Core-collapse supernova equations of state based on neutron star observations

Abstract: Many of the currently available equations of state for core-collapse supernova simulations give large neutron star radii and do not provide large enough neutron star masses, both of which are inconsistent with some recent neutron star observations. In addition, one of the critical uncertainties in the nucleon-nucleon interaction, the nuclear symmetry energy, is not fully explored by the currently available equations of state. In this article, we construct two new equations of state which match recent neutron star observations and provide more flexibility in studying the dependence on nuclear matter properties. The equations of state are also provided in tabular form, covering a wide range in density, temperature and asymmetry, suitable for astrophysical simulations. These new equations of state are implemented into our spherically symmetric core-collapse supernova model, which is based on general relativistic radiation hydrodynamics with three-flavor Boltzmann neutrino transport. The results are compared with commonly used equations of state in supernova simulations of 15 and 40 solar mass progenitors. We do not find any simple correlations between individual nuclear matter properties at saturation and the outcome of these simulations. However, the new equations of state lead to the most compact neutron stars among the relativistic mean-field models which we considered. The new models also obey the previously observed correlation between the time to black hole formation and the maximum mass of an s=4 neutron star.

• The paper introduces novel EOS models, SFHo and SFHx, that align supernova simulations with recent neutron star data.
• Simulations using 15 and 40 solar mass progenitors show that the new EOSs yield more compact neutron stars than traditional models.
• A correlation is established between black hole formation timing and the maximum mass of neutron stars, highlighting refined nuclear symmetry energy constraints.

Core-collapse Supernova Equations of State Derived from Neutron Star Observations

The study by A. W. Steiner, M. Hempel, and T. Fischer formulates and examines new equations of state (EOS) tailored for core-collapse supernova simulations. These EOSs are specifically designed to align with recent observations of neutron stars, addressing notable inconsistencies observed with traditional EOS models.

Neutron stars, formed in the aftermath of core-collapse supernovae, provide critical constraints for nuclear physics models. Traditional EOSs, often leading to neutron stars with large radii and insufficient maximum masses, appear inconsistent with recent astronomical measurements. Additionally, the nuclear symmetry energy, a critical parameter in nucleon-nucleon interactions, remains underexplored. Accordingly, this study introduces two novel EOSs, termed SFHo and SFHx, parameterized to improve the alignment with recent neutron star observational constraints and enhance flexibility in their application to nuclear matter properties.

These new EOS models are incorporated into spherically symmetric core-collapse supernova simulations utilizing a framework based on general relativistic radiation hydrodynamics and Boltzmann neutrino transport. Through simulations of progenitor stars with masses of 15 and 40 M$_\odot$, the EOSs are compared with traditional models.

The study establishes that new models such as SFHo and SFHx yield more compact neutron stars within the field of relativistic mean-field models evaluated. However, no simple correspondences were observed between individual nuclear matter properties at saturation density and the outcomes of these simulations. Additionally, a correlation was observed between the time to black hole formation and the maximum mass of a neutron star with entropy parameter $s=4$.

These findings have significant theoretical and practical implications. The proposed EOS models provide a more accurate encapsulation of nuclear physics constraints and recent neutron star observations. In practice, they offer an improved basis for supernova and neutron star simulations, essential for understanding these astrophysical phenomena. Nonetheless, bridging these findings with complex hydrodynamic simulations presents challenges, particularly given the intricate interplay between the nuclear EOS and simulation results. To address these challenges, further exploration of multi-dimensional and longer-term post-explosion simulations could reveal additional insights into the EOS impact on supernova dynamics and neutron star evolution.

In conclusion, the study advances the understanding of core-collapse supernova simulations by providing EOSs that better reflect neutron star observations. Future work may focus on refining these models and exploring their implications in multi-dimensional simulations to assess their broader astrophysical impacts.