EPoS Contribution
EPoS Contribution
Protostellar Disk Formation in Magnetized Cloud Cores Enabled by Turbulence-Induced Pseudodisk Warping

Zhi-Yun Li
U Virginia, Charlottesville, US
It is well known that the collapse of a non-turbulent molecular cloud core with a dynamically important magnetic field aligned with the rotation axis produces a dense, flattened, equatorial structure - a pseudodisk. The pseudodisk is the conduit through which most of the protostellar core accretion occurs. It plays a key role in the so-called "magnetic braking catastrophe," where the formation of rotationally supported disks is suppressed in dense cores magnetized to the typically observed levels. We show that this important structure can be strongly warped, but not completely destroyed, by a subsonic or sonic turbulence. The turbulence-induced warping decreases the rates of angular momentum removal from the pseudodisk by both the magnetic torque and magneto-rotationally driven outflow, making it easier to form a rotationally supported disk. Just as importantly, the warping reduces the amount of vertical magnetic flux that is accumulated in the disk-forming region close to the central object, further promoting disk formation. We conclude that the pseudodisk warping is the key to the turbulence-enabled disk formation in magnetized dense cores. It is also crucial to the disk formation enabled by a misalignment between the magnetic field and rotation axis. These two previously established, distinct scenarios of disk formation are thus unified. We find that the disks formed in turbulent magnetized cores are rather thick and significantly magnetized. Implications of these findings, particularly for the thick young disk inferred around the protostar L1527, will be discussed.
Caption: 3D structure of the warped pseudodisk. Plotted are isodensity surfaces at ρ=10-17 (red surfaces) and 10-16gcm-3 (blue) for a turbulent Mach number M=0.3 (left panel) and 1 (right) case at a representative time. Note the corrugation of the pseudodisk (as traced by the red surfaces) induced by turbulence. The blue region roughly corresponds to the rotationally supported disk in the right panel (with M=1). The box size is 1200 AU on each side.
Collaborators:
R. Krasnopolsky, ASIAA, Taiwan
H. Shang, ASIAA, Taiwan
B. Zhao, U. of Virginia, USA
Suggested Session: Cores to Disks