A local dwarf galaxy, NGC 5253, has a young star cluster that provides an example of highly efficient star formation. CfA astronomer Jun-Hui Zhao and his colleagues used the Submillimeter Array (SMA) to study the molecular gas (carbon monoxide, CO) at the center of this galaxy in a source called "Cloud D". Usually astronomers use the intensity of the CO radiation to estimate the total gas mass, but this can be a misleading measure since it requires knowing the relative amount of CO to the total material. The team instead used the motions of the gas to infer the total mass present; they used the amount of ultraviolet light to determine the number of stars. The scientists report that their technique is a much more reliable way of measuring the star formation rate.
The astronomers, writing in the latest issue of Nature, find that when they apply their method to the hot, dense and dusty Cloud D, they find a star-formation efficiency exceeding 50%. They note that their SMA images show a streamer of molecular gas falling into the galaxy toward this cloud, and they argue that this infalling material (about two million solar masses of gas) could compress the cloud and thereby induce the dramatic star formation efficiency seen. The new paper also suggests that a similar kind of infall and compression mechanism might have enabled comparably higher star formation rates at earlier times in cosmic history.