2021/08/19 by Peter Hammond, P. Hammond, Ian Hawke +1
Physics and Astronomy · #Astrophysics #Cosmology and Gravitation Theories #Equation of state #Gamma-ray bursts and supernovae #Neutron star #Nuclear matter #Nuclear physics #Physics #Pulsars and Gravitational Waves Research #Statistical physics #Thermal equilibrium #Thermodynamic equilibrium #Thermodynamics #Viscosity #Volume viscosity #Work (physics) #astro-ph.HE #gr-qc
paper · pdf · doi:10.1103/physrevd.104.103006
26 pages, 11 figures
arxiv created 2021/08/19 · openalex publication_date 2021/11/05 · arxiv updated 2021/11/09 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
In order to extract maximal information from neutron-star merger signals, both gravitational and electromagnetic, we need to ensure that our theoretical models/numerical simulations faithfully represent the extreme physics involved. This involves a range of issues, with the finite temperature effects regulating many of the relevant phenomena. As a step toward understanding these issues, we explore the conditions for \ensuremathβ-equilibrium in neutron star matter for the densities and temperatures reached in a binary neutron star merger. Using the results from our out-of-equilibrium merger simulation, we consider how different notions of equilibrium may affect the merger dynamics, raising issues that arise when attempting to account for these conditions in future simulations. These issues are both computational and conceptual. We show that the effects lead to, in our case, a softening of the equation of state in some density regions, and to composition changes that affect processes that rely on deviation from equilibrium, such as bulk viscosity, both in terms of the magnitude and the equilibration timescales inherent to the relevant set of reactions. We also demonstrate that it is difficult to determine exactly which equilibrium conditions are relevant in which regions of the matter due to the dependence on neutrino absorption, further complicating the calculation of the reactions that work to restore the matter to equilibrium.