Giant molecular cloud

node · earth · Galactic - throughout the interstellar medium

A cold, dense region of the interstellar medium in which hydrogen exists as H2 rather than as atoms, and the only environment in which stars are known to form. Typical temperatures are around 10 to 20 K and giant complexes contain on the order of ten thousand to a million solar masses of gas and dust spread over tens of parsecs. A cloud does not collapse simply because it is massive: turbulence and magnetic fields provide most of the support on large scales, and thermal pressure dominates only in the densest cores. Collapse begins where a region exceeds the Jeans mass for its temperature and density, which is why star formation is patchy and clustered rather than uniform. Crucially, the cloud is not primordial material: its carbon, oxygen and iron were made inside earlier generations of stars, so every new star is assembled from the debris of dead ones. Not a place on Earth.