giant molecular clouds

giant molecular clouds

(GMCs) Huge molecular clouds that are the main sites for star formation in our Galaxy and others. The average linear dimension of a GMC is about 40 parsecs, total mass about 5 × 105 solar masses, with gas temperatures of 15–30 K. GMCs are found to lie mostly in the Galactic plane. Warmer active clouds lie in the spiral arms; smaller cooler clouds are distributed almost randomly throughout the disk. It is estimated that there are between 4000 and 5000 GMCs in the Galaxy, implying a total mass of 2 × 109 solar masses. This represents a large proportion – possibly up to 50% – of the Galaxy's gas content, and is of importance in theories of galactic evolution and structure.