Gravitationally Contracting Clouds and Their Star Formation Rate

Abstract

We present evidence that giant molecular clouds may be in overall contraction, and we show, by both numerical and semi-analytical arguments, that before they collapse significantly as a whole and transform so much of its mass in stars, the feedback from massive stars produced by first local collapses, regulates the fraction of mass that continues forming stars at values consistent with those observed. Moreover, we have found that the gravitational collapse time for non-spherical structures is longer that the standard free-fall time for spherical ones of the same volume density by a factor ∼ $\sqrt{ A}$, where A is the aspect ratio of the structure. This implies that clumps inside filaments collapse earlier, naturally giving rise to the ubiquitously observed pattern of clumps within accreting filaments, and that the free-fall estimate for the Galactic SFR may have been overestimated, if clouds in general have non-spherical symmetry.