Dust Dynamics in Transitional Disks: Clumping and Disk Recession

TL;DR

This paper demonstrates that non-axisymmetric dust clumping caused by an instability at the inner edge of transitional disks, combined with radiation pressure, can lead to outward dust migration and cavity formation.

Contribution

It introduces a new non-axisymmetric instability mechanism that influences dust dynamics and cavity formation in transitional disks, using two-dimensional simulations.

Findings

Dust clumping creates high-density features allowing radiation leakage.

Radiation pressure and shadowing can cause net outward dust migration.

Inner disk recession speeds can reach up to 10^{-5} times Keplerian speed.

Abstract

The role of radiation pressure in dust migration and the opening of inner cavities in transitional disks is revisited in this paper. Dust dynamics including radiation pressure is often studied in axisymmetric models, but in this work, we show that highly non-axisymmetric features can arise from an instability at the inner disk edge. Dust grains clump into high density features there, allowing radiation to leak around them and penetrate deeper into the disk, changing the course of dust migration. Our proof-of-concept, two-dimensional, vertically-averaged simulations show that the combination of radiation pressure, shadowing, and gas drag can produce a net outward migration, or recession, of the dust component of the disk. The recession speed of the inner disk edge is on the order of $10^{-5}$ times Keplerian speed in our parameter space, which is faster than the background viscous flow, assuming a Shakura & Sunyaev viscosity alpha $\lesssim 10^{-3}$. This speed, if sustained over the lifetime of the disk, can result in a dust cavity as large as tens of au.