While almost everyone on the planet has heard of a black hole and has some very basic understanding of what they are, for most people they are a mystery. The terminology is confusing, the equations used to explain them beyond the grasp of most, and it all seems too hard to break down and figure out what is in the middle of one. For anyone that has ever tried to find the answers to what is going on at the center of black holes, here they will find the simple answers.
The somewhat simple definition of a black hole is that it is a region in space created by the implosion of massive stars in which matter collapses upon itself to infinite density creating a space time curvature which is extreme. When this happens a point of no return of sorts is created in which matter basically disappears and nothing including light escapes. Of course that is all theoretical because we cannot actually get to the center of black hole to prove it.
What scientists believe and theorize is that at the center of a black hole is the “singularity.” Again, speaking theoretically, the singularity is infinitely large. What is infinitely large in this case is the curvature of space. Planets and massive stars do bend gravity to a certain degree, but eventually there is a flattening out. In a black hole the bending of gravity is to the extreme – so far beyond what we see planets capable of doing that it creates a curve which never stops curving. The deeper it goes into the black hole, the infinitely larger it becomes.
What happens around the singularity is that everything becomes compressed. Matter collapses becoming more dense. The more dense it becomes the more it collapses in a vicious circle. This happens because the pressure surrounding matter becomes so high it must constantly condense itself in order to fit into an increasingly small space. In theory, at some point, the space matter has to fit into is so tiny it has no dimension.
One way of looking at it is that there is a space which is in theory infinitely large, but everything in it eventually reaches a point of being infinitely small because it has an infinitely high density. It is so overwhelming that at the singularity, space and time cease to exist and all the laws of physics are completely useless. This is where quantum gravity would come into play which is when space and time are separated and cannot be pieced back together again. Then again everything is actually random at the singularity so the possibility for them to re-connect does theoretically exist.
With all of that in mind, the simple answer of what is at the center of a black hole is that it is the singularity. The singularity is there because spacetime has infinite curvature which has infinite gravity. Infinite gravity is so strong it crushes everything to infinite density. So in one place you have an infinite well of everything and nothing at all.