Date of Award

June 2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

Advisor(s)

Duncan Brown

Keywords

accretion disks, binary black holes, binary neutron stars, common envelope physics, gravitational waves, nuclear equation of state

Subject Categories

Physical Sciences and Mathematics

Abstract

In recent years, the growing numbers of black hole and neutron star merger candidates observed by the Advanced LIGO (Laser Interferometer Gravitational-Wave Observatory) and Virgo gravitational-wave observatories are rapidly expanding the frontiers of astrophysics. The observations enable (i) direct measurements of properties of these compact objects with information extraction from the gravitational-wave data, and seek the understanding of (ii) mechanisms by which the close compact object binaries come into existence and (iii) the astrophysical processes that take place after they merge. This thesis presents work on all these three fronts (i) We present measurements of properties of the binary neutron star and black hole observations from the LIGO-Virgo observatories' second observing run, using Bayesian parameter estimation on the gravitational-wave data. During this observing run, LIGO-Virgo for the first time reported observations of gravitational waves from a binary neutron star inspiral, GW170817. This same source was also observed across the full electromagnetic spectrum. We combine gravitational-wave observations with a physical constraint on the component stars' equation of state and information from electromagnetic observations, to measure tidal deformabilities and radii of the neutron stars in the source binary. (ii) We explore the ``common envelope'' phase in the lives of binary stars in our universe. Common envelope is proposed to be the most probable mechanism of assembly of close compact object binaries. We present three-dimensional hydrodynamic simulations to model these episodes and discuss our understanding of the effect of this phase on the observable properties---such as masses and spins---of LIGO-Virgo's stellar mass black hole populations. (iii) We discuss the aftermath of compact object mergers where at least one of the components is a neutron star. We use three-dimensional General Relativistic Magnetohydrodynamic simulations to model one of the typical outcomes---black hole surrounded by matter in the form of an accretion disk---for a variety of merger scenarios. We present connections of the binary parameters to properties of the disks, and the nucleosythetic yields they produce. Using the simulation results, we predict properties of kilonova emissions from future neutron star mergers.

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