We don't anything about black holes themselves. Only that they are very heavy and only the effects they have on their surroundings. Yes, we see a lot of things, but those things are caused by the black hole but are not inherent to the black hole. Since we cannot look into the black hole, neither any information comes from it, it all remain speculative. Only mathematics and physics can tell us sort of what would be going inside a black hole, but even they brake under the black hole's conditions. The only thing we know a black hole is the remnant of a very massive star (or multiple stars), in which it's core had no fusion energy left to withstand the power of gravity and the whole thing collapsed into itself. Whether this core has still an actual dimension is up to debate. If you look at it pure chemistry wise, then you have to try to imagine if it is possible to even squeeze quark particles into each other. I have no idea. If yes, then the core is infinite small, if not, then the core might be the size of a football.