Star formation

Dense cores are the smallest and densest types of molecular clouds. They are particularly significant as being the birthplaces of both single and binary stars. A large fraction of dense cores, in fact, already contain young stars. Many of the rest exhibit a slow, inward contraction, which could be the prelude to the full collapse that results in star formation. Both types of dense cores have temperatures near 10 K. They are slowly rotating, and appear elliptical when seen in projection onto the sky. In three-dimensional space, they are prolate spheroids or perhaps more complex, triaxial configurations.

The Milky Way, like other spiral galaxies, contains both stars and more rarefied, interstellar gas. About half the mass of this material is in molecular clouds, so called because they are chiefly made of hydrogen molecules. Molecular clouds have a wide range of sizes and masses. They are not uniform, but contain nested substructures. The...