Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...209.1715h&link_type=abstract
2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #17.15; Bulletin of the American Astronomical Society, V
Astronomy and Astrophysics
Astronomy
1
Scientific paper
The structural richness of molecular clouds and their observed linewidths indicate that they are highly dynamical. Observations suggest (a) that local star formation in such clouds is generally "rapid", i.e. it happens within a few (1-3) free-fall times, and (b) that the parent molecular clouds are short-lived. Numerical models have helped to identify turbulent fragmentation as one of the main agents for rapid star formation. However, turbulence often has been claimed to lend support to the parent molecular cloud, rendering star formation seemingly "slow". A solution to this conundrum requires understanding the initial conditions of star formation in a broader frame, i.e. a closer look at the details of molecular cloud formation. We conducted several numerical experiments, all centered on the scenario of molecular cloud formation in colliding flows (Balleteros-Paredes et al. 1999, ApJ, 527, 285; Hartmann et al. 2001, ApJ, 562, 852, Heitsch et al. 2006, ApJ 648, 1052) in the context of rapid star formation.
We find (1) that turbulence is a natural consequence of the formation process of the clouds, due to a combination of strong thermal and dynamical instabilities, and we give an analytical prediction for the relative importance of the instabilities in various regimes. (3) Initial conditions in the flows and the flow geometry play a crucial role for the structure of the resulting molecular cloud. (2) Stars begin locally to form immediately once sufficient cold dense gas is available. Thus, the local age spread of the stars is expected to be small. (3) Magnetic fields can play a dynamically important role, but generally do not prevent fragmentation, and are generally too weak to prevent gravitational collapse.
Burkert Andreas
Devriendt J. E.
Hartmann Lee
Heitsch Fabian
Slyz Adrianne D.
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