“Modeling interstellar dust”
Interstellar dust has long been modeled with separate silicate and graphite/amorphous carbon components. In this talk, I will argue that initially distinct populations of carbonaceous and silicate stardust get rapidly homogenized in the interstellar medium (ISM) into a composite material (“astrodust”). I will demonstrate that the astrodust+PAH model is compatible with current observational constraints on dust extinction and emission in the diffuse ISM, and that it provides a more natural explanation for the observed polarized emission than do two-component models. I will discuss implications for the lifecycle of dust in galaxies and highlight the power of future polarimetric observations on platforms like the PRIMA far-infrared probe to illuminate the formation and evolution of dust. Finally, I will turn to polycyclic aromatic hydrocarbons (PAHs) and give a preview of surprising new results indicating that PAHs are growing rapidly in translucent clouds through accretion of gas-phase carbon atoms.