ASTR 1020: Chapter 21
22 Cards in this Set
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Life histories of galaxies can be determined by
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looking at galaxies at different distances
deep observations show us very distant galaxies as they were much earlier in time (old light from young galaxies)
observing at different distances show us how they age
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Galaxies formed in
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regions of slightly higher density in the early universe
gravity of denser regions pulled in surrounding matter
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Protogalactic clouds formed
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from denser regions contracting
Hydrogen & helium gas in these clouds formed the first stars
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Differences in observed galaxy types may be due to:
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spin of protogalactic cloud
density of protogalactic cloud
collisions & mergers, close encounters
starburst phenomenon
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What are conditions in protogalactic cloud?
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spin & density
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Spin of protogalactic cloud
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the initial angular momentum of the protogalactic cloud could determine the size of the resulting disk
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Density of protogalactic cloud
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elliptical galaxies could come from dense protogalactic clouds that were able to cool & form stars before gas settled into a disk
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Collisions
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more likely early in time b/c galaxies were closer together
collisions nearby trigger bursts of star formation
can transform 2 spiral galaxies into elliptical
may explain why elliptical galaxies tend to be found where galaxies are closer together
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Mergers/Close encounters
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giant elliptical galaxies at the centers of clusters seem to have consumed a number of smaller galaxies
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Starburst galaxies
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transforming its gas into stars much more rapidly than normal galaxy
are forming stars so quickly that they would use up all their gas in less than a billion years
intensity of supernova explosions in starburst galaxies can drive galactic winds
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Active galactic nucleus
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if the center of a galaxy is unusually bright it is an active galactic nucleus
galaxies typically emitting light from the core that is not coming from the stars
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Major characteristics of active galactic nucleus
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very luminous
most light is not coming from stars
variable light output (luminosities can rapidly vary)
explosive events such as jets (near light speed)
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Types of active galactic nucleus
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quasars,
radio galaxies
Seyfert galaxies,
BL Lac objects
N galaxies
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Different types of objects arise because
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of different perspectives as seen from Earth & differing ages of the host galaxies
We're really seeing the same type of thing over and over
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Different types of galaxies also indicates that...
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the universe is evolving since this phenomenon tends to occur in distant/younger objects
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Quasars
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are the most luminous examples of active galactic nucleus
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What can you conclude from the fact that quasars usually have very large redshift?
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they are generally very distant
they were more common early in time
galaxy collisions might turn them on
nearby galaxies might hold dead quasars
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Radio galaxies
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contain active nuclei shooting out vast jets of plasma that emits radio waves coming from electron that move at near light speed
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Power source for active galactic nucleus
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Power source for active galactic nucleus
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The mass of a galaxy's central black hole is related to...
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the mass of its bulge
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Evidence of active galatic nuclei
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rotation speeds of gas in nearby active galactic nucleus
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Distant quasars can be used as probes of...
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of distant objects lying between the quasar and us.
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ASTR 1020: STUDY GUIDE