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Ch. 30 Sec. 2

Ch. 30 Sec. 2. Other Galaxies in the Universe. Finding galaxies with different shapes reveals the past, present, and future of the universe. Review Vocabulary. elliptical: relating to or shaped like an ellipse or oval. I. Discovering Other Galaxies. Edwin Hubble – 1924 Andromeda galaxy.

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Ch. 30 Sec. 2

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  1. Ch. 30 Sec. 2 Other Galaxies in the Universe

  2. Finding galaxies with different shapes reveals the past, present, and future of the universe. Review Vocabulary elliptical: relating to or shaped like an ellipse or oval

  3. I. Discovering Other Galaxies • Edwin Hubble – 1924 • Andromeda galaxy

  4. Fig. 30.10 pg.869

  5. A. Properties of galaxies • Masses of galaxies • a. Dwarf ellipticals - 1 million solar masses • b. Large spirals - 100 billion solar masses • c. Giant ellipticals - 1 trillion solar masses Leo I

  6. 2. Luminosities a. Wide range b. Smallest - dwarf spheroidals c. Supergiant elliptical galaxies (>100 times more luminous than the Milky Way) Persius

  7. 3. Dark matter a. Subatomic particle b. Interacts weakly with other matter

  8. B. Classification of galaxies • Disk-like galaxies • a. Subdivisions • i. Normal spirals - S • ii. Barred spirals - SB • b. Further subdivisions • i. Tightly wound arms - a • ii. Loosely wound arms - c Fig. 30.11 pg. 870

  9. 2. Elliptical galaxies a. Not flattened into disks b. No spiral arms c. Subdivisions i. Ratio of their major and minor axes ii. 0 - 7

  10. The Hubble tuning-fork diagram summarizes Hubble classification for normal galaxies. Fig. 30.12 pg. 870

  11. 3. Irregular galaxies (Irr)

  12. Section 30.2 Visualizing the Local Group All of the stars visible in the night sky belong to a single galaxy, the Milky Way. Just as stars compose galaxies, galaxies are gravitationally drawn into galactic groups, or clusters. The 30 galaxies closest to Earth are members of the Local Group of galaxies.

  13. II. Groups and Clusters of Galaxies A. Local Group • Diameter 2 million ly • 40 known member galaxies • a. Milky Way and Andromeda galaxies are the largest • b. Most are dwarf ellipticals

  14. Galaxy clusters larger than the Local Group might have hundreds or thousands of members and diameters in the range of about 5 to 30 million ly.

  15. B. Large clusters Most of the galaxies in the inner region of a large cluster are ellipticals. There is a more even mix of ellipticals and spirals in the outer portions. In large clusters, gravitational interactions often cause galaxies to collide. They form strangely shaped galaxies, or they form galaxies with more than one nucleus, such as the Andromeda galaxy.

  16. C. Masses of clusters • Evidence of dark matter • Clusters of galaxies are organized into even larger groups called superclusters.

  17. Measure for Measure 23

  18. III. The Expanding Universe A. 1929 - Edwin Hubble measured redshift

  19. A. Implications of redshift • All points are moving away from all other points • Greater distances increases the rate of motion • Change in size – evidence of Big Bang

  20. B. Hubble’s law Hubble determined that the universe is expanding by making a graph comparing a galaxy’s distance to the speed at which it is moving.

  21. Measuring H • a. v=Hd • v = velocity galaxy is moving away • H = Hubble constant • d = distance to galaxy measred • b. Hubble’s graph resulted in a straight line with a slope called the Hubble constant

  22. 2. Once the value of H is known, it can be used to find distances to faraway galaxies.

  23. IV. Active Galaxies • Emit large amounts of energy • Active Galactic Nuclei (AGN) Active Galactic Nuclei (AGN) are extraordinarily energetic cores of galaxies powered by supermassive black holes. AGN such as quasars, blazars, and Seyfert galaxies are among the most luminous objects in our Universe, often pouring out the energy of billions of stars. Until recently many AGN have been a mystery because they have been invisible. www.dailygalaxy.com

  24. Radio galaxies • 1. Very bright • 2. Giant, elliptical galaxies • 3. Emit more radio wavelengths than visible light • 4. Jets of ionized gas from lobes

  25. B. Quasars - starlike, very bright, extremely distant objects with emission lines in their spectra

  26. 1. Quasar redshift • Very Large, therefore very far away • Very bright AGN

  27. 2. Looking back in time • Several billion ly away • Observing a quasar is seeing it as it was a long time ago • If quasars are extra-bright galactic nuclei, then the many distant ones are nuclei of galaxies as they existed when the universe was young.

  28. b. Current theory suggests that quasars existed around supermassive black holes that pulled gas into the center, where in a violent swirl, friction heated the gas to extreme temperatures resulting in the bright light energy that was first detected.

  29. 3. Source of power The AGN and quasars emit far more energy than ordinary galaxies, but they are as small as solar systems. This suggests that all of these objects are supermassive black holes.

  30. The beams of charged particles that stream out of the cores of radio galaxies and form jets are probably created by magnetic forces. As material falls into a black hole, the magnetic forces push the charged particles out into jets. There is evidence that similar beams or jets occur in other types of AGN and in quasars.

  31. Finding galaxies with different shapes reveals the past, present, and future of the universe. • Galaxies can be elliptical, disk-shaped, or irregular. • Galaxies range in mass from 1 million Suns to more than a trillion Suns.

  32. Many galaxies seem to be organized in groups called clusters. • Quasars are the nuclei of faraway galaxies that are dim and seen as they were long ago, due to their great distances. • Hubble’s law helped astronomers discover that the universe is expanding.

  33. How were Edwin Hubble’s discoveries about redshifts used to conclude that the universe is expanding? Answer: Hubble found that the redshift of a galaxy depended on its distance from Earth. The more distant a galaxy is, the greater its redshift; that is, the faster it is moving away. This implies that the universe is expanding.

  34. What could be defined as the velocity at which a galaxy is moving away from Earth, divided by its distance from Earth? Answer: the Hubble constant

  35. What are active galactic nuclei? Answer: Active galactic nuclei are the cores of galaxies that emit exceedingly large amounts of energy from their centers.

  36. How might active galactic nuclei and quasars be related? Answer: Today’s active galactic nuclei might be former quasars that are not as energetic as they were billions of years ago.

  37. What is a radio galaxy? Answer: A radio galaxy is one that emits as much or more energy in radio wavelengths than it does in wavelengths of visible light.

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