Neutron star matter at high temperatures and densities. I - Bulk properties of nuclear matter

Abstract

Calculations of the thermodynamic properties of uniform dense matter at finite temperature are performed using the Skyrme (1956) nuclear interaction. The calculations are valid for arbitary proton concentrations and temperatures. The equation of state is compared with earlier investigations done for a few restricted cases. In order to understand the conditions under which one might expect to find nuclei immersed in a sea of nucleons, the coexistence of two fluid phases with different proton concentrations is investigated. At zero temperature, nuclei with proton fractions in the range 0.044-0.335 may coexist with a pure neutron fluid, but at lower proton fractions protons 'drip' as well. At finite temperatures, nuclear droplets with proton fractions up to 0.5 may coexist with fluid also containing up to 50% protons. A phase diagram for nuclear matter is presented. The critical temperature, as a function of proton concentration, above which no coexistence is possible and nuclei evaporate, is established. Its maximum value is 20 MeV, which occurs in the case of symmetric nuclear matter.