Crystallization and Torsional Oscillations of Superdense Stars

Abstract

The nuclei of a piece of iron compressed to a density of 108 g cm3~ will arrange themselves into a body centred cubic lattice with a melting temperature near 2 × 108 °K, corresponding to a thermal energy about 1 per cent of the coulomb repulsion between neighbouring nuclei1. For matter near the end point of thermonuclear evolution compressed to still higher densities the dominant nuclear species shift towards very neutron rich nuclei, with Z between 30 and 50, which arrange themselves into crystal lattices with an even greater melting temperature. Crystallization among nuclei can occur up to densities close to that of conventional nuclear matter where those protons that remain cluster into very neutron-rich nuclei which are surrounded by and exchange neutrons with an ambient degenerate neutron sea. Because canonical neutron star interiors are estimated to cool to an average temperature below 5 × 108 °K in less than 103 years2–4, the outer regions of such stars should be solid.