UNC-CH Physics and Astronomy Master’s Defense

Taylor Stevenson

“Evolution of kilonova ejecta: multifluid gas-kinetic schemes for extreme flow conditions”

The origin of the r-process elements—some of the heaviest metals in our universe, which compose our physical reality—is still unknown. Over the last decade, both observations and numerical models have challenged the belief that core-collapse supernovae are the only source of these elements. An alternative source is provided by binary neutron star mergers. Old stellar populations show strong variations in r-process element abundances, and numerical models of kilonovae remnants predict that ejecta will have different chemical compositions depending on their direction of ejection. Therefore, one possible explanation for the abundance variations is that these chemically different ejecta might not mix completely in the kilonova remnant. I will develop numerical models of mixing within kilonova ejecta to explore this. Such models are challenging since the ejecta evolve over at least 13 orders of magnitude in spatial scale. Additionally, the initial mass density contrast between the ejecta and ambient interstellar medium is ~30 orders of magnitude. To address these challenges, I have implemented a gas-kinetic solver into the computational hydrodynamics code Athena++. I will discuss the concept and method of gas-kinetic solvers and compare them to standard Riemann solvers, and I will present tests of my implementation, including blast wave expansion into a vacuum

This defense will be held remotely via Zoom: https://unc.zoom.us/j/95900765239?pwd=aDJXVTlNeWZZL1dYT1JCSC9XVTVrQT09