CDS&E: 3-D Stellar Hydrodynamics of Convective Boundary Mixing and Shell Mergers in Massive Stars

University Of Minnesota-Twin Cities, Minneapolis MN

Investigators

Abstract

The evolution of stars and their ultimate fate as white dwarfs, white dwarf supernovae, neutron stars, or black holes remains at the center of research in astronomy. This question relates to diverse research topics in time domain astronomy, supernova research, nuclear astrophysics, galactic chemical evolution, asteroseismology, stellar populations, and the formation and evolution of stars and structure in the early universe. However, the fundamental macroscopic stellar physics process of convection remains poorly understood. Although there is some good theory, surprisingly accurate despite being rather simplistic, realistic studies must rely on computationally intensive simulations. That is what this project will enable, and perform. It will have a large impact on stellar evolution theory, providing cutting edge techniques and innovative methods of wide applicability. The study supports one graduate and up to three undergraduate students, and the results will be used in course teaching. The details, especially the study of mergers of convective shells, such as the C- and O-burning shells of massive stars, as well as convective boundary mixing, can only be realistically captured in complex three-dimensional (3D) hydrodynamics simulations. This project will build on prior work to pursue three main objectives: (1) validation of a 1D model of convective boundary mixing, using brief 3D stellar hydrodynamics simulations relevant to massive stars near the ends of their lives; (2) assessment of when two convective shells right on top of each other can in fact merge, using the model from (1) combined with 3D simulation; and (3) for shell merger cases, use 3D hydrodynamical simulations to study when nearby shells exchange their chemical abundance mixtures. Prior studies in 1D indicate that the convection zone above the O-burning shell could incorporate enough material from above it to reach the C-burning shell. This could cause odd-Z elements like potassium, scandium, and chlorine to be produced in greater abundance. A sequence of brief 3D simulations alternating with longer 1D simulations will show in detail the approach to, and ultimate result of, the shell merger process. The large database of results on convective boundary mixing will be organized and made available, together with the tools that mine it, analyze it, and display its results, to enable unanticipated research by the greater community. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.