Self-Regulated Star Formation in Molecular Clouds

Abstract

It is now known that molecular clouds are the sites of star formation in the Galaxy. Forty years ago, however, it was not clear that molecules were even an important constituent of the Galaxy. In 1955, Townes [1] presented a paper at IAU Symposium 4 in which he listed a number of molecules that might have radio transitions. Thirteen years after this conference, Townes and his collaborators [2] discovered the first polyatomic molecule in interstellar space, NH₃. Now, with more powerful radio telescopes, ammonia is used to trace regions in which low mass stars are forming. Many of the molecules Townes listed in his 1955 talk have been discovered, along with an even larger number of other molecules. From observations of these molecules, particularly CO, we have learned an enormous amount about the conditions under which molecules can exist in the interstellar medium. Here we consider how these conditions lead to the formation of low-mass stars, and how this star formation in turn governs the structure of the molecular clouds in which most molecules are embedded. A fuller account of this work will be given elsewhere [3].