DUST CAPTURE AND LONG-LIVED DENSITY ENHANCEMENTS TRIGGERED BY VORTICES IN 2D PROTOPLANETARY DISKS

Abstract

We study dust capture by vortices and its long-term consequences in global two-fluid inviscid disk simulations using a new polar grid code RoSSBi. We perform the longest integrations so far, several hundred disk orbits, at the highest resolution attainable in global disk simulations with dust, namely, 2048 × 4096 grid points. We vary a wide range of dust parameters, most notably the initial dust-to-gas ratio ϵ varies in the range of 10 −4 –10 −2 . Irrespective of the value of ϵ , we find rapid concentration of the dust inside vortices, reaching dust-to-gas ratios of the order of unity inside the vortex. We present an analytical model that describes this dust capture process very well, finding consistent results for all dust parameters. A vortex streaming instability develops, which invariably causes vortex destruction. After vortex dissipation large-scale dust rings encompassing a disk annulus form in most cases, which sustain very high dust concentration, approaching ratios of the order of unity; they persist as long as the duration of the simulations. They are sustained by a streaming instability, which manifests itself in high-density dust clumps at various scales. When vortices are particularly long-lived, rings do not form but dust clumps inside vortices can survive a long time and would likely undergo collapse by gravitational instability. Rings encompass almost an Earth mass of solid material, while even larger masses of dust do accumulate inside vortices in the earlier stage. We argue that rapid planetesimal formation would occur in the dust clumps inside the vortices as well as in the post-vortex rings.