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Typical galaxy. [A] 100 billion stars, like city – people born & die Measure rate of star birth – ~1 per year. only 14 billion stars ?? : LESS than known number We INFER that the rate of star birth was GREATER in the past. [B] Also : stars dying pollution/enrichment by elements. gradual buildup of elements ---- expect oldest stars to have few elements Next few slides show this : (NEXT SLIDE)
![Typical galaxy. [A] 100 billion stars, like city – people born & die. Measure rate of star birth – ~1 per year.](http://slideplayer.com./slide/12740127/77/images/1/Typical+galaxy.+%5BA%5D+100+billion+stars%2C+like+city+%E2%80%93+people+born+%26+die.+Measure+rate+of+star+birth+%E2%80%93+%7E1+per+year..jpg " only 14 billion stars : LESS than known number. We INFER that the rate of star birth was GREATER in the past. [B] Also : stars dying pollution/enrichment by elements. gradual buildup of elements ---- expect oldest stars to have few elements. Next few slides show this : (NEXT SLIDE)")
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Our Galaxy Earth = 100 nm = virus Sun = 10 μm = cell
Earth orbit = ¼ cm = pin head Solar system = cm = saucer Nearest star = m = lawn Jewel Box Cluster Naked eye stars Eagle Nebula Crab Nebula Solar system Galaxy Center
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Halo: No ionization nebulae, no blue stars
no star formation Disk: Ionization nebulae, blue stars star formation
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Much of star formation in disk happens in spiral arms
Ionization Nebulae Blue Stars Gas Clouds Whirlpool Galaxy
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Spiral arms are waves of star formation
Gas clouds get squeezed as they move into spiral arms Squeezing of clouds triggers star formation Young stars flow out of spiral arms
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Mass within Sun’s orbit:
1.0 x 1011 MSun Total mass: ~1012 MSun
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We can measure rotation curves of other spiral galaxies using the Doppler shift of the 21-cm line of atomic H
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Spiral galaxies all tend to have flat rotation curves indicating large amounts of dark matter
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Gravitational lensing, the bending of light rays by gravity, can also tell us a cluster’s mass
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Our Options Dark matter really exists, and we are observing the effects of its gravitational attraction Something is wrong with our understanding of gravity, causing us to mistakenly infer the existence of dark matter
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Hubble Ultra Deep Field
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Hubble Ultra Deep Field
Elliptical Galaxy Elliptical Galaxy Irregular Galaxies Spiral Galaxy
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NGC 3310 Spiral Galaxy
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NGC 1365 Barred Spiral Galaxy
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Barred Spiral Galaxy: Has a bar of stars across the bulge
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Elliptical Galaxy: All spheroidal component, virtually no disk component
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Lenticular Galaxy: Has a disk like a spiral galaxy but much less dusty gas (intermediate between spiral and elliptical)
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Irregular Galaxy
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Interacting galaxies
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Hubble’s galaxy classes
Spheroid Dominates Disk Dominates
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Spiral galaxies are often found in groups of galaxies
(up to a few dozen galaxies)
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Elliptical galaxies are much more common in huge clusters of galaxies
(hundreds to thousands of galaxies)
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