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Astronomy Seminar: Gas Dynamics in Protoplanetary Disks: Putting Accretion Theory to the Test

Oct 23, 2020 - 4:10 PM
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Dr. Jacob Simon, Iowa State


It is still uncertain what exactly is responsible for driving angular momentum transport in protoplanetary disks, thus setting the environment in which planets are born. This transport may find its origin in turbulence driven by the magnetorotational instability (MRI), magnetically driven winds that remove angular momentum vertically, or some combination of both. In this talk, I first present a series of high-resolution numerical simulations that were designed to address this issue and make testable predictions. I will then describe observations made with ALMA to directly test these predictions by measuring the turbulent broadening of molecular lines that probe the outer regions of protoplanetary disks. These results, coupled with other recent studies, suggest that for most disks, turbulent angular momentum transport is considerably weaker than originally predicted, at least for scales of 30-100 AU and beyond. I will then describe how even in the presence of magnetically driven winds, non-negligible turbulence (well above the observational upper limit) is still present unless very specific criteria are met. These considerations strongly motivate the development of a new model for protoplanetary disk accretion, and I will conclude with a discussion of the implications of this new model, both within the context of theoretical studies and observational campaigns. Ultimately, continuing to combine high-fidelity numerical simulations with state-of-the-art observations will be essential to understanding how angular momentum transport is driven in protoplanetary systems