Investigating astrophysical r-process sites: code (r-Java 2.0) and model (dual-shock quark nova) development
Creators: name: Kostka, Mathew
Publisher: name: Graduate Studies
Year: 2014
Subjects: Astronomy and Astrophysics
Physics--Nuclear

description: The study of rapid neutron capture (r-process) nucleosynthesis is essential for our understanding of the origins of heavy elements. There are challenges, both in the context of nuclear physics and astrophysics that must be overcome in order to better understand the r-process. To further the study of the r-process I have developed software (r-Java 2.0) that aims to help tackle both the nuclear and astrophysical challenges of this field. My thesis is divided into two parts; first focusing on the scope and applicability of r-Java 2.0 and second, exploring possible observational signatures of a proposed r-process site, the quark nova. Part I: Within the first part of my thesis I discuss the capabilities of r-Java 2.0. The ability to solve a full reaction network which incorporates r-process relevant reactions for over 8000 nuclei is compared to an oft-used approximate method. The sophisticated fission algorithm developed into r-Java 2.0 is used to show that the simple maximum nuclear mass approximation for fission that is commonly applied can lead to over-predicting the capabilities of an r-process site. Test cases that were run for r-Java 2.0 whereby I aimed to reproduce the published results from similar full reaction network codes show good agreement and highlight the need for a universal code. I then use r-Java 2.0 to study three proposed astrophysical r-process sites; neutrino-driven wind around proto-neutron stars, ejecta from neutron star mergers and ejecta from quark novae. For each site the effect of varying physical parameters on r-process abundance yield is studied. The final r-process abundance distribution from each site is compared to observations. The neutrino-driven wind is shown to require extreme values of entropy in order to produce heavy (mass number, $A &gt; 190$) elements. The results of my work show that ejecta from neutron star mergers is likely rich in heavy ($A &gt; 190$) elements; however for expansion velocities consistent with hydrodynamic simulations the solar rare-earth peak is not produced. From my work, the ejecta from a quark nova is shown to be a viable source of $A &gt; 190$ nuclei and capable of synthesizing the rare-earth peak. Part II: The astrophysical phenomenon of super-luminous supernovae is studied in the context of quark novae. A selection of eight super-luminous supernovae whose light curves span the range of observed morphologies are compared to the light curve produced by the interaction between a supernova envelope and quark nova ejecta. The length of time between supernova and quark nova explosion is shown to be the key parameter in determining the super-luminous supernova light curve morphology. The success of the quark nova at explaining super-luminous supernovae as well as its robustness as an r-process site hints at its possible existence in nature. The implications of finding a quark nova would be felt across several fields including astrophysics, nuclear physics and QCD physics.