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Magnetohydrodynamics
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.
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Please
click for animation!!!
Photos and animations courtesy of Winny Chuang. |
Figure
3: 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.
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Contents Copyright 1999-2003 CFD-MHD at ASIAA
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