THE INNER BOUNDARY OF A NEUTRON-STAR CRUST

The phase boundary between the liquid matter of the interior of a neut ron star and the solid matter that comprises the crust is studied. The matter is assumed to consist of electrons and non-relativistic neutro ns and protons in beta equilibrium. The characteristic used to identif y the phase boundary is the onset of instability of the uniform matter against proton clustering, and it is examined for four interactions e ither used previously in astrophysical studies - Skyrme 1', SkM and FP S - or proposed here as an improvement - FPS21. The relationship of th is important property of neutron-star matter to the neutron-matter cha racter of each interaction is explored. Characteristic densities assoc iated with proton drip and with the liquid-gas boundary of one- and tw o-fluid models of the matter are compared with the instability density . Properties of some other effective interactions, relativistic and no n-relativistic, are compared with those of the interactions discussed. The desirability of more calculations of neutron-matter properties, a nd of the utilization of those that do exist when formulating dense-ma tter equations of state, is emphasized. For the improved interaction F PS21, the crust fraction of the moment of inertia of a neutron star is estimated.