EoS for hot neutron stars

Abstract

We review the equation of state (EoS) models covering a large range of temperatures, baryon number densities and electron fractions presently available on the COM-POSE database. These models are intended to be directly usable within numerical simulations of core-collapse supernovae, binary neutron star mergers and proto-neutron star evolution. We discuss their compliance with existing constraints from astrophysical observations and nuclear data. For a selection of purely nucleonic models in reasonable agreement with the above constraints, after discussing the properties of cold matter, we review thermal properties for thermodynamic conditions relevant for core-collapse supernovae and binary neutron star mergers. We find that the latter are strongly influenced by the density dependence of the nucleon effective mass. The selected bunch of models is used to investigate the EoS dependence of hot star properties, where entropy per baryon and electron fraction profiles are inspired from proto-neutron star evolution. The Γ -law analytical thermal EoS used in many simulations is found not to describe well these thermal properties of the EoS. However, it may offer a fair description of the structure of hot stars whenever thermal effects on the baryonic part are small, as shown here for proto-neutron stars starting from several seconds after bounce.

Hot neutron stars and their equation of state

“…Finally in APR the effective Landau mass decreases with density. The same is true for Skyrme-like interactions, although the density dependence is different [64].…”

“…The BHF and FSU2H EOSs have been complemented at low densities in a thermodynamic consistent way with the LS220 and HS(IUF) [25] EOSs, respectively. Clusterisation in the outer layers partially washes out the dependence on effective interactions and introduces in exchange some dependence on cluster modelling [64].…”

“…At this point it is important to stress that, for given particle degrees of freedom and fixed values of density and entropy per baryon, the temperature is correlated with the values of Landau (for non-relativistic models) or Dirac (for relativistic models) effective masses [64] and isospin asymmetry of the matter [39,65,66]. Therefore the low (high) temperature values produced by the BHF (variational) EOS models can be explained by the moderate (extreme) isospin asymmetries that characterize these classes of models (see the bottom panel of Fig.…”