Oral Presentation
The formation of rings and gaps in magnetized wind-launching disks
Presenter: Scott Suriano (The University of Tokyo)
Radial substructures in disks around young stellar objects are now routinely detected by state-of-the-art observational facilities. There is also growing evidence that magnetic disk winds drive accretion in such disks. We investigate the formation of radial substructures, i.e., rings and gaps, in the outer regions of protoplanetary disks where ambipolar diffusion (AD) is the dominate non-ideal MHD effect. In 2D axisymmetric simulations, we find that disks which are moderately well-coupled to the magnetic field remain relatively laminar, with a radial electric current density that is steepened by AD into a thin layer near the midplane. The toroidal magnetic field sharply reverses polarity in this current sheet, generating a large magnetic torque that drives fast accretion. The poloidal magnetic field is dragged inward through this accretion layer into a highly pinched radial configuration. The reconnection of this pinched field creates magnetic loops where the net poloidal magnetic flux (and thus the accretion rate) is reduced, yielding dense rings. Neighboring regions with stronger poloidal magnetic fields accrete faster, forming gaps. We extend these 2D simulations to three dimensions and find that rings and gaps still develop naturally in 3D from the same basic mechanism: namely, the redistribution of poloidal magnetic flux relative to disk material from the reconnection of sharply pinched poloidal magnetic field lines. Non-axisymmetric variations arise spontaneously at later times, but they do not grow to such an extent as to disrupt the rings and gaps. These disk substructures persist for up to 3000 orbital periods at the inner edge of the simulated disks, making them attractive sites for trapping large grains that would otherwise be lost to rapid radial migration.
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