New ab initio constrained extended Skyrme equations of state for simulations of neutron stars, supernovae, and binary mergers

II. Thermal response in the suprasaturation density domain

National Institute for Physics and Nuclear Engineering (IFIN-HH) RO-077125 Bucharest, Romania

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Received: 26 September 2025
Accepted: 3 November 2025

Abstract

Context. Numerical simulations of core-collapse supernovae, mergers of binary neutron stars, and the formation of stellar black holes, using standard Skyrme interactions, have established clear correlations between the evolution of these processes, the characteristics of hot compact objects, as well as neutrino and gravitational wave signals, and the value of effective nucleon mass at the saturation density. However, the density dependence of the effective nucleon mass in these models does not align with the predictions of ab initio models with three-body forces.

Aims. We investigated the thermal response for a set of extended Skyrme interactions that feature widely different density dependencies of the effective mass of nucleons.

Methods. We studied thermal contributions to the energy density and pressure, along with several thermal coefficients, over wide domains of density, temperature, and isospin asymmetry that are relevant for the physics of hot compact objects.

Results. For some of the effective interactions, the thermal pressure is negative at high densities. This results in hot compact stars supporting less mass before collapsing into a black hole compared to their cold counterparts. Moreover, the higher the temperature, the lower the maximum mass that the hot star can support.