Collaborative Research: Turbulence and Dynamics of Stars

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This award will support a two-pronged attack on the problems of understanding supernova progenitors and of the physics of supernovae up to and immediately after the explosion. The first project, to be led by Dr. Arnett of the University of Arizona, will model the late evolutionary phase preceding iron core collapse (Type II supernovae) in massive stars. This will be the first time that such calculations have been done in three spatial dimensions, and will cover evolution to the onset of core collapse including an evaluation of the role played by rotation and other mechanisms of symmetry breaking. This epoch is characterized by a complex interplay between turbulence and nuclear burning that determines the entropy and density structure of the pre-collapse core, which along with rotation are important characteristics in determining the outcome of the core-collapse event. The second effort, led by Dr. Starrfield of Arizona State University, will explore accretion onto white dwarfs using compositions ranging from pure helium to a mixture with varying abundances of heavy elements. The goal of this work is to determine the initial conditions that lead either to a Supernova Type Ia explosion, an energetic helium flash, or helium novae. This work is motivated by the inconvenient situation that the kind of star producing Type Ia supernovae is still unknown, and both theoretical and observational arguments for and against various scenarios have only grown more complicated in recent years. Common to both projects is a numerical code that includes a new theory of turbulent convection in three-dimensions that includes good resolution in both spatial dimensions and in time. The project is expected to impact the wider astrophysical community through the release of stellar evolution and convection codes. The project will also support the training of students and a postdoctoral fellow, and the results of this work will be incorporated into the curricula at both institutions.