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P.S. Li (NCSA), M.L. Norman (UCSD), F. Heitsch (MPIA), M.-M. Mac Low (AMNH)
Observations of molecular clouds in our Galaxy indicate that the star formation rate is orders of magnitude below expectations from simple gravitational collapse arguments. Magnetostatic pressure or magnetohydrodynamic (MHD) waves are suggested to counteract the gravitational force and support the molecular clouds from collapsing (e.g. Mouschovias & Spitzer 1976, McKee 1999).
Here we report the continuing numerical study of the gravitational collapse of magnetized molecular clouds driven by supersonic, gasdynamial turbulence (Heitsch, Mac Low, & Klessen 2001) using the newly released ZEUS-MP code on 2563 and 5123 grids. The resolution is high enough to resolve shorter wavelength MHD waves which clearly delay gravitational collapse. In the late stage of the simulations, when gravitational effect becomes stronger, we observe 12 disk-like cores out of total 35 cores forming in dense gas regions in the 5123 run compared to 4 disk-like cores out of total 10 cores in the 2563 run.
Using low density scaling (n(H2) \approx 102 cm-3 and T \approx 10K), the masses of disk-like cores are in the range of 1.8 M\sun to 10.8 M\sun. The disks are centrifugally supported with a mass accretion rate of 10-7 M\sun yr-1to a few of 10-6 M\sun yr-1. Although the presence of the supersonic turbulence in the simulations will disrupt the process of core formation, we find that the scaling relation Bc \propto \rhoc1/2 (Mouschovias 1991) is obeyed in 80% of the disk-like cores. All the cores are studied before they violate the TrueLove criterion (TrueLove et al. 1997).
This work is partially supported by NSF grant PHY 99-79985. The simulations are performed at NCSA using Cray/SGI Origin 2000.
The author(s) of this abstract have provided an email address for comments about the abstract: pakshing@ncsa.uiuc.edu