Evidence for a hard equation of state in the cores of neutron stars

The equation of state for matter with energy density above 2 × 10 gm/cm is parametrized by P = kN , where N is the number density, Γ is the adiabatic index, and k a constant. Using this scheme to generate thousands of models, together with data on neutron star masses, it is found, for a core region with constant adiabatic index, that the central density must satisfy 10 gm/cm < ρc < 10 16 gm/cm, with Γ > 2.2. Further preliminary results indicate, based on the observed neutrino flux from supernova 1987a, that this number must be considerably higher, on the order of 3.5. These results provide evidence for a hard equation of state in the cores of neutron stars. Author’s note: This paper was originally submitted to the Astrophysical Journal circa 1995. It is uploaded here by request of new authors who are currently exploring the use of a similar parameterization scheme for similar purposes. The figures and tables referred to in the paper are no longer available.