Type Ia supernovae (SNe Ia) are produced by the thermonuclear explosion of a white dwarf star. These supernovae (SNe) are the source of most iron in the universe. Additionally, the uniform peak brightness of SNe allows for precise distance calculations to remote points in the universe; these distance calculations lend themselves to more precise estimations of the scale of the universe. There have not been any recent observations of SNe Ia in our galaxy, but supernova remnants (SNRs) hold valuable information about the SNe themselves. There is, however, a gap in what we know about SNe and what we know through observing their remnants; the exact mechanism of the explosion is still not understood. By using data from a SN Ia model simulation 100 seconds after the explosion as the initial conditions for a hydrodynamic simulation, we can predict the appearance of the remnant hundreds of years later. Specifically, we aim to compare these results to the youngest known SNR (~100 years old) in our galaxy, G1.9+.03 Previous 2D simulations worked on the assumption of spherical symmetry; by starting with a 3D model we may find different result. With our model, we can predict the location of light elements expelled by the blast (carbon and oxygen) as well as moderate (sulfur and silicon) and heavy elements (iron) formed in the SN that produced the remnant. This may also give us some insight into the composition of the interstellar medium surrounding G1.9+.03

Gravitational accretion acts as a ubiquitous source of power for many celestial objects, yet how different conditions affect its fundamental properties remains poorly understood. Proposed in 1939, the Hoyle-Lyttleton model of accretion describes mathematically the behavior of a uniform gas cloud collecting onto a compact star. While this model has been found to predict generally accurate data, it is limited to steady, axisymmetric flow and fails to address many idiosyncrasies present in such a system. (Edgar, 2004) Recent studies of high-resolution simulations of HL accretion demonstrate instability in the mass accretion rate creating “breathing mode” oscillations of unclear origin. (Blondin & Raymer, 2012) We propose an in-depth investigation of accretion breathing modes using 2D simulations to characterize their nature as a function of changing conditions. By converting 3D simulations created by Blondin and Raymer (2012) into 2D, we will be able to study axisymmetric accretors of smaller radii in a high resolution grid for longer periods of time. We will examine the effects of changing the adiabatic index with a constant accretor radius and also observe results produced from an increasing mach number. Additionally, predictions made by Foglizzo (2001) will also be evaluated during this process in an attempt to find any inherent relationships between variables and explain the mechanism behind breathing mode oscillations.

Current simulations of core-collapse supernovae (CCSNe) suggest that the post-bounce shockwave stalls at a radius of approximately 50km. This stalled shockwave has been found to be unstable, in what is known as the Spherical Accretion Shock Instability (SASI). Revent numerical simulations suggest that the SASI plays an important role in reviving the explosion and powering CCSNe. Previous simulations involving SASI, however, are limited in their study of how rotation of the progenitor star affects the SASI. We propose tomore strongly consider progenitor star rotation in our simulations of CCSNe, more specifically using the VH-1 hydrodynamics code in two dimensions. Our goal with these simulations is to quantify the effects of rotation on the SASI,by measuring growth rates of the SASI, as well as other effects of rotation.

During core-collapse supernovae explosions large fluxes of neutrinos are emitted from the proto-neutron star formed at its center. As these neutrinos escape the flavor composition evolves: turbulence in the material flowing down upon the proto-neutron caused by the stalled shock wave and the super high neutrino density in core-collapse supernovae both have an effect. To date studies of the two effects have focused upon each separately even though both occur simultaneously. Using new codes for the neutrino evolution and hydro simulations we propose to calculate the neutrino evolution in the core of supernovae incorporating both turbulence and high neutrino density in an attempt to determine whether neutrino signatures of collective effects are modified by the turbulence and whether these changes can be observed. If they are detectable, then this will allow us to have a greater understanding of what is occurring during a future core-collapse supernova.

The mechanism behind Thermonuclear (Type Ia) Supernovae is believed to involve a white dwarf and a companion star, which could be a normal star (single-degenerate model) or a white dwarf (double-degenerate model). Finding the companion star would show that the companion star was not destroyed in the collision, implying a single-degenerate progenitor. Due to the sheer size of the supernovae and the number of candidate stars contained therein, it is necessary to determine the star's rough location before making an exhaustive search. It is thought that the companion star can be found at the explosion center, but assumptions that the explosion center would be at the remnant's geometric center have proved fruitless. However, these searches did not factor in the possibility that a nonuniform interstellar medium (ISM) density could cause an asymmetric expansion, which would cause the apparent geometric center to shift from the true explosion site. By running numerical hydrodynamics simulations modeling the effects of ISM density gradients, a collection of remnants can be formed, and a more reliable search location can be determined. The results will be applied by examining past searches on two young supernova remnants in order to determine if their search regions were insufficiently vast to account for such shifting.

The Spherical Accretion Shock Instability (SASI),in which a supernova shock wave stalls and produces a turbulent post-shock flow, has generally been accepted as an important phenomenon in core-collapse supernovae. However, the effects of the turbulence caused by SASI have yet to be thoroughly investigated; indeed, it has been hypothesized that two- and three-dimensional SASI simulations may produce incongruent results due to this turbulence. We therefore propose to use both two- and three-dimensional hydrodynamic simulations of core-collapse supernovae to study the growth of the SASI-driven turbulence. We will produce and analyze Fourier transform power spectra to quantify energy conversion (i.e. gravitational potential energy to the kinetic energy of turbulent flow) on different length scales. Finally, we hope to compare two- and three-dimensional resultsin particular, to determine if kinetic energy cascades toward small or large length scales, and if turbulence energy saturates at similar levels in two and three dimensions.

As some massive stars evolve, it is thought that long-duration (>2 sec) GRBs are produced from relativistic jets from the poles of the star before the star collapses forming a black hole. The length of time these jets produce these gamma-rays (T_engine) was always thought to be the same length of time that the bursts were detected (T₉₀). By creating GRB simulations at different redshifts, introducing noise and observing angle, the light curve and therefore detection of the burst changes. These simulations can show that bursts produced by the same stellar explosion could have different T₉₀ times, depending on the distance and observing angle.