Date of Award
Doctor of Philosophy
William R. Hix
Otis Earl Messer II, Michael W. Guidry, Jack Dongarra, Thomas Papenbrock
Observations of nuclear abundances in core-collapse supernova (CCSN) ejecta, highlighted by γ-ray [gamma-ray] observations of the 44Ti [titanium-44] spatial distribution in the nearby supernova remnants Cassiopeia A and SN 1987A, allow nucleosynthesis calculations to place powerful constraints on conditions deep in the interiors of supernovae and their progenitor stars. This ability to probe where direct observations cannot makes such calculations an invaluable tool for understanding the CCSN mechanism. Unfortunately, despite knowing for two decades that supernovae are intrinsically multi-dimensional events, discussions of CCSN nucleosynthesis have been predominantly based on spherically symmetric (1D) models, which employ a contrived energy source to launch an explosion and often ignore important neutrino effects. As part of the effort to bridge the gap between first-principles simulations of the explosion mechanism and observations of both supernovae and supernova remnants, this dissertation investigates CCSN nucleosynthesis with self-consistent, axisymmetric (2D) simulations using the multi-dimensional radiation-hydrodynamics code Chimera. These models represent a necessary improvement over their parameterized counterparts in characterizing the impact of the hydrodynamically unstable, neutrino-driven supernova explosion on the ejecta composition and distribution.
Computational costs have traditionally constrained the evolution of the nuclear composition within multi-dimensional CCSN models to, at best, a 14-species α-network [alpha-network] capable of tracking only (α,γ) [(alpha,gamma)] reactions from 4He [helium-4] to 60Zn [zinc-60]. Lagrangian tracer particles are commonly used to extend the nuclear network evolution by incorporating more realistic networks in post-processing calculations. This work presents a novel analysis of these nucleosynthesis calculations, including the impact of uncertainties therein, for four ab initio axisymmetric CCSN models initiated from stellar metallicity, non-rotating progenitors of 12, 15, 20, and 25 solar masses and evolved with the smaller α-network to more than a second after the launch of an explosion. The results of this analysis address many lingering concerns from parameterized 1D nucleosynthesis models. Facilitated by recent improvements to the physical approximations and computational performance of Chimera, future and ongoing simulations are beginning to address the implications of this analysis, highlighted by the need for larger in situ reaction networks and more developed explosion morphologies.
Harris, James Austin, "Nucleosynthesis in Self-Consistent Core-Collapse Supernova Models using Multidimensional Chimera Simulations. " PhD diss., University of Tennessee, 2015.