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Galaxies

Galaxies. 1925 - Edwin Hubble uses Cepheid Variables in M31 to measure a distance of 900,000 LY from us. Typical Cepheid Variable Light curve. 1925 - Edwin Hubble uses Cepheid Variables in M31 to measure a distance of 900,000 LY from us. (actually it is 2,200,000 LY).

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Galaxies

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  1. Galaxies

  2. 1925 - Edwin Hubble uses Cepheid Variables in M31 to measure a distance of 900,000 LY from us.

  3. Typical Cepheid Variable Light curve

  4. 1925 - Edwin Hubble uses Cepheid Variables in M31 to measure a distance of 900,000 LY from us. (actually it is 2,200,000 LY)

  5. 1925 - Edwin Hubble uses Cepheid Variables in M31 to measure a distance of 900,000 LY from us. (actually it is 2,200,000 LY) - Galaxies are of different types: 1. Spirals 2. Ellipticals 3. Irregulars

  6. Spirals: - spiral arm structure in a Disk - dust present in Disk - on-going star formation (young & old stars present) - may contain a Bar in the Central Bulge Ellipticals: - no spiral arm structure, no disk - little, if any, dust - old stars - can be very large, or very small

  7. Irregulars: - no regular structure - very large amounts of dust and gas - lots of star formation (many hot, massive, young stars) - usually small

  8. Classifying Galaxies • For Spiral Galaxies: • - can have a large Bulge and tightly wound Spiral Arms -> Sa • intermediate Bulge size and winding of Spiral Arms -> Sb • - can have a small Bulge and loosely wound Spiral Arms -> Sc • - if there is a Bar: SBa, SBb, SBc • For Elliptical Galaxies: • - Spherical shape -> E0 • : • : • - very flattened, disk-like -> E7

  9. The Hubble Tuning Fork Diagram Note: S0 = Disk, but no spiral arms, some dust

  10. M31

  11. M63

  12. M77

  13. M91

  14. M83

  15. M32

  16. M110

  17. NGC 5866

  18. NGC 2784

  19. M82

  20. Large Magellanic Cloud

  21. The Hubble Law - in 1929 Hubble found that there was a correlation between galaxies’ distances and the redshifts in their spectra

  22. NGC 2775

  23. NGC 2903

  24. Hubble’s original diagram

  25. v, in km/sec d, in parsecs Slope of line = v/d = Ho, the Hubble Constant -> d = v/Ho

  26. - best current value for Ho is: 23 km/sec/ MLY or 72 km/sec/ Mpc

  27. - Implications of the Hubble Law: 1. The Universe is expanding 2. The Universe had a definite beginning (the Universe is not infinitely old) 3. Can use the Hubble Law to find distances to Galaxies

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