title: Equation of state of hot and dense matter in astrophysics and in the laboratory
Creators: name: Huth, Sabrina
Publisher: name: UNSPECIFIED
Year: 2023

description: For the interpretation of high-energy astrophysical phenomena such as supernova explosions or neutron star collisions, a thorough understanding of matter at supranuclear densities is necessary. Unfortunately, our current knowledge of dense matter as present in neutron star cores is limited. Novel constraints on the equation of state of neutron star matter are provided by gravitational wave observations of neutron star mergers such as GW170817 and measurements of neutron star radii by NASA's NICER mission. Recently, microscopic calculations of pure neutron matter are used as a basis for the construction of new equation of state parametrizations. However, extrapolations to high densities are required here as these calculations are only available up to about nuclear saturation density. Core-collapse supernovae and neutron star mergers probe an even broader range of temperature and electron fraction in comparison to cold isolated neutron stars. For astrophysical applications, commonly used equations of state are mostly not consistent with microscopic calculations and recent astrophysical observations. The construction of novel equation of state parametrizations that are in agreement with the latest constraints from nuclear physics and observations will facilitate significant advances in nuclear astrophysics. In this thesis, we provide new equations of state for core-collapse supernova and neutron star merger simulations. To this end, we introduce a parametrization for the nucleon effective mass that reflects novel microscopic calculations up to twice saturation density. The effective mass is essential to accurately describe thermal effects, which govern the proto-neutron star contraction in core-collapse supernovae. To constrain the parameter range of the equation of state we use results from chiral effective field theory calculations at nuclear densities and functional renormalization group computations at high densities that are based on quantum chromodynamics. In addition, constraints from mass measurements of heavy neutron stars, the gravitational wave signal of GW170817, and the first NICER results are implemented as well. We investigate the results for the predicted ranges for the equation of state and neutron star properties such as the neutron star radius and maximum mass. From this equation of state functional, we choose a set of representative equations of state to systematically study the impact of the nucleon effective mass and nuclear matter properties in core-collapse supernova simulations. For this, equation of state tables can be computed using the liquid-drop model with a single nucleus approximation that cover a wide range of densities, temperatures, and electron fractions as required by astrophysical simulations. Moreover, we combine information from astrophysical multi-messenger observations of neutron stars and from heavy-ion collisions of gold nuclei at relativistic energies with microscopic nuclear theory calculations via Bayesian inference to refine our knowledge of dense matter. Heavy-ion collision experiments offer complementary information at intermediate densities where theoretical calculations as well as observations are less sensitive to. Our results show an increase in the pressure in dense matter compared to previous studies when data from heavy-ion collisions is included. This leads to a shift in neutron-star radii towards larger values, similar to recent observations by the NICER mission. We conclude that constraints from heavy-ion collision experiments and multi-messenger observations are strikingly consistent with each other. This work highlights how joint analyses can shed light on the properties of neutron-rich nuclear matter over the density range probed in neutron stars.