Cloud Dissipation and Disk Wind in the Late Phase of Star Formation

TL;DR

This study uses long-term 3D non-ideal MHD simulations to explore the evolution of star and disk formation, revealing disk dissipation, wind revitalization, and mass ejection processes over 150,000 years.

Contribution

It provides new insights into late-stage disk evolution, wind revitalization, and the timescale of disk dissipation after envelope dispersal.

Findings

Disk size grows to over 300 au after envelope dispersal.

Approximately 30% of initial cloud mass is ejected by outflows.

Disk wind persists until the end of the simulation, driven by magnetic pressure.

Abstract

We perform a long-term simulation of star and disk formation using three-dimensional non-ideal magnetohydrodynamics. The simulation starts from a prestellar cloud and proceeds through the long-term evolution of the circumstellar disk until $\sim 1.5\times10^5$ yr after protostar formation. The disk has size $\lesssim 50$ au and little substructure in the main accretion phase because of the action of magnetic braking and the magnetically-driven outflow to remove angular momentum. The main accretion phase ends when the outflow breaks out of the cloud, causing the envelope mass to decrease rapidly. The outflow subsequently weakens as the mass accretion rate also weakens. While the envelope-to-disk accretion continues, the disk grows gradually and develops transient spiral structures due to gravitational instability. When the envelope-to-disk accretion ends, the disk becomes stable and reaches a size $\gtrsim 300$ au. In addition, about 30% of the initial cloud mass has been ejected by the outflow. A significant finding of this work is that after the envelope dissipates, a revitalization of the wind occurs, and there is mass ejection from the disk surface that lasts until the end of the simulation. This mass ejection (or disk wind) is generated since the magnetic pressure significantly dominates both the ram pressure and thermal pressure above and below the disk at this stage. Using the angular momentum flux and mass loss rate estimated from the disk wind, the disk dissipation timescale is estimated to be $\sim10^6$ yr.