COSMIC LABORATORY. “The nature of the matter in the cores of neutron stars is of great interest to nuclear physicists and astrophysicists alike, but its properties are difficult to establish in terrestrial laboratories. This is because neutron star cores reach a few times the density of matter in terrestrial nuclei and yet they are strongly degenerate and they have far more neutrons than protons. The core matter thus occupies a different phase than is accessible in laboratories.”
https://link.springer.com/chapter/10.1007/978-3-662-62110-3_1