Institute for Advanced Study Astrophysics Seminar

Binary neutron star mergers provide a unique probe of the neutron star equation of state (EOS) across a wide range of parameter space, from the zero-temperature EOS during the inspiral to the finite-temperature EOS following the merger. In this talk, I will start with an overview of what we have learned about the cold EOS from the first binary neutron star mergers, focusing in particular on the tidal deformability constraints from event GW170817, what these constraints imply for the neutron star radius, and how such constraints compare to previous X-ray measurements. In the second part of my talk, I will discuss what additional EOS information can be extracted by studying the late-stages of a binary neutron star merger, during which time the matter is heated to significant temperatures. I will present a new set of binary neutron star merger simulations, which use a parametrized framework for calculating the finite-temperature EOS. This new EOS framework is based on a two-parameter approximation of the particle effective mass and includes the leading-order effects of degeneracy in the finite-temperature part of the EOS, providing a significant improvement over the ideal-fluid based approximations that are commonly used in simulations today. I will show that including the effects of degeneracy can significantly affect the post-merger gravitational wave signal and the amount of ejected merger, compared to the canonical approach.