The coldest clouds in the ISM are molecular clouds, so named because their temperatures are low enough and their densities high enough for atoms to join together into molecules. These clouds are capable of collapsing to form new stars, in a stellar nursery like the one in the left image. The Pleiades (right image) is an example of stars that formed recently within such a nursery.
Molecular clouds range in mass from a few times the mass of our Sun (solar masses) to 10 million solar masses. Individual stars range from 0.08 to about 150 solar masses.
What does all of this imply about how stars form from molecular clouds?