean they can only leave? Why can't they go in? Do the particles that would otherwise go inside get reflected back out because it is more dense nearer the BH?

 

[mfb]

There is no meaningful way to assign the mass of a black hole to specific locations in space.

Why can't they go in?

Go in from where? It is the black hole that produces them. What would "go in" even mean?

Imagine a decay process in particle physics: A->B+C. Do you ask if C can "go in" there as well?
Larger black hole -> little bit smaller black hole + photon. Same idea.

 

[friend]

There is no meaningful way to assign the mass of a black hole to specific locations in space.Go in from where? It is the black hole that produces them. What would "go in" even mean?

Imagine a decay process in particle physics: A->B+C. Do you ask if C can "go in" there as well?
Larger black hole -> little bit smaller black hole + photon. Same idea.

So there is just some coupling constant between BH and radiation? You've mentioned that is was because of curved spacetime that particles are produced. Shouldn't we then see the same affect with Unruh radiation? Does the particle horizon of Unruh radiation shrink as particles are produced?

 

[mfb]

So there is just some coupling constant between BH and radiation?

Don't take the analogy to particle physics too far.

Shouldn't we then see the same affect with Unruh radiation?

I don't know which effect you expect to see. The "horizon" for accelerated reference frames doesn't have a radius, mass, or other properties that could change.

 

[litup]

That is a pop-science myth. It is not what actually happens.That is completely wrong.

All the black holes we know are so massive (3+ solar masses) that they only emit electromagnetic radiation with extremely low frequencies. There is a theoretical chance that they emit massive particles, but the probability that any black hole in the observable ever did that in the history of the universe is below 0.000000001%, so why bother.
At 10^-7 solar masses we get a few neutrinos in addition.
At 10^-16 solar masses or 10¹⁴ kg we get some electrons and positrons - in equal amounts for an uncharged black hole. A black hole with this mass has a Schwarzschild radius of just a few hundred femtometers, smaller than an atom.
At 10¹¹ kg we also get pions as the lightest hadrons. A black hole with this mass is smaller than a proton and emits Hawking radiation at a power of a few GW. It still has a lifetime of about a billion years.

Everything emitted will just fly away, matter and antimatter fly away in exactly the same way.

What numbers do you put on the 'extremely low frequencies'? one hertz? That would be low in my book:) Or do you mean IR frequencies? Also do you really mean black holes in your first example of 1/10,000,000 th solar mass? Don't you mean 10 MILLION solar masses. 10^7 and so forth? Well I guess you really mean 10^-7 looking at it closer. Sorry.

So that hypothetical 10^11 Kg black hole would be quite a power source if you could deal with that much mass. It wouldn't do much good as a propulsion system though if you captured it, I suppose since even with no other mass around it and considering the gigawatt to be converted into acceleration, call it generating 2.5 Gw, then 10^11 Kg would be accelerated at 50 milli g's. Not exactly breathtaking, eh. And that is converting that 2.5 Gw 100% into acel. Of course if you had a spacecraft capable of hanging on to that, you would be still getting about 50 milli g's even if the spacecraft massed a million Kg since that would be about 1/100,000 of the mass of the BH...

 

[mfb]

What numbers do you put on the 'extremely low frequencies'?

Of the order of the Schwarzschild radius divided by the speed of light. In other words, the wavelength is of the order of the Schwarzschild radius. One Hertz for very large black holes, low-frequency radio waves for stellar mass black holes.

It wouldn't do much good as a propulsion system though if you captured it, I suppose since even with no other mass around it and considering the gigawatt to be converted into acceleration, call it generating 2.5 Gw, then 10^11 Kg would be accelerated at 50 milli g's.

You cannot convert a power to an acceleration like that.