Inside a black hole, nothing can hold together. At the "event horizon" then SOMETHING traveling the speed of light can stay there, anything else falls in further. But within the black hole, even light collapses to the center and can't escape.

So there is no surface, you just keep falling and falling. Anything whether stationary or moving, even a light beam moving at the speed of light away from the center, is still on an inevitable trajectory towards the center of the black hole.

However for really big black holes, then crossing the event horizon can be quite a gentle process. You are doomed at that point, there, is no way you can GET back out again, but you don't notice it for a while later

Example here BLACK HOLES by Ted Bunnwhere he says that if you started, say, from a distance of ten times the black hole's radius, for a MILLION solar mass black hole, then it WOULD take 8 minutes to reach the horizon, and then, only another seven seconds to hit the singularity at the center. But you'd survive for a short while over the horizon.

For a truly gigantic super cluster of galaxies mass black hole, then you could fall for some TIME before you hit the center.

As to what is in the center - well it's a mathematical point. So it is theoretically of no size at all. Everything just ends up being a single point.

I hope help u