Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21343904h&link_type=abstract
American Astronomical Society, AAS Meeting #213, #439.04; Bulletin of the American Astronomical Society, Vol. 41, p.314
Astronomy and Astrophysics
Astronomy
Scientific paper
Molecular cloud lifetimes are still a matter of debate. Are molecular
clouds long-lived in the sense that they live for several free-fall times, being supported by turbulence and/or magnetic fields, or are they short-lived, i.e. do they live only for a few free-fall times, being dispersed by feedback from their stars? In the first case, it has been shown that the turbulence needs constant replenishment, in Taurus-like clouds possibly by winds and outflows of low-mass stars. There is considerable observational evidence from solar-neighborhood clouds for the second case, indicating that star formation sets in rapidly after cloud formation, and that these clouds do not live for much longer than 5 Myr, or 2-3 free-fall times.
Recent models of molecular cloud formation driven by large-scale flows sweeping up material have identified a combination of thermal and dynamical instabilities allowing the rapid fragmentation of the forming cloud necessary for the rapid onset of localized star formation before global gravity effects can dominate the cloud evolution. However, in the absence of energetic feedback such as HII regions or supernovae, these clouds are eventually bound to collapse globally, resulting in unrealistically high star formation rates.
We argue that nearby B-stars from earlier star formation epochs will eventually seal the fate of clouds like Taurus. We discuss the average distance between B-stars and clouds in the Milky Way, and we demonstrate with numerical models the effect of a supernova explosion on a nearby Taurus-like cloud, determining the critical distance at which the cloud will be disrupted.
FH is supported by NSF grant AST 0807305.
Hartmann Lee W.
Heitsch Fabian
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