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The Stars

The Stars. HNRT 227 Chapter 14 22 October 2015. Great Idea: The Sun and other stars use nuclear fusion reactions to convert mass into energy. Eventually, when a star’s nuclear fuel is depleted, the star must burn out. Chapter Outline. The Nature of Stars The Anatomy of Stars

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The Stars

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  1. The Stars HNRT 227 Chapter 14 22 October 2015 Great Idea: The Sun and other stars use nuclear fusion reactions to convert mass into energy. Eventually, when a star’s nuclear fuel is depleted, the star must burn out.

  2. Chapter Outline • The Nature of Stars • The Anatomy of Stars • The Variety of Stars • The Life Cycles of Stars

  3. The Nature of Stars

  4. The Nature of Stars • Astronomy • Oldest science (?) • Star • Ball of gas • Fusion reactor • All stars have a beginning and an ending

  5. Measuring the Stars with Telescopes and Satellites • Electromagnetic radiation • Measurement of photons • Wavelength • Intensity • Direction • Variation

  6. Telescopes

  7. Orbiting Observatories • Great Observatories Program • Hubble Space Telescope • Spitzer Infrared Telescope • Chandra X-Ray Observatory

  8. The Anatomy of Stars

  9. The Structure of the Sun • Structure • Stellar core • Radiative zone • Convection zone • Photosphere • Chromosphere • Corona • Solar Wind • Stream of particles

  10. Our Sun

  11. More On Solar Structure • Hydrogen fusion takes place in a core extending from the Sun’s center to about 0.25 solar radius • The core is surrounded by a radiative zone extending to about 0.71 solar radius • In this zone, energy travels outward through radiative diffusion • The radiative zone is surrounded by a rather opaque convective zone of gas at relatively low temperature and pressure • In this zone, energy travels outward primarily through convection

  12. How do we know the Sun’s interior? • Helioseismology is the study of how the Sun vibrates • These vibrations have been used to infer pressures, densities, chemical compositions, and rotation rates within the Sun

  13. Magnetic Fields

  14. Northern Lights (Aurora Borealis)

  15. The Sun’s Energy Source: Fusion • Sun’s Energy Source • Historical • Current • hydrogen • Fusion • 3-steps-hydrogen burning • P + P D + e+ + neutrino + energy • D + P 3He + photon + energy • 3He + 3He 4He + 2protons + photon + energy • Life expectancy • 11-12 billion years

  16. The Variety of Stars • Differences • Color • Brightness • Distance • Absolute brightness • Energy output • luminosity • Apparent brightness • Behavior • Total mass • age

  17. The Cosmic Distance Ladder • Distance • Light-years • Measurement • Triangulation (parallax) • Spectroscopic parallax • Cepheid variable • Tully-Fisher • Supernovae Type Ia • Hubble’s Law

  18. The Hertzsprung-Russel Diagram • Star Groupings • Main-sequence stars • Red giants • White dwarfs

  19. Step 1 to an H-R Diagram • Plot for the 20 nearest and brightest stars to Earth

  20. Step 2 to an H-R Diagram • Reversing the y-axis

  21. Step 3 to an H-R Diagram • Reversing the x-axis • Lowest temperature to the right

  22. A Standard H-R Diagram

  23. The Life Cycles of Stars

  24. The Birth of Stars • Nebular Hypothesis • Laplace

  25. The Main Sequence and the Death of Stars • Stars much less massive than the Sun • Glows 100 billion years • No change in size, temperature, energy output • Brown dwarfs • Some don’t consider these stars

  26. The Main Sequence and the Death of Stars • Stars about the mass of the sun • Hydrogen burning at faster rate • Move off main sequence • Helium burning • Red giant • Begin collapse • White dwarf

  27. Gas cloud Fragmentation Protostar Kelvin-Helmholz contraction Hayashi Track Ignition Adjustment to Main Sequence Hydrogen Core Depletion Hydrogen shell burning Helium flash Helium core burning Helium core depletion Helium shell burning Helium shell flashes Planetary nebula White Dwarf The Life Cycle of a Star Like the Sun

  28. Sun’s Life Cycle on H-R Diagram

  29. The Main Sequence and the Death of Stars • Very Large Stars • Successive collapses and burnings • Iron core • Catastrophic collapse • supernova

  30. H -> He He -> C C -> O Layers O -> Ne of Nuclear Ne -> Mg Fusion Mg -> Si in Si -> Fe High Mass Fe Stars Layers of Massive Star

  31. Neutron Stars and Pulsars • Neutron Star • Dense and small • High rotation rate • Little light • Pulsar • Special neutron star • Electromagnetic radiation • End state of supernova

  32. Black Holes • Black Hole • Result of collapsed large star • Nothing escapes from surface • Cannot “see” them • See impact on other stars, dust, etc. • Detect x-rays, gamma rays

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