Massive stars and low-mass stars live different lives.  They are born in different environments, fuse different elements during the course of their lives, release different amounts of radiation across the electromagnetic spectrum, die in different ways, and enrich interstellar space with different metals.  We see stars at all stages of life in the galaxy, and their study allows us to piece together how stars form, and how the rarest ones are different. The image above shows two distinct clouds, both about 5,000 light years away in the constellation Cygnus, along the Galactic plane.  The smaller bubble on the left, literally...