Due to ever improving hydrodynamic simulations, our understanding of how massive stars explode has allowed us to make increasingly confident predictions of the neutrino burst signal from the next supernova in our Galaxy. With this signal, we hope to answer the many outstanding questions about the core dynamics of a supernova and the shockwave that propagates through the star. But first, we must be able to decode these signals, which requires understanding the flavor oscillation that occurs as the neutrinos propagate through the star and towards Earth. We propose a computational analysis that uses the density and neutrino information of a particular hydrodynamical supernova model to predict the neutrino signals that would be detected. Our calculations will take into account flavor oscillations that occur due to collective flavor effects and the evolution of the Mikheyev, Smirnov & Wolfstein (MSW) conversion, and we will test both normal and inverted neutrino mass hierarchies. Our goal is to test whether shockwaves in supernovae can be observed in current and next generation neutrino detectors and what information we may be able to extract.

It is known that planetesimals and asteroids are created by the accumulation of inter- stellar dust, however the exact process is not understood. With the difference in sizes spanning at least 12 orders of magnitude, there is knowledge to be gained in how these N-bodies collide, agglomerate, and fragment. Prior research in the topic has established regimes for the results of collisions at various velocities, but neglects gravity. In addition, experiments reveal that granular materials form force chains, resulting in non-uniform forces throughout the body. We propose new simulations that take into account grav- ity, dissipation of energy, and use a potential function for overlapping particles to both proxy deformation and to create force chains. These new simulations will help model the growth of N-body solids through collisions of smaller bodies, and reveal more in- formation about the distribution of energy in the remnants of collisions and threshold velocities that result in destruction of the object.

Supergiant Fast X-Ray Transients (SFXTs) are a subclass of High-Mass X-Ray Binaries (HMXBs) that consist of a neutron star and OB supergiant donor star. These systems display short, bright x-ray flares lasting for a few minutes to a few hours with luminosities reaching 10³⁶ erg/s, several orders of magnitude larger than the quiescent luminosities of 10³² erg/s. While the exact mechanism producing these flares is unknown, three models have been proposed: accretion from anisotropic winds such as those ejected from rapidly rotating Be stars, the accretion of clumps created by stellar wind instabilities, and the interplay between magnetic and centrifugal gating mechanisms that alternately inhibit and enable accretion. Thus far, analytic models have relied on the predictions of Hoyle-Lyttleton accretion, which ignore many idiosyncrasies in the system and limit the models to steady, axisymmetric flow. We propose to test the clumpy wind hypothesis by using the VH-1 hydrodynamics code which will model the complex time-varying nature of flow in 3D. We will model clump accretion over parameters such as clump mass, clump radius, and distance from accretion axis and use the mass accretion rate to track the x-ray luminosity of the system. The x-ray light curves produced by our simulations will be compared to observational curves in order to locate consistent behavior between the two.

High-resolution radio and X-ray images of several young Type Ia supernova remnants (SNRs) such as SN 1006 and Tycho show unexpected protrusions or knots beyond the mean shock radius. The mechanism for formation of these knots has been debated in recent years, yielding two major theories; hydrodynamic instabilities, and clumps of higher density ejecta formed in the early stages of the SN explosion. Clumps formed very early would carry clues to the process by which Type Ia supernovae explode, but might also account for a discrepancy between theoretical and observed distances between the forward shock (FS) and contact discontinuity (CD) in young SNRs, which has been used to argue for efficient shock acceleration. Recent studies have produced varying results, largely due to the variety of techniques used and parameters taken into consideration during simulation. We intend to perform hydrodynamic simulations of the evolution of a remnant from an age of a few years to hundreds of years, using the VH-1 hydrocode in one, two, and three dimensions. By running lower resolution, lower dimensionality simulations over a large range of initial conditions, we will identify the most significant parameters to study with higher resolution 3D simulation. By determining the mechanism that causes the development of knots on young SNRs, insight will be gained on the early states of supernovae and observed distances between the FS and CD may be justified.

The Galaxy's youngest known supernova remnant (SNR) is G1.9+0.3, which is likely left from a Type Ia supernova (SN) after the explosion of a white dwarf. While previous symmetric models of Type Ia explosions tend to be highly stratified with the heavier elements in the center and the lighter elements in the outer shells, observations of G1.9+0.3 show otherwise. The gap between simulations and observations shows that asymmetric models are needed to improve our understanding of the explosion mechanism in the dying star. We will use as input different models of Type Ia explosions at an age of 100 seconds provided by other researchers to study asymmetry and the different assumptions about the location and properties of the ignition which affect the location of elements in the SNR. This will include using 3D simulations and comparing those to 2D and 1D simulations. We propose to use the VH-1 hydrodynamics code with these models to evolve a Type Ia SN to a few hundred years in age to reproduce the observations of G1.9+0.3. With these models, we can predict the amount and location of stellar elements expelled in the Type Ia SN explosion implied by these models. This will further our understanding of how these supernovae explode and the effects that this asymmetry has on nucleosynthesis.

Gamma ray bursts are brief flashes of gamma ray photons that are detectable from Earth-orbiting satellites, originating in either massive collapsing stars or from the collision of neutron stars and/or black holes. Many previous studies cite the collapsar model as the origin of gamma ray bursts. Yet, previous studies have not determined the structure of the cocoon, nor how its material affects the creation of the gamma ray burst. The purpose of this study is to not only determine the composition of the cocoon structure in gamma ray burst progenitors, but also to compare the cocoon emissions from different star types. Using data from tracer-particle simulations, I will analyze the observational signature of cocoons from different progenitor stars with different metallicity, radius, and mass.

Long-duration gamma-ray bursts produced by the cores of massive stars nearing the end of their evolution are characterized by their energy-rich jets and surrounding high-pressure cocoons. Though the literature reveals insight into the general formation and photospheric emissions of these cocoons, their composition has not yet been modeled. Generally, it is assumed that the cocoon divides into an inner and outer part, a jet matter and stellar matter division, and that the two either mix fully or not at all. We propose to investigate this by modeling the mixing of the cocoon. We will do so by adding tracer particles to special relativistic hydrodynamic simulations of collapsars to follow the mixing of the jet and stellar material, thus studying the cocoon composition. These simulations will later be used to predict the cocoons’ corresponding radiation and determine specific observational signatures to enable us to put constraints on the progenitor star’s structure that produces such jets.

The abundances of elements heavier than helium result from stellar nucleosynthesis. Core-collapse supernovae play an important role in the formation of iron-group elements and other massive isotopes. Neutrinos, which can undergo flavor transformations, play an important role in the star during the core-collapse and explosion. There are only a few successful simulations of core-collapse supernovae explosions with 8 to 10 Msun stars in spherical symmetry, yet we still do not fully understand the mechanisms that drive the explosions of supernovae. These simulations do not take into account the effects of collective neutrino flavor oscillation. In this project we will investigate the effects of collective flavor oscillations on the nucleosynthesis. We will use the core-collapse supernova simulation for an 8.8Msun star by Huedepohl et al together with neutrino flavor oscillations and calculate the nucleosynthesis using a nuclear reaction network. We will then compare the results that take into account the neutrino flavor oscillations to the results that ignore them. This project will allow us to understand the nucleosynthesis yields for the explosion of a core-collapse supernova as well as understand the potential effects of multi-flavor neutrino oscillations has on stellar nucleosynthesis.