While never thinking about it very much I've always pictured the physical mass of a black hole as being a sort of fist-sized super-squashed lump of matter. I'm not talking about the area of space within the event horizon, I mean the actual stuff. The crushed star stuff.
And yet I read something today that tells me that the physical volume of a black hole is zero; literally zero. A singularity.
How can this be? The atoms in the stars and other stuff that contribute to its mass can't have zero volume, can they? How can an atom take up no physical space?