Giant Molecular Clouds

Giant Molecular Clouds, or GMCs, are massive clouds of gas in interstellar space composed primarily of hydrogen molecules (two hydrogen atoms bound together), though also containing other molecules. These clouds can contain enough mass to make several million stars and are often the sites of star formation.

Molecular clouds are usually detected because of the presence of other heavier molecules such as carbon monoxide. They form the basis of spiral structures such as arcs, arms and rings.

See also

• A list of molecular clouds.