| MadSci Network: Astronomy |
Neutrons (and protons) are made up of smaller particles called "quarks." Quarks have never been seen alone in the lab, because the forces between them are so strong. It takes so much energy to pull two quarks apart that you add enough energy to the system to create a quark and an anti-quark (good ol' E=mc2) which quickly join up with the original quarks and form two new compound particles.
Three quarks join together to form a neutron or proton. Presumably, when the neutron degeneracy is overcome, the resulting compression overcomes the barriers distinguishing one neutron from the next, and a massive collection of quarks results---very briefly. As far as we know, quarks could be perfect mathematical points---no dimension at all, so it's hard to imagine what goes on next. You've moved into the realm where the Standard Model of quantum mechanics meets General Relativity, and scientists haven't figured out how to completely merge these two theories yet. Part of the problem is that we don't have many systems like black holes and neutron stars where both quantum mechanics and gravity are relevent. Then again, not having any of those violent systems close enough to study might not really be a problem.
To learn more about fundamental particles, I highly recommend the Particle Adventure. A very nice exploration of fundamental particles, including quarks and the Pauli exclusion principle that gives rise to electron and neutron degeneracy. They don't directly tie in to the astrophysical systems, but having studied from the astronomy side it should be useful to you.
Hope this helped.
Jay
Try the links in the MadSci Library for more information on Astronomy.