CFD-MHD Project Research Highlights

Simulation of Collapse of Magnetic Molecular Cloud

Anthony Allen has been collaborating with Frank Shu and Z. Li on the collapse of magnetized singular isothermal toroids. Recent improvements in the numerical codes have made it possible to simulate collapse both with and without rotation. Currently, Allen is investigating the possibility of combining wind with collapse, which seems natural given the results of the aforementioned works. In addition, Allen is also simulating the pre-collapse phase of molecular clouds leading to the pivotal state, which leads to gravitational collapse. Another project in progress is the study of the collapse of Toomre-Hayashi Toroids, which are self-similar toroids first studied in the context of galactic dynamics. The fragmentation of these toroids will make a useful starting point into 3D simulations.

Please click on the images for animation!!! Photos and animations courtesy of Winny Chuang

These are momentum 0, 1, and 2 plots for MHD collapse calculations of magnetized, rotating, singular isothermal toroids. Stars are believed to have formed from the collapse of molecular clouds. These clouds are observed to be cold, with weak magnetic fields, and small initial rotation. Realistic models of these clouds have been proposed by Frank Shu (Tsing-Hua U.) and Zhi-yun Li (UVa). These models have been used as initial states for magnetohydrodynamic collapse calculations to study the physics of the early stages of star formation. The momentum-0 plot shows the false-color column density an observer might see if viewing the cloud from a side perpendicular to the axis of rotation. A high density, magnetically supported pseudo disk is present in the mid-plane, but is hard to see with this false-color scheme. The momentum-1 plot shows the velocity profile of the collapsing cloud. Far from the center, the pre-collapse, rotational effects are visible. Closer to the center, one can see slower, magnetically braked material as well as an angular-momentum-carrying outflow. The outflow is driven by the same magneto-centrifugal mechanism believed to be responsible for jets, although it is at much lower velocity than typical jets. This braking mechanism allows for efficient transport of angular momentum from a forming protostar to the outer cloud and is a possible explanation of the angular momentum removal problem in star formation; with magnetic braking, central accretion proceeds at a constant rate allowing growth to stellar mass-scales. The momentum-2 plot shows velocity dispersion in the region.