Giant molecular clouds GMCs

Giant molecular cloud (GMC) A region of space with a larger molecular density of 10s cm-3 and a rich chemical composition. The GMC may also contain young stellar objects. 

Three of the most interesting types of these envelopes are HI clouds, HII clouds, and giant molecular clouds (GMCs). These three regions differ in the types of molecules they contain, their temperature, and their densities. 

HI clouds and giant molecular clouds (GMCs) are much cooler than HII regions, with temperatures of no more than about 100K and 10K respectively. HI clouds consist of hydrogen atoms, and GMCs almost certainly consist of hydrogen molecules. The total mass of... 

Giant molecular clouds the GMCs have a lifetime of order 106—10s years and are the regions of new star formation. The Orion nebula (Orion molecular cloud, OMC) is some 50 ly in diameter and 1500 ly from Earth. The temperature within the cloud is of order 10 K and the atomic density is 106 cm-3. The chemical composition is diverse and contains small diatomic molecules, large polyatomic molecules and dust particles covered with a thick ice mantle. 

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