[Confusion]

There is a minimum amount of mass necessary for an object to be able to collapse upon itself and form a black hole, such as a large star does when the outward pressure due to the internal fusion reaction stalls.

However, any amount of mass can (in classical theory) be compressed far enough to obtain a Schwarzschild radius, from which light cannot escape. This has only to do with the density, not the total mass: a very small mass can still cause a large curvature of space, though only in a very small region of space.

[troels]

OK, now that we're already discussing this topic. I just read this quote from Wikipedia:

"""If one accumulates matter at nuclear density (the density of the nucleus of an atom, about 1018 kg/m3; neutron stars also reach this density), such an accumulation would fall within its own Schwarzschild radius at about 3 solar masses and thus would be a stellar black hole."""

I take that to mean that if I wanted to create a black hole of something with less mass than 3 suns, I would have to compress it beyond the density of an atom nucleus? Is this - even in theory - possible to do? Wouldn't you need some kind of "magic wand" (to stick with the articles authors choice of words?)

[pavel_lishin]

I have strep throat and may not be at my best right now, but iirc the chandrasekhar limit is 1.5 solar masses - it's enough to form a black hole because not only is there a lot of mass, but it's also falling into the center, compressing everything further. So one of your "magic wand" options is acceleration, I think.

[Confusion]

Well, that is why I said 'classical theory' :). I have no clue whether QM allows it and I don't think anyone does: that would amount to knowing the true nature of the 'singularity' inside a black hole.

[jules]

So you could say that all point masses (e.g. electrons) are black holes?

What happens if you take a large black hole, and you throw a lot of electrons into it? Does it get an electric field measurable from the outside? If not, how come an electron does have this field?

[lutorm]

An electron is only a point mass in classical electrodynamics, which leads to all kinds of inconsistencies (the self-energy of its field would be infinite, for example.) In quantum mechanics, there is no such thing as a point mass.

But in any case, the answer to your question is yes. Black holes have 3 quantities: mass, angular momentum, and charge. So, yeah, you can charge up a black hole by dropping charges into it and the charge would be visible to the outside.