Date of Award

August 2024

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Physics

First Advisor

Patrick Brady

Second Advisor

Jolien Creighton

Committee Members

Philip Chang, David Kaplan, Daniel Agterberg

Keywords

Binary Star, Black Hole, Common Envelope Evolution, Gravitational Wave, Hydrodynamics, Neutron Star

Abstract

Binary star systems are crucial for advancing our understanding of the universe. My doctoral research focuses on two related topics within the domain of binary star dynamics: gravitational waves from compact binary stars, and the evolution of the common envelope in stellar mass binaries.

In the era of multi-messenger astrophysics, swift identification and characterization of gravitational wave events is important for subsequent electromagnetic observations. The development of low-latency parameter estimation techniques is essential for providing astronomers with crucial information regarding the potential electromagnetic counterparts to gravitational wave signals. RapidPE is a highly parallelized parameter estimation scheme that achieves low-latency parameter estimation by limiting the intrinsic parameter space to a grid and utilizing Monte Carlo sampling in the extrinsic parameter space. My work introduces an improved intrinsic grid placement scheme called Adaptive Mesh Refinement (AMR) for RapidPE, enabling it to efficiently compute posterior distributions for intrinsic parameters by prioritizing computation in high-likelihood regions and overcoming biases from gravitational wave detection pipelines. With AMR, RapidPE can produce reliable source classification and posterior probability distribution for gravitational wave events within a minute with GPUs.

Common envelope evolution (CEE) is a phase in the evolution of a binary star system where two stars orbit inside a shared gaseous envelope and is crucial for the formation of many systems of astrophysical interest. Despite its importance, CEE is not well understood due to the complexity of the physics involved and the different timescales of its evolution. These complexities pose challenges for both simulation and observation of CEE. Once a system enters a Common Envelope phase, uncertainties persist regarding whether it ends in a merger and/or envelope ejection as well as the timescale and efficiency of the envelope ejection. To address these questions, I conduct a long timescale 3D simulation of a CEE using the moving-mesh hydrodynamic solver MANGA. This work shows that, if evolved long enough, complete envelope ejection can be achieved with solely the orbital energy alone without the need for reheating from recombination or jets. Additionally, the envelope enters a phase of homologous expansion in our simulation. This homologous expansion of the envelope would likely simplify calculations of the observational implications such as light curves.

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