The electromagnetic interaction of these spinning particles produces a force which involves energy. The lowest energy state of the atom is when the two spins are anti-aligned. Using the 21 cm line we find that neutral H is concentrated in the plane of the galaxy. Molecular Clouds Molecules are collections of atoms bound together by electromagnetic forces. IR An amazing array of molecules have been discovered in space.
Molecules only form in cold dense places.
These are called Molecular Clouds. In this picture the red and yellow lines are contours of emission from different kinds of molecules. The contours are superimposed on top of an optical image of a new born star and its HII region Most of the ISM mass is in these clouds. The come in a hierarchy of forms. These clouds are where stars are known to form.