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Birth out of the interstellar medium

Birth out of the interstellar medium. Contraction to a normal hydrogen-burning star. Expansion to red giant. Collapse to neutron star OR black hole. Contraction to white dwarf OR . . . . . . supernova explosion. Stellar Insides. Stellar Insides: How are stars constructed?.

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Birth out of the interstellar medium

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  1. Birth out of the interstellar medium Contraction to a normal hydrogen-burning star Expansion to red giant Collapse to neutron star OR black hole Contraction to white dwarf OR . . . . . .supernova explosion

  2. Stellar Insides

  3. Stellar Insides: How are stars constructed? Atmosphere Core Envelope

  4. A few principles . . . • Stars tend to remain • stably inflated, more or • less. Gravity balances pressure: Hydrostatic Equilibrium

  5. Center of Sun: 3 billion atmospheres

  6. Stars must be hotter • on the inside. Center of Sun: 16 million K High temp, pressure  gas completely ionized: Plasma

  7. Thermonuclear Fusion • Stars require a powerful, • stable energy source. Two particles collide & fuse – form heavier particle.

  8. Net reaction in main sequence stars: 4 protons (hydrogens)  helium + neutrinos + energy Proton-proton (PP) chain 2 1H + 1H  2H + positron + gamma ray + neutrino 1H + 2H  3He + gamma ray 3He + 3He  4He + 1H + 1H 2 2H  Deuterium

  9. Alternative: CNO Cycle

  10. * Energy comes from conversion of mass into energy: mass (41H)  mass(4He)  m (> 0) E = mc2 gamma rays, neutrinos, positrons + energy of motion * Fusion requires high temp & density: collisions must be frequent & violent

  11. Nucleosynthesis * Important consequence: creation of elements that did not previously exist!

  12. Sun’s luminosity = 3.9  1026 Watt  Sun converts 4 million tons hydrogen to energy per second! Stars lose mass over time!

  13. Net heat flow Transporting energy from core to surface 1. Via photons (radiative transfer): ‘random walk”

  14. 2. Via convection Hot gas rises . . . cool gas sinks.

  15. Convective zone Radiative zone Sun

  16. Solar granules

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