Constraining the Neutron Star Equation of State with Astrophysical Observables
Publisher
The University of Arizona.Rights
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction, presentation (such as public display or performance) of protected items is prohibited except with permission of the author.Abstract
Neutron stars provide a unique probe of the dense-matter equation of state (EOS), which in turn governs many astrophysical transients of interest today, including gamma-ray bursts, kilonovae, core-collapse supernovae, and gravitational waves from neutron star mergers. While many theoretical predictions for the dense-matter EOS have been calculated and constrained by laboratory experiments at low densities, these methods do not constrain the EOS at the densities or compositions reached in neutron star interiors. Recently, the EOS community has been driven by a push to incorporate new observations of neutron star phenomena. In this dissertation, I develop a multi-pronged framework for using astrophysical observations of neutron stars to constrain the dense-matter EOS. To that end, I develop a Bayesian statistical inference scheme to map from neutron star observables to an optimally parametrized EOS. I also derive several new methods to directly compare diverse types of observations, including a model-independent mapping between the moment of inertia of a pulsar and the neutron star radius, as well as a one-to-one mapping between the radius and the tidal deformability measured from a neutron star merger. These relationships allow us to directly compare radii inferred from gravitational wave data (or from a future moment of inertia measurement) to X-ray observations of the neutron star radius. With this mapping, I use the tidal deformability from the first neutron star merger, GW170817, to place new constraints on the neutron star radius of 10.2 < R < 11.7 km (68% confidence; for a flat prior in R), which are already competitive, though consistent with previous results from the X-ray community. Additionally, I develop a method for connecting gravitational wave data to the slope of the nuclear symmetry energy and I show that gravitational waves imply smaller values than have been found in Earth-based experiments. In the final chapters of my dissertation, I tie in dynamical phenomena to these constraints. Using results from state-of-the-art supernovae simulations, I show that such simulations are starting to accurately recreate the observed compact object mass distribution and I use these results to identify the origins of various features in the observed mass distribution. Finally, I introduce a new microphysical framework for extending models of the cold EOS to arbitrary temperatures and compositions, which can be used to simulate neutron star mergers or core-collapse supernovae with robust physics.Type
textElectronic Dissertation
Degree Name
Ph.D.Degree Level
doctoralDegree Program
Graduate CollegeAstronomy and Astrophysics