Star Stuff
Chapter twelve addresses the idea of stars: how they are formed, their lives, and how they die. Stars form in cold, dense clouds whose pressure cannot resist the gravitational contraction. Once a large cloud of gas begins to collapse, the gravity pulls the gas toward the clouds more dense region, causing it to fragment into smaller pieces.
As we learned in Chapter 11, stars can be in a binary system which they orbit another star. The two types of stars we examined in this chapter were low mass stars and high mass stars. Low mass stars shine for 90% of their life in the main sequence. After the star has used all of its hydrogen, it will begin to expand. The core of the star will shrink as the outer shell expands, and the core shrinkage will cause the star to eventually quit burning. When it dies, the star will eject its outer layer and the core will be left as a white dwarf.
High mass stars live shorter lives because they fuse their core hydrogen into helium at a much more rapid pace. Near the end of its life, the high mass star will expand to become a supergiant, and the fusion will proceed in its core and shell. The core will eventually become too hot to fuse, and the iron will pile up, causing the star to die out.
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