TAP Colloquium

Monday, Apr 14, 2014
4:00 pm — 5:00 pm

Location: Steward Observatory
Room: N210

Xuening Bai
Harvard-Smithsonian Center for Astrophysics

Transport and Accretion Processes in Protoplanetary Disks: A Paradigm Shift

The structure and evolution of protoplanetary disks (PPDs) are largely determined by the process of angular momentum transport, and are key to understanding many aspects of planet formation. Due to extremely weak level of ionization, the gas dynamics of PPDs is largely controlled by non-ideal magnetohydrodynamical effects, including Ohmic resistivity, Hall effect and ambipolar diffusion (AD). The conventional picture considered only the effect of Ohmic resistivity under the framework of magnetorotational instability (MRI) driven accretion, leading to the conclusion of layered-accretion in the inner disk. Via local shearing-box simulations that self-consistently include all three non-ideal MHD effects, we show that the Hall and AD terms each introduces distinct new features that qualitatively change the conventional picture. In particular, in the inner disk around 1 AU, the MRI is completely suppressed due to Ohmic resistivity and AD, with a strong magnetocentrifugal wind launched which efficiently drives disk accretion. In addition, over a wide range of disk radii, the gas dynamics strongly depends on the polarity of the external magnetic field threading the disk, thanks to the Hall effect. In the outer disk, MRI mainly proceeds in the surface layer due to far-UV ionization, while is damped near the midplane due to AD. Our simulation results provide key ingredients for a new paradigm on the transport and accretion processes in PPDs, while a full understanding of PPD gas dynamics requires future global simulations.

Host: Isamu Matsuyama
TAP Colloquia