The atoms are crushed into their constituent subatomic particles, electrons and protons squeezed together to form neutrons, and what you have is basically neutron soup. This is what you find at the center of neutron stars - degenerate matter, held up by neutron degeneracy pressure, which we don't understand very well. Theoretically, you could squeeze further until the neutrons are torn apart into their constituent quarks. Most of the 'matter' inside a neutron isn't really matter at all, only a few percent in the form of quarks. The rest of the 'mass' of a neutron is actually energy, mediating the interactions between those quarks. So you could have a star that's been crushed beyond neutron degeneracy pressure, and is now quark soup instead of neutron soup. Quark soup being thousands of times denser. But we're still not at the level of a black hole.