Dust Motion and Possibility of Dust Growth in a Growing Circumstellar Disk

TL;DR

This study uses 3D resistive magnetohydrodynamics simulations with dust particles to explore dust motion and growth potential in early circumstellar disks, revealing size-dependent ejection and survival patterns that influence planet formation zones.

Contribution

It provides new insights into dust dynamics during star formation, especially how dust size affects ejection and survival, impacting planet formation regions.

Findings

Small dust grains are ejected by outflows, large grains tend to remain.

Dust grains in the outer disk can survive and grow, favoring planet formation.

Dust motion behavior divides into two trends after settling in the disk.

Abstract

We calculate the evolution of a star-forming cloud core using a three-dimensional resistive magnetohydrodynamics simulation, treating dust grains as Lagrangian particles, to investigate the dust motion in the early star formation stage. We prepare six different-sized set of dust particles in the range $a_{\rm d}=0.01$--$1000\,\mu$m, where $a_{\rm d}$ is the dust grain size. In a gravitationally collapsing cloud, a circumstellar disk forms around a protostar and drives a protostellar outflow. Almost all the small dust grains ($a_{\rm d} \lesssim 10$--$100\,\mu$m) initially distributed in the region $\theta_0 \lesssim 45^\circ$ are ejected from the center by the outflow, where $\theta_0$ is the initial zenith angle relative to the rotation axis, whereas only a small number of the large dust grains ($a_{\rm d} \gtrsim 100\,\mu$m) distributed in the region are ejected. All other grains fall onto either the protostar or disk without being ejected by the outflow. Regardless of the dust grain size, the behavior of the dust motion is divided into two trends after dust particles settle into the circumstellar disk. The dust grains reaching the inner disk region from the upper envelope preferentially fall onto the protostar, while those reaching the outer disk region or disk outer edge from the envelope can survive without an inward radial drift. These surviving grains can induce dust growth. Thus, we expect that the outer disk regions could be a favored place of planet formation.