My understanding of general relativity is rudimentary at best, so bare with me and correct me where necessary. Also, any math in the explanation is appreciated, but try to also keep the answer intuitive for rookies like myself :)
The short version:
Aren't black holes just neutron\quark stars compressed at least slightly beyond the associated Swartzschild radius?
The long version:
Per my understanding of general relativity, if I were to replace a star with an equally massive black hole, I should find that the space-time curvature from the boundary of where the star's surface used to be and beyond should stay the same, and I should also find that the space-time in the region between said boundary and the event horizon should continue to curve such that the curvature is continuous at the boundary. If I continue to probe\calculate the curvature up until the center of mass, I should find that it grows to infinity, but why should I be able to do so without running into any spatial boundary?
Consider neutron or quark stars stars (if the latter exist), where degeneracy pressure prevent the matter from compressing any further. It is also the case that if such star would cross a certain mass threshold, then the Swartzschild radius would become bigger than the radius of the star, thus resulting in a black hole.
So the intuition I get is that it would be fair to assume that when a core of a star is massive enough to collapse into a black hole, we should still expect to find all its mass compressed as much as the degeneracy pressure would allow it - we just wouldn't be able to observe it since that mass is enclosed within the event horizon. This would also imply that asking what is the space-time curvature at the center of mass (where the result is infinity) is meaningless, since the degenerate mass poses a spatial boundary, beyond which one cannot probe the curvature.
Is that reasonable? Are there any holes in my intuition? I'm mostly curious about that scenario because I never hear physicists talk about it (and I assume there's a reason:).
Bonus question: if this scenario is plausible, would that imply that Hawking radiation should cause a black hole to 'turn into' a neutron star at some point during the evaporation?