ASTRON 1101 Lecture Notes - Lecture 18: Photosphere, Cno Cycle, Fusion Power
8 Oct 2016
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Document Summary
The sun is a massive ball of gas. To stay in hydrostatic equilibrium, it must have a very high pressure at its center. All main sequence stars generate energy by the fusion of hydrogen (h) into helium (he) in their cores. Stellar cores are hot, so the hydrogen is ionized: h = hydrogen atom, p = free proton, e- = free electron. Stellar cores are hot, so the free protons are fast. There are two pathways by which hydrogen can be fused into helium in a main sequence star. The proton-proton chain dominates at lower temperatures. The cno cycle dominates at higher temperatures. It involves carbon (c), nitrogen (n), and oxygen (o) Proton-proton chain: the dominant energy source in the sun (98. 3% of the sun"s fusion energy is from the proton-proton chain) The p-p chain produces: neutrinos gamma-ray photons positrons (which annihilate with electrons to make more photons) Cno cycle: the dominant energy source is massive main sequence stars.
