Differential metal enrichment and dust synthesis in the aftermath of supernova explosions




Sluder, Alan

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Emerging from the Big Bang, the Universe contained hydrogen, helium, and lithium. Heavier elements were synthesized in stars and stellar explosions. The first stars formed when the Universe was about a hundred million years old and exploded to scatter their newly-minted elements into space. Elements such as carbon and iron polluted the protogalactic gas clouds from which new stellar generations would form. Low mass stars dating from this early chemical enrichment have survived in the Galaxy as a fossil record of the young Universe. The formation of low-mass stars requires dust grains but dust synthesis is still incompletely understood. I investigate two questions central to the role of stellar explosions in the transformation of the Universe: how the measured variation in ancient stellar chemical abundance patterns relates to the complex hydrodynamics of stellar explosions---the supernovae, and how stellar explosions synthesize the dust that is necessary for low-mass star formation. First, I use high performance computing to model the aftermath of a supernova in an ancient cosmic dark matter halo. Tracing the transport of individual nucleosynthetically-enriched mass elements from their explosion site through the subsequent gravitational compression and collapse, I quantify how the complex hydrodynamics skews the chemical abundances in the collapsed gas from the explosion's gross elemental yields. I find that a portion of the measured variation in elemental abundance ratios in ancient low-mass stars can be ascribed to specific hydrodynamic effects. Second, I use chemical and kinetic calculations to study how, during the first three decades, gas-phase elements in supernova ejecta aggregate into solid dust grains. I compute the grains' chemical composition, size distribution, and mass yield. My model takes into account the effects of ejecta radioactivity, the lack of thermal coupling between gas and dust, and grain electric charge. The model incorporates non-equilibrium chemical reactions that produce atomic and molecular clusters, grain growth by accretion and coagulation, and grain destruction by evaporation and oxygen and noble gas ionic weathering. I find that a large fraction of refractory elements can be incorporated into grains with size distribution resembling that in the nearby supernova SN 1987A.



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