Dust Settling and Instability in Stratified Protostellar Disks
First Author:
David Tilley
Email: user AT xxx.eduu
University of Notre Dame
Department of Physics
225 Nieuwland Science Hall
Notre Dame, IN 46556 USA
Abstract
The early stages of planet formation occur in a disk that contains a mixture of dust grains of various sizes with the gas. The mutual interactions between dust and gas can alter the rate at which grains can grow into pebble and boulder-sized objects through the formation clumps in which the density of dust is greatly enhanced. To understand how this clumping develops in a stratified protostellar disk, we perform a suite of 3D shearing box simulations that model parcels of a minimum-mass solar nebula at radii of 0.3-100 AU. We examine the structure of several initially well-mixed layers of dust of different sizes as they simultaneously interact with the gaseous disk, which is turbulently driven via the magnetorotational instability (MRI). We find that large dust grains settle into a thin layer where they are subject to a streaming instability that leads to large enhancements in dust density, while smaller dust grains can remain well-mixed with the gas. We characterize the vertical distribution of the dust of different sizes at different radial positions in the disk. We contrast these results for a minimum-mass solar nebula model to one in which the gas has been depleted by a factor of twenty, while the dust density has remained unchanged -- as might be found in a more evolved disk. In these latter models, feedback from the dust on the gas has a stronger effect on their mutual evolution.
