AST201H1 Chapter Notes - Chapter 17.3: Degenerate Matter, Cno Cycle, Strong Gravity
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AST201H1 Full Course Notes
Only high-mass stars produce the full array of elements on which life depends. The cores of low-mass stars never become hot enough to fuse elements heavier than helium: heavier nuclei contain more positively charged protons and therefore repel each other more strongly than lighter nuclei (thus require high temperatures). High-mass stars fuse increasingly heavy elements until all possible fusion sources are exhausted: when fusion stops for good, gravity causes the core to implode suddenly, which then causes the sun to self-destruct in a supernova. All stars are formed out of a cloud fragment that gravity forces to contract into a protostar: hydrogen fusion begins when the gravitational potential energy released by the contracting protostar makes the core hot enough. Low-mass stars fuse hydrogen into helium through the proton-proton chain. The cno act as catalysts for hydrogen fusion, making it proceed at faster rates than would be possible by the proton-proton chain alone.