A Second Relativistic Mean Field and Virial Equation of State for Astrophysical Simulations

TL;DR

This paper develops a new relativistic mean field and virial equation of state for nuclear matter, covering wide temperature, density, and proton fraction ranges, to improve astrophysical simulations of supernovae and neutron stars.

Contribution

It introduces a second EOS based on the FSUGold interaction, extending previous work with NL3, and provides detailed tables for astrophysical modeling.

Findings

FSU1.7 EOS supports neutron stars up to 1.7 solar masses.

Modified FSU2.1 EOS supports neutron stars up to 2.1 solar masses.

Differences in thermodynamic properties compared to previous EOSs are analyzed.

Abstract

We generate a second equation of state (EOS) of nuclear matter for a wide range of temperatures, densities, and proton fractions for use in supernovae, neutron star mergers, and black hole formation simulations. We employ full relativistic mean field (RMF) calculations for matter at intermediate density and high density, and the Virial expansion of a non-ideal gas for matter at low density. For this EOS we use the RMF effective interaction FSUGold, whereas our earlier EOS was based on the RMF effective interaction NL3. The FSUGold interaction has a lower pressure at high densities compared to the NL3 interaction. We calculate the resulting EOS at over 100,000 grid points in the temperature range $T$ = 0 to 80 MeV, the density range $n_B$ = 10$^{-8}$ to 1.6 fm$^{-3}$, and the proton fraction range $Y_p$ = 0 to 0.56. We then interpolate these data points using a suitable scheme to generate a thermodynamically consistent equation of state table on a finer grid. We discuss differences between this EOS, our NL3 based EOS, and previous EOSs by Lattimer-Swesty and H. Shen et al for the thermodynamic properties, composition, and neutron star structure. The original FSUGold interaction produces an EOS, that we call FSU1.7, that has a maximum neutron star mass of 1.7 solar masses. A modification in the high density EOS is introduced to increase the maximum neutron star mass to 2.1 solar masses and results in a slightly different EOS that we call FSU2.1. The EOS tables for FSU1.7 and FSU2.1 are available for download.