Journal Article

Why are most molecular clouds not gravitationally bound?

C. L. Dobbs, A. Burkert and J. E. Pringle

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 413, issue 4, pages 2935-2942
Published in print June 2011 | ISSN: 0035-8711
Published online May 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.18371.x
Why are most molecular clouds not gravitationally bound?

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The most recent observational evidence seems to indicate that giant molecular clouds are predominantly gravitationally unbound objects. In this paper we show that this is a natural consequence of a scenario in which cloud–cloud collisions and stellar feedback regulate the internal velocity dispersion of the gas, and so prevent global gravitational forces from becoming dominant. Thus, whilst the molecular gas is for the most part gravitationally unbound, local regions within the denser parts of the gas (within the clouds) do become bound and are able to form stars. We find that the observations, in terms of distributions of virial parameters and cloud structures, can be well modelled provided that the star formation efficiency in these bound regions is of the order of 5–10 per cent. We also find that in this picture the constituent gas of individual molecular clouds changes over relatively short time-scales, typically a few Myr.

Keywords: hydrodynamics; stars: formation; ISM: clouds; ISM: kinematics and dynamics

Journal Article.  6262 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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