Nuclear matter
![Phases of nuclear matter with equal numbers of neutrons and protons; Compare with Siemens & Jensen.[1]](/Images/godic/202501/30/Phases_of_Nuclear_Matter0107.JPG")
![Cross-section of neutron star. Densities are in terms of ρ0 the saturation nuclear matter density, where nucleons begin to touch. Patterned after Haensel et al.,[7] page 12](/Images/godic/202501/30/Neutron_star_structure0107.JPG")
Nuclear matter is an idealized system of interacting nucleons (protons and neutrons) that exists in several phases that as yet are not fully established. It is not matter in a nucleus, but a hypothetical substance consisting of a huge number of protons and neutrons interacting by only nuclear forces and no Coulomb forces. Volume and the number of particles are infinite, but the ratio is finite. Infinite volume implies no surface effects and translational invariance (only differences in position matter, not absolute positions).