Astro Exam 4

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  1. New Distance estimate methods
    • Identify (and calibrate) objects that could serve as "standard candles" 
    • -Make some measure of an object which identifies its luminosity
    • -Use this luminosity and measure apparent brightness to infer distance to it
  2. Standard Candle- Main sequence fitting
    • Distance Estimate 1
    • Start with a cluster with known distance (through paralax) 
    • Compare with other cluster
    • Get the distance of the other cluster from the difference in brightness
  3. Chepheid Variable stars
    • Distance estimate 2
    • Period luminosity relation
    • Brighter cepheids have longer periods
  4. White dwarf supernovae
    • Distance estimate 4
    • Nearly the same amount of energy released every time
    • "Standard Explosion" fusion of 1.4 solar masses of material
    • Bright enough to be seen halfway across the universe (used for mapping large distances)
  5. Distance ladder to measure the universe
    • Radar
    • Parallax
    • Main sequence fitting
    • Cepheids
    • Distant Standards
  6. Edwin Hubble
    in 1924 identified cepheids in Andromeda (M32) -> showed they were far outside the Milky Way
  7. Hubbles Law
    • v = H x d
    • Velocityof of reccession = hubbles constant times distance
  8. How we know galaxy evolution
    • Observe galazies at different redshifts
    • This assembles a sequence of galaxies showing birth and evolution
    • Check via computer models of gas, gravity and star formation
  9. How did galaxies form
    • Matter originally filled all of space almost uniformly
    • Gravity of denser regions pulled in surrounding matter
  10. Starbursts
    • Galaxies that form stars so quickly that they would use up all their gas in less then a billion years
    • Can have up to 100X more star formation then ours
  11. Quasars and active galactic nuclei
    • Galaxies with strange stuff going on in their centers
    • Galaxies at high redshift have extremely active centers
    • We know they are tiny because of their change in brightness is within a few light hours
    • Quasars can show materials in the universe through emission lines
  12. Characteristics of Active Galaxies
    • Luminosity can be enormous (>10^12 Lsun)
    • Luminosity can rapidly vary (comes from a space smaller than solar system)
    • Emit energy over a wide range of wavelengths (contain matter with wide temperature range)
  13. Quasar Central Engines
    • They are powered by accretion disks around supermassive black holes
    • In some quasars, huge jets of material are shot out at the poles. These jets are strong radio sources
  14. Do all galaxies have supermassive black holes?
    • Probably yes
    • Part of normal galaxy formation?
    • More quasars seen in distance universe than now
    • Black holes gradually grow, but can run out of available fuel and become nearly invisible (like in our milky way)
  15. Dark matter
    an undetected form of mass that emits little or no light but whose existance we infer from its gravitational influence
  16. Dark energy
    An unknown form of eergy that seems to be the source of a repulsive force causing the expansion of the universe to accelerate
  17. Contents of Universe
    • 4.4% normal matter
    • - .6% in stars
    • - 3.8% outside stars
    • 23% dark matter
    • 73% dark energy
  18. Weighing a galaxy
    • A total mass within an orbit can be found by measuring the orbital velocity
    • M = R v^2 / G
  19. Rotation curves
    • Motions of stars in the galaxy
    • Reveal that dark matter extends beyond visible part of the galaxy, mass in 10x stars and gas
  20. Galaxy clusters reveal dark matter in three ways
    • #1 galaxy velocities too large to be explained by gravity of visible galaxies
    • #2 Hot x-ray emitting gas in cluster
    • #3 gravitational lenses
    • all have the same dark to normal matter ratio
  21. Gravitational lensing
    • Light is bent by gravity
    • The greater the mass the greater the gravity bend
  22. WIMPS
    • Weakly interacting massive particles
    • Non baryonic matter = subatomic particles
  23. Both our past and our future depend on dark matter
    • Past: birth of galaxies and clusters
    • - dark matter provided the first tugs to assemble galaxies and clusters out of protogalactic clouds
    • -Without dark matter there would be no massive structure
    • Future: fate of the universe
    • - is there enough dark matter in the universe to reverse the expansion and pull the universe back together again
  24. Ages of the universe for the different models
    • recollapsing - 4.4 bil
    • critical - 9 bil
    • coasting - 13 bil
    • accelerating 14 bil
  25. How can universe be accelerating
    "dark energy" outweighs every other form of mass/ energy
  26. What were conditions like in early universe?
    The early universe must have been extremely hot and dense
  27. Four known forces in the univserse
    • Gravity
    • Electromagnetism
    • Strong force
    • Weak force
  28. Cosmic microwave background
    • Penzias & Wilson in 1965 discoverd cosmic microwave background radiation (CMB)
    • -photons created when hot universe was only 380,000 years old -as first atoms formed
    • Very uniform radiation but not completely (1 part in 100,000)
  29. Chemical abundances
    • Big bang theory prediction:7-1 proton to neutron ratio, because protons are lighter
    • -should lead to 75% H, 25% He (by mass)
    • Matches observations of nearly primordial gas
  30. Expansion of the universe
    Hubbles expansion show that all galaxies are moving away from us
  31. Inflation
    • Solves 3 problems left unanswered
    • -Why is the universe so uniform
    • -Where did structure come from
    • -Why is the density of the universe so close to the critical density
  32. Fundamental answers about the universe from late 80s to now
    • What is the age of the universe?
    • Would the expansion of the universe stop? unknown in 80s
    • What can the CMB radiation tell us? unknown in 80s 
    • Do black holes exist? unknown in 80s
    • Do other stars have planets? unknown in 80s
    • How did the structure in the universe formed?
    • What is the nature of the mysterious gamma ray bursts? unknown in 80s
    • How do stars form? unknown in 80s
    • Are there other life forms in the universe? unknown in 80s
    • What is the makeup of the universe? unknown in 80s
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Astro Exam 4
2014-05-05 00:53:33

Astro exam 4
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