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Project Progress

This year we made great progress on quantifying how well an exploding supernova could inject material into nearby molecular clouds that are forming protostars. This was the major goal of Task 3 and we are happy to finally have some definite answers. The research resulted in 2 conference abstracts and culminated in the refereed publication, “Mixing of Clumpy Supernova Ejecta into Molecular Clouds”, by Liubin Pan, Steve Desch, Evan Scannapieco and Frank Timmes. A figure from that paper is found below. We carried out state-of-the-art adaptive-mesh-refinement hydrodynamic simulations of how a clump of supernova material would interact with a molecular cloud, using the FLASH code run on thousands of processors at the Arizona Center for Advanced Computing. AWe generally conclude that supernova material in will not mix into a molecular cloud unless it is clumpy, but that if the density structure of the ejecta resembles the clumpy Cassiopeia A supernova remnant ejecta, then the clumps, or “bullets” of supernova material will penetrate mix in the molecular cloud, to depths ~ 0.5 pc. The high ejecta velocities and broad range of relevant lengthscales made these calculations technically very challenging. Cooling instabilities that fragment the material were found to be very important, hindering numerical convergence and complete validation of the results. But we can state with confidence that supernova material will mix into nearby molecular clouds, so that all stars forming late (> 4 Myr) into the lifetime of a massive cluster will be contaminated with supernova material at a mass fraction ~ 10^-4. This is exactly the shift needed to explain the abundances of short-lived radio-nuclides like ²⁶Al. We are now trying to assess the shifts in stable isotopes due to supernova injection.