Astro Exam 2

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Astro Exam 2
2014-04-02 11:40:27

Astro exam 2
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  1. Hydrogen fusion by the proton-proton chain
    • Describes fusion process in the sun
    • -Two protons fuse to make deuterium nucleus (occurs twice)
    • -Then a proton fuses with this to make hlium 3 (twice) 
    • -Then the two helium 3's fuse to form helium 4 realeasing two protons
    • - Result is gamma rays
  2. Neutrinos
    • -made by hydrogen fusion in core
    • -have very small masses
    • -don't interact with anything
  3. Hydrostatic equilibrium "gravitational equilibrium"
    • -Pull of gravity = pull of pressure
    • -Spherical nature of gravity makes it round
    • -High pressure needed at the center
  4. The solar thermostate
    • -If suns temperature rose fusion rate would rise causing pressure to expand the core and cool it bringing it back to equilibrium
    • -If suns temperature dropped fusion would slow and pressure would be low causing the core to contract and heat up bringing the sun back to equilibrium
  5. How do we know what the inside of the sun looks like
    • Neutrinos - they validate our hypothesis, direct product of fusion
    • Mathematical models - know how how big it is, knowing the surface temp. knowing the mass
    • Helioseismology - Sun earth quakes, the sun vibrates around, depending on how the sun is vibrating we can measure how certain parts of thesun are moving towards or away from us
  6. When prominences go bad
    • -prominences are gases released by two sunspots resulting in an arch trapped in these loops
    • -When magnetic fields lines in a prominence snap energy and light is released in the form of flare
    • -Charged particles are spewed out into space through coronal mass ejections
  7. Inverse square law of brightness
    • Apparent brightness = luminosity / distance ^2
    • -Apparent brightness - how bright it appears to us here on earth 
    • -Luminosity - energy emitted (Joules/sec or watts
  8. Astronomer's toolbox: Distance, Luminosity, Temperature, Mass
    • Distance - parallax good to nearby stars but not beyond
    • Luminosity - measure apparent brightness and distance, infer luminosity
    • Temperature - spectral classification
    • Mass - for binary orbits, get orbital parameters we can figure out mass
  9. The Hertzsprung Russel Diagram
    Depicts: temperature, color, spectral class, luminosity, radius and mass
  10. Main sequence stars
    • -burning hydrogen in their cores
    • -Temps hotter for more massive stars
    • -More luminous
  11. Protostar to main sequence
    • Protostar looks star like after surrounding gas is blown away, thermal energy comes from gravitational contraction not fusion
    • Contraction continues until core is hot enough for nuclear fusion
    • Contraction stops when internal energy equals surface energy
  12. Thermal vs. degeneracy pressure
    • Thermal: depends on heat content, main form of pressure in most stars, (think expanding balloon)
    • Degeneracy pressure: particles can't be in the same state in the same place, not dependent on heat content
  13. Life track
    • -Protostar assembles from collapsing sloud
    • -shrinks and heats as gravitational energy is converted into thermal energy
    • -temperature rises as radiation becomes main form of energy flow
    • -fusion rate increases until there is a balance of energy on the star
  14. Limits of main sequence stars
    • -stars more massive than 100Msun would blow apart
    • -stars less massive than 0.08Msun can't sustain fusion
  15. Role of mass
    • determines entire life story - determines core temp
    • high mass - have shorter lives, make iron, end in supernovae explosions
    • low mass - have long live, never fuse carbon and end as white dwarfs 
    • intermediate mass - can make elements heavier than carbon but end as white dwarfs
  16. Supernova
    • Energy released by collapse of core drives out outer layers into space
    • produces most elements heavier than iron within a sec
  17. Stellar graveyard: Low mass stars, High mass stars, and even more massive stars
    • Low mass -> white dwarfs, gravity v. electron degeneracy
    • High mass -> neutron stars, gravity v. neutron generacy
    • Even more massive stars -> black holes, gravity wins
  18. White dwarf supernovae
    • If enough mass is accreted, electron degeneracy is overcome (limit is 1.4 solar masses (chandrasekhar limit))
    • Star then collapses carbon fusion begins explosively dwarf is gone
  19. White dwarf SN vs. Massive star SN
    • White dwarf SN - binary systems only, occurs in older star populations, nothing left inside
    • Massive star SN - found in young star formation regions, make neutron stars or black holes
  20. Neutron stars
    • Structure is determined by gravity vs. neutron degeneracy pressure
    • About 10 km and 1 -3 M sun
    • Made of degenerate neutrons
    • Crushing gravity
  21. Warping of space by gravity
    • gravity imposes curature on space, light's path through space will be "bent by gravity, 
    • As matter approaches event horizon, tidal forces are tremendous, object will be spaghettified
  22. Warping of time by gravity
    • -launched to a black hole time slows down as it approached event horizon
    • from mothership the probe takes forever to reach event horizon
    • light from probe is redshifted until you can't see it even in radio
    • From probes view: it heads straight into blackhole, light from mother ship is blue shifted
  23. Shapley's global clusters
    • Harlow measured distances to globular clusters
    • -appeared to be centered on a location tens of thousands of light-years from the sun
    • conclusion: sun not in center, about 2/3 out
  24. Galaxies: ultimate recyling planets
    Atomic hydrogen clouds -> molecular clouds -> star formation -> stellar lives, neclear fusion, heavy element formation -> returning gas through supernovae and stellar winds ->hot bubbles