PHYS 102 Chapter Notes - Chapter 33: Stellar Evolution, Parsec, Cosmological Principle
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PHYS 102 Full Course Notes
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The night sky contains myriads of stars including those in the milky way, which is a (cid:862)side view(cid:863) of our galaxy looking along the plane of the disc. Beyond our galaxy are billions of other galaxies. Stellar evolution: the birth and death of stars. Stars are believed to begin life as collapsing masses of hydrogen gas (protostars). As they contract, they heat up (potential energy is transformed to kinetic energy). When the temperature reaches about 10 million degrees, nuclear fusion begins and forms heavier elements (nucleosynthesis), mainly helium at first. The energy released during these reactions heats the gas so its outward pressure balances the inward gravitational force, and the young star stabilizes as a main-sequence star. The tremendous luminosity of stars comes from the energy released during these thermonuclear reactions. Astronomical distances are measured in light-years (1 ly = (cid:883)(cid:882)13 km). The nearest star is about 4 about 100,000 ly.
