Quarks in a Crowd: The Recipe for a Solid Core
Inside a neutron star, matter is squeezed so hard that atomic nuclei stop being separate clumps. Neutrons and protons get closer together, and their innards, quarks, begin to feel their neighbors through the walls of their 'bags'.
A neutron star is a sphere about the size of a small city but with a mass of one and a half Suns.