Given how much rotating black hole differs from non-rotating one I believe a black hole consisting exclusively of swirling photons could have some very unique properties that out best models don't necessarily capture.

For example some resonances that could expell enough energy through gravitational waves to make it unstable and explode into a version of a big bang.

But it's charge would be negated, since charge is one of the parameters, no? Not sure it affects anything tho.

Not necessarily. You could load up one black hole with electrons and the other black hole with anti-protons ... both would have negative charge, -Q ... but the latter would have a much greater mass, since anti-protons are much heavier than electrons, despite having equal charges.

"Antimatter" is really only "anti" in a few respects. First, the lepton or baryon number has the sign flipped. An electron has a positive lepton number; a positron would have a negative lepton number. The charges are also flipped, where applicable (anti-neutrons still have a charge of zero). Isospin is flipped; spin is not. Mass is not, in three ways.

First, if you converted an anti-proton into pure energy (ignoring charge conservation, et al), it is the same energy as you would get out of a proton.

Second, an anti-proton exerts the same gravitational pull as a proton. A world of anti-matter would cause you to fall toward it the same way the Earth would.

Third, a force exerted on an antiproton causes it to accelerate along the same vector as the force, so the inertia is the same as regular matter.

People have theorized, myself included, on what some kind of matter where mass was negative (let's dub it nega-matter) would look like, which is to say that a force pushing it away would contrarily draw it toward you. You can simulate it in particle life, likely, but what would happens is that all of the nega-electrons would feel electrostatic repulsion and therefore clump together, as would all of the nega-protons. These two lumps of enormous charge (we just don't get that in real life, electrostatics are dozens of orders of magnitude more powerful than gravity) would create an "attractive" field between them of nearly incalculable strength and, because they would move opposite to the vector of the force, promptly zoom away at many nines of the speed of light. In short, they would sort themselves out and fly away to distant corners of the universe with great haste.

> would be indistinguishable from a black hole fed entirely by the equivalent matter

> one black hole with electrons and the other black hole with anti-protons

But electrons and anti-protons are not equivalent. Positrons are.

That's what I meant -- if the same energy of electrons and positrons are used, the black holes would not be indistinguishable, their charges would be different.

Oh, I see what you're getting at. Yes, the Q would be flipped. M, though, stays the same.

Sometimes I think the "anti-" prefix has done more harm than good to communicate what's going, like the choice of assigning "negative" to electrons.

What is charge in this context? Photons can’t leave the black hole, so this charge as good as lost?

Well, if you load up a black hole with, say, electrons, it will have an electrical field similar to a point charge -Q, just the way the mass M behaves as a point mass emitting a gravitational field (or distortion in spacetime, take your pick).

Additionally, when you get Hawking radiation into the mix, negatively-charged particles (electrons, muons, tauons ... but probably mostly electrons) would be preferentially emitted, since pair production near the horizon would preferentially eject the negative particle via electrostatic repulsion and just as preferentially recapture the positive member of the pair.

Not that you asked, but the angular momentum looks different than the other two, it actually changes the shape of the event horizon to something more oblate.