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Our Galaxy

Jewel Box Cluster. Naked eye stars. Eagle Nebula. Crab Nebula. Our Galaxy. Earth = 100 n m = virus Sun = 10 μ m = cell Earth orbit = ¼ cm = pin head Solar system = 20 cm = saucer

matthewgriffin
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Our Galaxy

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  1. Jewel Box Cluster Naked eye stars Eagle Nebula Crab Nebula Our Galaxy Earth = 100 nm = virus Sun = 10 μm = cell Earth orbit = ¼ cm = pin head Solar system = 20 cm = saucer Nearest star = 250 m = lawn Solar system Galaxy Center

  2. Halo: No ionization nebulae, no blue stars  no star formation Disk: Ionization nebulae, blue stars  star formation

  3. Much of star formation in disk happens in spiral arms Ionization Nebulae Blue Stars Gas Clouds Whirlpool Galaxy

  4. 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

  5. Mass within Sun’s orbit: 1.0 x 1011MSun Total mass: ~1012MSun

  6. We can measure rotation curves of other spiral galaxies using the Doppler shift of the 21-cm line of atomic H

  7. Spiral galaxies all tend to have flat rotation curves indicating large amounts of dark matter

  8. Gravitational lensing, the bending of light rays by gravity, can also tell us a cluster’s mass

  9. 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

  10. Hubble Ultra Deep Field

  11. Hubble Ultra Deep Field Elliptical Galaxy EllipticalGalaxy Irregular Galaxies Spiral Galaxy

  12. NGC 3310 Spiral Galaxy

  13. NGC 1365 Barred Spiral Galaxy

  14. Barred Spiral Galaxy: Has a bar of stars across the bulge

  15. Elliptical Galaxy: All spheroidal component, virtually no disk component

  16. Lenticular Galaxy: Has a disk like a spiral galaxy but much less dusty gas (intermediate between spiral and elliptical)

  17. Irregular Galaxy

  18. Interacting galaxies

  19. Hubble’s galaxy classes Spheroid Dominates Disk Dominates

  20. Spiral galaxies are often found in groups of galaxies (up to a few dozen galaxies)

  21. Elliptical galaxies are much more common in huge clusters of galaxies (hundreds to thousands of galaxies)

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