Rethinking the Nature of Interstellar Dust

Abstract: Observations of the highly polarized emission from Galactic dust have challenged our basic assumptions about the makeup of interstellar grains. In the first part of this talk, I will introduce a new model of interstellar dust that, unlike most dust models of the last four decades, posits that the silicate and carbonaceous materials largely reside on the same grains, an idealized mixture we term astrodust. I will demonstrate the compatibility of the astrodust-based model with existing observations from the UV to the microwave and highlight how it can be tested with future data such as from CCAT-Prime, the Simons Observatory, and LiteBIRD. In the second part of the talk, I will discuss new insights into the relationships between Galactic dust, gas, and magnetic fields, in particular how HI emission can be used to predict dust extinction, emission, and polarization in 3D. I will emphasize throughout the importance of, and implications for, Cosmic Microwave Background polarization experiments, which produce exquisite maps of dust polarization in pursuit of inflationary B-modes.