CCA Colloquium: Bruce Draine

Title: A New Model for Interstellar Dust: “Astrodust” + PAHs

Abstract: Observations strongly suggest that interstellar dust in the Milky Way consists predominantly of a single composite material, which we term “astrodust”. “Astrodust” has a substantial silicate fraction, but also contains carbonaceous compounds. The effective dielectric function characterizing this material can be inferred from astronomical observations. While astrodust must be somewhat porous, the porosity is limited by observations of starlight polarization and polarized submm emission. Models with highly porous grains are not viable. In addition to the astrodust grains a large population of polycyclic aromatic hydrocarbon (PAH) nanoparticles is also present in normal star-forming galaxies. The astrodust+PAH model is tested by many observational constraints. The ratio of 10um polarization to V-band starlight polarization is predicted. The processes required to produce and maintain the astrodust and PAH population in the ISM will be discussed

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