Solid cores in neutron stars?

Abstract

The possibility of a liquid-to-solid phase transition in neutron stars is investigated. The ground-state energy of neutron matter is calculated by means of Pandharipande's variational LOCV method, and the ground-state energy of a neutron solid is calculated by a similar method. Both bcc and fcc structures and two possible spin configurations (parallel spins and “mixed” spins) are considered. The possibility of a phase transition from normal neutron matter into a neutron solid is then considered, but no phase transition is found to occur for the specific two-body potential assumed and the chosen spin configuration. The liquid is in general energetically favourable to the solid, and we get very poor localization of the neutrons in the lattice at energy minimum for the solid. The bcc structure, however, is found to be energetically favourable to the fcc structure.