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Lecture 34 – Galaxies and the Universe

Lecture 34 – Galaxies and the Universe. Repeatedly said there are other galaxies. Now details Large Magellanic Cloud (satellite to Milky Way) . Distance=50 kpc. Pic: http://antwrp.gsfc.nasa.gov/apod/ap010804.html M31: Distance=730 kpc, Pic: http://antwrp.gsfc.nasa.gov/apod/ap021021.html

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Lecture 34 – Galaxies and the Universe

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  1. Lecture 34 – Galaxies and the Universe • Repeatedly said there are other galaxies. Now details • Large Magellanic Cloud (satellite to Milky Way) . Distance=50 kpc. Pic:http://antwrp.gsfc.nasa.gov/apod/ap010804.html • M31: Distance=730 kpc, Pic:http://antwrp.gsfc.nasa.gov/apod/ap021021.html • M33: Distance = 670 kpc, Pic: http://antwrp.gsfc.nasa.gov/apod/ap030924.html

  2. These are the closest galaxies Question: How do we know their distances?

  3. Our Galactic Neighborhood- The Local Group Galaxies come in clusters, too A new unit, the Megaparsec

  4. Beyond the Local Group • Other small groups of galaxies • Typical spacing of a few Megaparsecs • Our “neighbors” include some of the brightest binocular galaxies • See Appendix 15 for list

  5. Types of Galaxies Spirals, Ellipticals, Irregulars

  6. The Larger Neighborhood

  7. The Virgo Cluster • Distance ~ 20 Megaparsecs • > 1000 galaxies • Largest are giant ellipticals like M87

  8. Not the end of the story: the Abell clusters • Published in 1958 • 2718 “Rich Clusters” like the Virgo cluster • Most distant 2 billion light years

  9. The Abell Clusters

  10. Now the question: how can you know the distances to these objects? You can’t see Cepheids that far out

  11. Turn to one of Hubble’s greatest discoveries • He discovered galaxies as “island universes” • Measured distances to galaxies • Measured velocities (toward us or away) • How?

  12. Illustration of a galactic redshift

  13. The Hubble Relation for Galaxies • Galaxies in all directions receding from us • The more distant they are, the faster they are receding • v=H0d • v = speed of recession (km/sec), d= distance (Mpc), H0 “Hubble Constant”, (km/sec/Mpc), H0 = 70 km/sec/Mpc

  14. The Hubble Relation for Galaxies If you measure the redshift, you know the distance

  15. With measurements of distances, you can map out the distribution of galaxies

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