giant molecular cloud

A giant molecular cloud (GMC) is a molecular cloud (i.e., including compounds such as molecular hydrogen, aka HH or H₂), with a mass on the order of 10³ to 10⁷ solar masses. They are a common place for star formation, within subregions that cool and contract further. Bound GMCs (gravitationally bound) are observed, but most appear to be unbound. An area of research is how gravitationally bound volumes that become stars manage to form within an unbound GMC.