Aspects of Binary Neutron Star Merger Remnants

Abstract

There are many properties that a binary neutron star merger remnant will have at birth which will dictate its evolution and fate. Currently, the best available methods for a proper understanding of binary neutron star merger remnants fall within numerical relativity. In this dissertation I cover original research which explores several important aspects of binary neutron star merger remnants. In particular, focus is given to the effects of morphology, composition, and magnetization on the evolution of binary neutron star merger remnants and their environments. Regarding the aspect of morphology, I present findings on the types of differentially rotating remnants that arise under realistic descriptions of the neutron star equation of state. I discuss the properties of differentially rotating neutron star solutions that can support masses over 2 times that of a non-rotating neutron star (termed ubermassive neutron stars). Additionally, I discuss the stability and dynamics of differentially rotating, quasi-toroidal neutron stars. Regarding the aspect of composition, I discuss results related to equations of state with high-density deconfinement phase-transitions that produce "hybrid stars": cousins of neutron stars with deconfined quark matter in their densest regions. I present findings on the maximum mass of uniformly and differentially rotating hybrid stars. Among other findings, I discuss the breakdown of universal relations in light of hybrid hadron-quark descriptions of dense matter. I also present results on the solution space of differentially rotating hybrid stars. Additionally, I discuss the stability of hybrid stars that are expected to be unstable and which have the same masses as neutron stars. I discuss unique gravitational wave signals that could point to the formation of hybrid stars. Finally, regarding the aspect of strong magnetization, I discuss the extensive code development required to update one of the only open-source general relativistic magnetohydrodynamics codes available, IllinoisGRMHD. Specifically, I discuss the implementation of realistic, finite temperature, tabulated equation of state capability within IllinoisGRMHD. Among other stringent test of the code, I demonstrate its ability to simulate strongly magnetized binary neutron stars with microphysical equations of state.