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The Life Cycle of Stars: From Birth to Death in the Cosmos

Explore the fascinating journey of stars, beginning with their birth from the interstellar medium to their transformation into hydrogen-burning stars. Delve into the stages of stellar evolution, including expansion into red giants, potential collapse into neutron stars or black holes, or the creation of white dwarfs and supernova explosions. Understand the inner workings and construction of stars, the balance of gravity and pressure, and the processes of nuclear fusion that power these celestial giants. Discover how energy flows from a star's core to its surface, forming the basis of stellar luminosity.

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The Life Cycle of Stars: From Birth to Death in the Cosmos

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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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