Date of Award

8-4-2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

Advisor(s)

Duncan Brown

Keywords

Core-collapse Supernova;Cosmic Explorer;Equation of State;Gravitational Waves;Neutron Stars;NICER

Abstract

Neutron stars are astrophysical laboratories to study extremely dense matter. The exact composition of the interior of a neutron star is yet unknown. However, recent observational and theoretical developments have provided crucial constraints on the properties of dense matter in neutron stars. In this thesis, we describe how we can use the astrophysical signals from neutron stars to measure their physical properties. We can use these measurements to determine the structure and composition of neutron star. We focus on two phases of the neutron star’s life and the astrophysical signals associated with it. First, we look at gravitational wave signals from core-collapse supernovae—the birthplace of neutron stars. We analyze the gravitational-wave signals obtained from three-dimensional simulations of core-collapse and calculate the detection prospects of these signals by the proposed next-generation detectors, such as Cosmic Explorer. We find that Cosmic Explorer can detect a supernova signal in the Milky Way galaxy. We analyze the first ∼ 10 ms of the gravitational-wave signal from core-collapse, where the signal is non-stochastic and primarily depends on the core rotation rate and its equation of state. We use data from numerical simulations of collapsing stars with rapidly rotating cores and develop a mapping between the physical parameters and the waveform morphology. We analyze the stochastic part of the signal, which is primarily generated due to the oscillations of the proto-neutron star. We develop a novel method to generate time-frequency spectrograms and we use them to measure the frequencies and energy associated with the quadrupolar f −mode oscillations of the proto-neutron star. Lastly, we determine the reproducibility of Riley et al. results, in which the authors analyze the X-ray data from NICER to measure the mass and radius of PSR J0030+0451 using X-ray pulse profile modeling. We find that using the data and software artifacts provided, we can not only reproduce their results but can extend them as well. Measuring the mass and radius of pulsar constrains its equation of state, and consequently its internal composition.

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Open Access

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