3-D Stellar Hydrodynamics Simulations for Convective-Reactive Nucleosynthesis

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Astronomical observations are now probing the early stages of the universe, in which galaxies developed and merged, and the formation of structure in the universe and its evolution to the present era was set in motion. An important part of this story is the chemical evolution of galaxies. The formation of the elements in stars and their subsequent dispersal are powerful tracers of structure formation and evolution. This project will simulate on Blue Waters processes deep inside stars that play an important role in the heavy elements they generate. These processes are driven by mixing of gases at the boundaries of convection zones, which can bring new fuels into a convection zone, carrying them down into much hotter regions where they burn very rapidly and activate nuclear reaction networks in a special convective-reactive regime. In this regime, reacting nuclei are transported by the turbulent convection flow on about the same timescale as the reactions take place, so that significant departures from spherical symmetry, even in a statistical sense, can result. This project will use the petascale capabilities of Blue Waters to simulate these brief events in 3D.This project we will build on earlier work on Blue Waters to study a process where the O-shell convection zone in a massive star can work its way to the base of the C-shell convection zone above, leading to ingestion of carbon fuel and an ultimate merger of the two burning shells. The project will compute the resulting nucleosynthesis by following the concentrations of a large number of nuclear isotopes and computing their interactions on a 4-D grid of reduced resolution in space and time. A fine grid is required to accurately advance the turbulent convection flow and to compute the amount of fuel entrained in it at the convection zone boundary. The study will follow the most important species on this fine grid, but will represent on the coarser grid the large number of nuclear reactions from which energy release is minor and has minimal back reaction on the flow. This project will generate a large database of results from the 3-D simulations on Blue Waters of convective boundary mixing in stellar interiors. The project intends to organize this database so that the simulation codes can mine it automatically, comparing it to a variety of potentially useful 1-D models of the mixing process. In terms of broader impacts, the project will make this database and tools available to the community on-line in a useful format, so that it will enable research by many others. In addition, the project will work with the NuGrid collaboration to see that the results are incorporated into data sets that are available to the community for chemical evolution simulations of galaxies and structures in the early universe.