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Galaxies in the Universe

Galaxies in the Universe. Galaxies: From Here to the Horizon.

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Galaxies in the Universe

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  1. Galaxies in the Universe

  2. Galaxies: From Here to the Horizon Thus the explorations of space end on a note of uncertainty… Eventually, we reach the dim boundary – the utmost limits of our telescopes. There we measure shadows, and we search among ghostly errors of measurement for landmarks that are scarcely more substantial. Edwin Hubble (1889 – 1953) American astronomer

  3. Types of Galaxies • Spiral Galaxies – 2 or more arms winding out from the center • Barred Spirals - have an elongated central region (or bar) • Elliptical Galaxies – No spiral structure, smooth featureless appearance, generally elliptical shape • Irregular Galaxies – No arms, nor a smooth appearance, have random patches

  4. Spirals Variations?

  5. Spirals • have a disk component and bulge & halo • disk contains gas & dust • relative sizes of bulge/disk & amount of gas/dust vary • appear white because they contain both blue & red stars

  6. Spirals • Star Types • Mix of old and new stars (pop I & pop II) • Young, blue stars in the spiral • This is cause by the high amounts of interstellar mass (ISM) clouds

  7. Spirals “Edge-on”

  8. Spiral Arms as Density “Traffic Jams” (Density waves)

  9. Barred Spirals

  10. Elliptical Galaxies • only have a spheroidal component;nodisk • very little gas/dust, little active star formation • appear red because they contain mostly red stars

  11. Elliptical Galaxy Star Types • Mostly old stars (pop II)

  12. Irregular Galaxy Variations • “none of the above”; neither spiral nor elliptical • appear white & dusty: lots of gas & dust • have more in common w/ disk component of spirals • distant galaxies more likely to be irregular • So…more common when the Universe was young

  13. Irregular Galaxy Star Types • Young blue stars are common due to high ISM • Has a large percentage of ISM left • (will last a long time – lots of “star fuel”)

  14. Discovered Cepheid variables in Andromeda galaxy. (a pulsating star’s period) Calculated distance to Andromeda galaxy. 2.2 million light years Developed a classification scheme for galaxies. Edwin Hubble(1889-1953)

  15. Hubble’s Classification System

  16. Hubble Law • Hubble observed a redshift in almost all galaxies (a few exceptions of nearby galaxies), that increased for more distant galaxies • What does this mean?? • The universe is expanding!

  17. Hubble Law • Hubble discovered that a galaxies recession velocity (speed at which they move away) increased with distance from the MW. V = HD • V = Velocity (in km/s) • H = 71 km/sec/Mpc(The Hubble Constant) • D = Distance (megaparsecs)

  18. Hubble’s Law: Velocity of Distant Galaxies Increases with Distance Farther Galaxies move away from us faster Closer Galaxies move away from us

  19. Hubble Law

  20. V = HD H = 71 km/s/Mpc Hubble Law Example • From a galaxy’s spectrum, its recession velocity is 56,000 km/s. How far away is the galaxy?

  21. V = HD H = 71 km/s/Mpc Hubble Law Example • If a distance galaxy is 1,109 Mpc away, how fast is the galaxy moving away from our galaxy? • From a galaxy’s spectrum, its recession velocity is 37,500 km/s. How far away is the galaxy?

  22. Cosmic Distance Ladder!

  23. Galactic “Cannibalism” http://viz.adrian.pw/galaxy/

  24. Evidence of Dark Matter

  25. Gravitational Lenses Suggest Dark Matter

  26. Expanding Chocolate Chip Cake

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