Computer Science – Sound
Scientific paper
Dec 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999sf99.proc..123n&link_type=abstract
Star Formation 1999, Proceedings of Star Formation 1999, held in Nagoya, Japan, June 21 - 25, 1999, Editor: T. Nakamoto, Nobeyam
Computer Science
Sound
2
Scientific paper
We discuss the widely accepted assumption that low-mass stars form mostly in magnetically subcritical cloud cores and high-mass stars form in magnetically supercritical ones. We show on some physical considerations that cloud cores are mostly magnetically supercritical. In a magnetically supercritical core there is a critical value Pcr for the pressure of the surrounding medium Ps, above which the core cannot be in magnetohydrostatic equilibrium and has no choice but to collapse; Pcr depends sharply on the core mass, the effective sound velocity in the core which includes the effect of turbulence, and the effective coefficient for the gravity diluted by magnetic force. The cloud core begins dynamical contraction when Pcr has become smaller than Ps by some mechanisms. Dissipation of turbulence is the most important process of reducing Pcr. Therefore, in most cases the timescale of star formation in each core is the dissipation time of turbulence, which is several times the free-fall time of the core. However, the timescale of converting molecular gas into stars is about 102 times the free-fall time because star formation efficiency in each core is only a few percent.
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