Other Astrophysics and Astronomy Commons^™

Sub-Chandrasekhar Type Ia Supernovae Scenarios With Increased Pathways For Neutronization, Fernando Hernan Rivas

Doctoral Dissertations

Type Ia supernovae are thermonuclear explosions of white dwarfs (WD), electron-degenerate cores of old intermediate mass stars(under 8$M_{\odot}$). Reaching energies of $10^{51}$\si{\erg}, they outshine whole galaxies as they synthesize and distribute most of the iron group elements (IGE; V, Cr, Mn, Fe, Co, Ni) into the interstellar medium, thus being one of the main agents in cosmic chemical evolution. Also, given their notably homogeneous lightcurves, they form the last step in the cosmic distance ladder outdistancing Cepheid variables by orders of magnitude. Though calibration of said lightcurves is dependent on a high number of confirmed events, the limits of statistical …

Analysis Of A Controlled Approximation For Explicit Integrations Of Stiff Thermonuclear Networks, Nicholas Brey

Masters Theses

The current standard method to solve stiff coupled differential equations relies on implicit integration methods. Explicit methods are generally avoided due to the extremely small and limiting timesteps they allow when the equations are stiff. However, implicit methods are computationally expensive because of the complex calculations that need to be done at each time step. An explicit integration method can do these calculations quicker and, if allowed to take comparable timesteps to the implicit ones, would allow the entire calculation to be done faster. Previous work by Dr. Guidry, Dr. Endeve, Dr. Hix and Dr. Billings has shown that, in …

Core-Collapse Supernova Simulations With Spectral Two-Moment Neutrino Transport, Ran Chu

Doctoral Dissertations

The primary focus of this dissertation is to develop a next-generation, state-of-the-art neutrino kinetics capability that will be used in the context of the next-generation, state-of-the-art core-collapse supernova (CCSN) simulation frameworks \thornado\ and \FLASH.\index{CCSN} \thornado\ is a \textbf{t}oolkit for \textbf{h}igh-\textbf{or}der \textbf{n}eutrino-r\textbf{ad}iation hydr\textbf{o}dynamics, which is a collection of modules that can be incorporated into a simulation code/framework, such as \FLASH, together with a nuclear equation of state (EOS)\index{EOS} library, such as the \WeakLib\ EOS tables. The first part of this work extends the \WeakLib\ code to compute neutrino interaction rates from~\cite{Bruenn_1985} and produce corresponding opacity tables.\index{Bruenn 1985} The processes of emission, …

Extending Core-Collapse Supernova Simulations: From The Onset Of Explosion To Shock Breakout, Michael A. Sandoval

Doctoral Dissertations

A core-collapse supernova (CCSN) is the result of a massive star’s core collapsing due to the inability of electron degeneracy pressure to provide sufficient support against gravity. Currently, there is a disconnect between when most three-dimensional CCSN simulations end (seconds) and when the explosion would reach the surface of the star and become visible (hours to days). We present three-dimensional simulations of CCSNe using the FLASH code that follow the progression of the explosion to the stellar surface, starting from neutrino-radiation hydrodynamic simulations of the first seconds performed with the Chimera code. We consider a 9.6-M_⊙ zero-metallicity progenitor, starting …

Accuracy And Stability Of Integration Methods For Neutrino Transport In Core Collapse Supernovae, Kyle A. Gregory

Chancellor’s Honors Program Projects

No abstract provided.

Surface Plasmon Modes In Toroidal Nanostructures And Applications, Marouane Salhi

Doctoral Dissertations

A special interest in Plasmon mode resonance in toroidal nano-particles where a full and comprehensive analytical investigation is presented for different toroidal nano-structure within the quasi-static approximation. Then the optical response of gold nanorings and the associated near-field mapping when exposed to a broadband electromagnetic wave were obtained by the implementation of numerical methods to solve for the transient response. The numerical and analytical investigation lead to the design of an optical nano-trapping system and the identification of strong coupling interaction between toroidal plasmons and J-aggregate dye molecules a promising component in the design of novel optoelectronic material.

Neutrino Signatures In Terrestrial Detectors From Two- And Three-Dimensional Core-Collapse Supernovae Simulations, Tanner Brooks Devotie

Masters Theses

Core-collapse supernovae (CCSNe) are driven by neutrino emission and are the most prodigious sources of neutrinos in the Universe. Importantly, the neutrino radiation from CCSNe is emitted from deep in the explosion and can provide information about physical processes taking place in the newly-born neutron star at the heart of the event. We examine the four-flavor (i.e. ν_e, ν_e, ν_x and ν_x) [electron, muon and tau neutrinos along with their anti-matter counterparts] signature of CCSNe neutrino emission in various neutrino detector types. We use data from the multidimensional Chimera (Lentz et al., 2015) …

On The Spin Evolution Of Isolated Pulsars, Oliver Quinn Hamil

Doctoral Dissertations

Neutron stars are the remnants of supernova explosions, and harbor the densest matter found in the universe. Because of their extreme physical characteristics, neutron stars make superb laboratories from which to study the nature of matter under conditions of extreme density that are not reproducible on Earth. The understanding of QCD matter is of fundamental importance to modern physics, and neutron stars provide a means of probing into the cold, dense region of the QCD phase diagram.

Isolated pulsars are rotating neutron stars that emit beams of electromagnetic radiation into space which appear like lighthouses to observers on Earth. Observations …

The Effects Of Realistic Nuclear Kinetics, Dimensionality, And Resolution On Detonations In Low-Density Type Ia Supernovae Environments, Thomas L. Papatheodore

Doctoral Dissertations

Type Ia supernovae are most likely thermonuclear explosions of carbon/oxygen white dwarves in binary stellar systems. These events contribute to the chemical and dynamical evolution of their host galaxies and are essential to our understanding of the evolution of our universe through their use as cosmological distance indicators. Nearly all of the currently favored explosion scenarios for these supernovae involve detonations. However, modeling astrophysical detonations can be complicated by numerical effects related to grid resolution. In addition, the fidelity of the reaction network chosen to evolve the nuclear burning can alter the time and length scales over which the burning …

Three Dimensional Equation Of State For Core-Collapse Supernova Matter, Helena Sofia De Castro Felga Ramos Pais

Doctoral Dissertations

The core-collapse supernova (CCSN) phenomenon, one of the most explosive events in the Universe, presents a challenge to theoretical astrophysics. Stellar matter in supernovae, experiencing most extreme pressure and temperature, undergoes transformations that cannot be simulated in terrestrial laboratories. Construction of astrophysical models is the only way towards comprehension of CCSN. The key microscopic input into CCSN models is the Equation of State (EoS), connecting the pressure of stellar matter to the energy density and temperature, dependent upon its composition. Of the large variety of forms of CCSN matter, we focus on the transitional region between homogeneous and inhomogeneous phases. …

A Search For Volatile Ices On The Surfaces Of Cold Classical Kuiper Belt Objects, Daine Michael Wright

Masters Theses

The surprisingly complex dynamical distribution of small bodies among and beyond the orbits of the planets has changed our understanding of Solar System evolution and planetary migration. Compositional information about the small bodies in the Solar System provides constraints for models of Solar System formation. According to most models, the Kuiper Belt population known as the cold classicals formed at distances far enough from the Sun for these objects to be composed of an appreciable fraction of volatile ices of diverse composition (H₂O, CO₂, CH₄, light hydrocarbons, e.g. CH₃OH) and their orbits …

Advancements In Modeling Self-Consistent Core-Collapse Supernovae With Chimera, Merek Austin Chertkow

Doctoral Dissertations

Using a sophisticated program named CHIMERA, we perform numerical simulations of the end of a massive star's life when its core can no longer support itself through electron degeneracy pressure. After a violent collapse to super-nuclear densities, the core releases its binding energy (10^53 ergs) in the form of neutrinos. Simulations have shown that a small fraction of these neutrinos' energy is deposited into the matter above the forming neutron star, which drives a delayed explosion. Throughout this process, the oxygen and lighter elements that had composed the star's outer-core and envelope experience shock-driven explosive nucleosynthesis, forming newly synthesized heavy …

Evaluating Explicit Methods For Solving Astrophysical Nuclear Reaction Networks, Elisha Don Feger

Doctoral Dissertations

Many systems of physical interest are difficult to manage computationally because of the intrinsic nature of the equations that govern them. Many of these systems of equations are stiff, meaning that the standard approach to solving them is with implicit methods, because explicit methods either are unstable or require timesteps too small to be computationally efficient. Presented here is a study of explicit methods that decouple stability from accuracy under certain conditions, allowing for larger timesteps to be taken.