Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aspc..417..243f&link_type=abstract
Submillimeter Astrophysics and Technology: a Symposium Honoring Thomas G. Phillips ASP Conference Series, Vol. 417, proceedings
Astronomy and Astrophysics
Astrophysics
Scientific paper
Molecular clouds are turbulent flows with comparable turbulent and magnetic internal energy densities at large scale. Jointly, turbulence and magnetic fields balance their self-gravity. Hence, dissipation of turbulence and/or decoupling of matter from magnetic fields are critical processes in the early steps of star formation in molecular clouds. Turbulence is known to be intermittent in space and time in laboratory and atmospheric flows. Interstellar turbulence may be intermittent as well, with characteristics modified by compressibility and magnetic fields. We report here the results of a two-decade effort, shared with T. G. Phillips and several others, to find and characterize the rare and tiny regions where turbulent dissipation is concentrated in molecular clouds. These appear to be organized into thin parsec-scale coherent structures of intense velocity-shears in the three translucent fields where they have been sought. The values of velocity-shears found at the milliparsec-scale are large, up to 800 km/s/pc, and suggest dissipation rates that are locally several orders of magnitude above average. The short timescales (and/or large gas accelerations) involved, ˜3× 103 yr, are commensurate to many inelastic collision timescales in gas of moderate density. Thus, gas dynamics in these structures not only affect chemistry, with even a possible causal relation between intense velocity-shears and molecule formation in the cold neutral medium, but also modify the coupling of the gas to dust grains and to magnetic fields. These results open a new window on turbulent dissipation, its impact on small-scale gas dynamics and its role in the formation of dense cores in molecular clouds.
Falgarone Edith
Hily-Blant Pierre
Pety Jérôme
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