astro chapter 20

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  1. Where does a stars helium content increase the fastest
    in it's core where the temperatures are highest and the burning is fastest
  2. hydrogen-shell burning stage
    • core is full of helium and not hot enough to fuse, contracts due to lack of energy balance
    • shell around core heats up, higher temp than found in core, star burns helium in shell much faster and continues to increase as helium shell contracts
    • star gets brighter, more energy produced once fusion in the core stops
  3. how long does it take a normal main-sequence star to become an elderly red giant
    100 million years
  4. what goes on with start temperature between stages 8-9
    • stage 8, surface temperature has fallen to the point at which much of the interior is opaque to the radiation from within. Convections carries the cores energy to the surface
    • temperature remains nearly constant between these stages
  5. stage 9 - radius and luminosity
    • luminosity man hundred times solar value
    • radius is 100 times larger
  6. red giants core density (stage 9)
    • 10^8 kg/m^3
    • contrast with 10^-3 in the giants most outer layer 5000 average density for earth and 150,000 in the present core of the sun
    • about 25% of the mass of the entire star is packed into its planet sized core
  7. what are Helium-4 nuclei traditionally know as
    alpha particles
  8. stage 10 laws
    governed by the laws of quantum mechanics
  9. pauli exclusion prinicple
    prohibits the electrons in the core from being squeezed together - electron degeneracy ensues.
  10. Helium flash energy
    • results in reduction of energy output
    • surface temperature gets high, luminosity gets lower
  11. stage 9-10 transition time (helium flash)
    100,000 years, quick
  12. asymptotic-giant branch
    • the second ascent of the star into the giant branch.
    • Follows life after the horizontal branch
  13. black dwarfs are about what size
    size of earth
  14. sirius b
    a white dwarf in orions dog
  15. what stage is the main sequence
    stage 7
  16. brown dwarfs
    the end product of low-mass protostars unable even to fuse hydrogen in their cores
  17. why are stellar clusters good tests sites for the theory of stellar evolution
    they formed at the same time, from the same interstellar cloud, and with virtually the same composition
  18. turnoff
    astronomers refer to the high-luminosity end of the observed main sequence as the main sequence turnoff.
  19. turnoff mass
    the mass of star that is just evolving off the main sequence at any moment is known as the turnoff mass
  20. when did all of the globular clusters in our galaxy form
    10-12 billion years ago
  21. roche lobe of two stars
    • the roche lobes of two stars meet at a point on the line joining them - the inner lagrangian point - gravitational pulls of the two stars exactly balance each other
    • if a star expands past it's roche lobe a period of rapid mass transfer ensues
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astro chapter 20
2014-04-21 23:19:30

astro chapter 20
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