Parts of the Galaxy

Almost all of the galaxy's star formation regions are in the thin disk. Star formation propagates around the disk in spiral waves. The brightly lit star formation regions appear as spiral arms radiating from the central bulge.

Most thin disk stars formed in open cluster groups that condensed out together from dust and gas cloud fragments.

Much of the dust and gas in the thin disk was created by previous generations of stars that ended their lives as supernovae. The interstellar material in the thin disk therefore contains relatively high proportions of heavier "metallic" elements.