Stars: Birth And Death (Part 2)

Gravity rules the life cycle of stars. During the Red Giant dying stage in the life of an average size star, its outer layers are blown off in vast clouds of dust and gas called "nebulae" that contain hydrogen, oxygen, and nitrogen. Gravity crushes the remaining atoms into a remnant core called a white dwarf. The gravity of giant stars-10 to 20 times larger than average-will, at the end of their life in a supernova explosion, crush together even mutually repulsive protons and electrons, leaving a remnant rotating core of neutrons (i.e., a pulsar). Also explains how stars 20 to 100 times average size collapse into a core so dense that its gravity doesn't even allow light to escape (i.e., a black hole).

(Source: DCMP)