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The Stars

Learn about the nature of stars, their structure, variety, and life cycles. Discover how stars are measured, the energy source of the Sun, and the stages of a star's life.

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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. iClicker Question • How often do you look up at the night time sky? • A Always (when possible) • B Often • C Sometimes • D Never

  4. iClicker Question • Do you enjoy looking at the stars? • A yes • B no

  5. The Nature of Stars

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

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

  8. Telescopes

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

  10. iClicker Question • What source of data is used to analyze stars? • A chemical testing of actual samples of stellar matter • B electromagnetic radiation • C spacecraft in orbit around distant stars • D both B and C above • E no data is used

  11. iClicker Question • Telescopes are devices that: • A focus and concentrate radiation • B magnify only visible light • C all use mirrors • D both B and C above

  12. The Anatomy of Stars

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

  14. Our Sun

  15. 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

  16. 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

  17. Magnetic Fields

  18. Northern Lights (Aurora Borealis)

  19. 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

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

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

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

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

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

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

  26. A Standard H-R Diagram

  27. iClicker Question • Compared with other stars, our Sun is: • A an unusually large star • B not a star at all • C a rather ordinary star

  28. iClicker Question • The outer part of the Sun, the part that actually emits most of the light we see, is called the: • A chromosphere • B convective zone • C photosphere • D core • E radiative zone

  29. iClicker Question • The solar wind is composed of: • A bits of neutral gas • B all kinds of organic substances • C air • D charged particles including hydrogen and helium ions

  30. iClicker Question • Northern lights result from interactions of: • A the Sun’s magnetic field with Earth’s gravity • B UV light from the Sun with Earth’s ozone layer • C the solar wind with the Earth’s magnetic field

  31. iClicker Question • The Sun’s peak output of energy is in: • A the ultraviolet portion of the electromagnetic spectrum • B the visible portion of the electromagnetic spectrum • C the infrared portion of the electromagnetic spectrum

  32. iClicker Question • What is the Sun’s energy source? • A combustion of hydrogen rich chemical fuels • B fusion of hydrogen • C fission of hydrogen • D radioactive decay • E gravitational collapse

  33. The Life Cycles of Stars

  34. The Birth of Stars • Nebular Hypothesis • Laplace

  35. 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

  36. 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

  37. 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

  38. Sun’s Life Cycle on H-R Diagram

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

  40. 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

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

  42. 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

  43. iClicker Question • It is estimated that the total lifetime of our Sun is 12 billion years. Roughly, how far is it through its hydrogen-burning phase now? • A 10% • B 25% • C 50% • D 90%

  44. iClicker Question • Triangulation and Cepheid variables are methods to measure: • A distances to stars • B energy output of stars • C lifetime of stars • D composition of stars

  45. iClicker Question • A Hertzsprung-Russell diagram plots a star’s temperature versus its: • A color • B distance • C age • D size • E energy output

  46. iClicker Question • Large dust and gas clouds are commonly found throughout space. They are called: • A red giants • B galaxies • C nebulae • D supernovae • E white dwarfs

  47. iClicker Question • The fusion process in very large stars produces chemical elements up to: • A He • B C • C Fe • D U • E Pb

  48. iClicker Question • All natural elements beyond iron are created in: • A supernova explosions • B fusion of very large stars • C the big bang

  49. iClicker Question • An object that is so dense and massive that nothing, including light can escape from its surface is called: • A a supernova • B a red giant • C a white dwarf • D a black hole • E a neutron star

  50. iClicker Question • Are you surprised that the chemical elements about you were made in a supernova? • A Yes • B No

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