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Andromeda galaxy M31

Andromeda galaxy M31. Milky Way galaxy similar to M31. Model of Milky Way, diameter 100,000 ly. Central bulge radius 6,000 ly. Thickness of spiral arms 2,000 ly. Globular cluster. Nebula. Open cluster. Sun location is in spiral arm, 2/3 from the center to the edge. Fig. 15-10a, p.299.

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Andromeda galaxy M31

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  1. Andromeda galaxy M31 Milky Way galaxy similar to M31

  2. Model of Milky Way, diameter 100,000 ly Central bulge radius 6,000 ly. Thickness of spiral arms 2,000 ly Globular cluster Nebula Open cluster Sun location is in spiral arm, 2/3 from the center to the edge Fig. 15-10a, p.299

  3. Size: diameter 100,000 ly, thickness of spiral arms 2,000 ly (2%). Radius of bulge ~ 5,000 ly Contains 2 × 1011 stars. Mass 4 × 1011 M. Nebula (~25% by mass), open clusters in spiral arms, 135 globular clusters in the galactic halo, central black hole has 2.6 × 106 solar masses. Velocity of rotation about 220 km/sec. About half the mass is dark matter (matter that exerts gravity, but is invisible). Location of the Sun about 2/3 from center to edge in spiral arm. Halfway in the thickness part of spiral arm. Milky Way Galaxy

  4. TYPES OF GALAXIES Spiral (Spiral Bar) 10% Mass 0.1 to 10 times Milky Way Elliptical 80%; Mass 0.001 to 50 Milky Way Irregular 5% Mass < 0.01 Milky Way Peculiar (active) – Radio galaxy, quasar, etc. GALAXIES

  5. Elliptical galaxies: E0 to E7. E0 is spherical and E7 highly elliptical in shape. Contains very old, relatively less massive stars and have very little gas and dust. Most common galactic type. • Spiral galaxies: have central bulge and spiral arms. Have lots of gas and dust, mostly in the spiral arms. Spiral bar SB have a bar attached to central bulge. • Irregular galaxies: no particular shape but has lots of gas and dust. Typically smaller in mass than spiral galaxies. About few per cent of galaxies are irregular. • Active (peculiar) galaxies, such as quasars. Few in numbers.

  6. Active (peculiar) Galaxies: • Radio galaxies: Radio galaxies emit enormous amount of radio waves, • typically much farther than the corresponding optical galaxy. • Radio galaxies usually are double lobed and have jets of particles • emitted from the nucleus of the galaxy. • When the jet of particles interacts with intergalactic matter, • radio waves are created. • Quasars: Quasars are near the edge of the Universe. Very bright. • Large redshift z > 0.1; small in size. • Some give out enormous amount of radio waves. • Seyfert galaxies are somewhat between quasars and normal galaxies. • Distance distribution of quasars tells us that the universe has an edge. • From gravitational lensing of quasars by an in-between galaxy in our • line of sight, distances can be estimated and quasars are indeed • very far away. • Most galaxies have supermassive black holes in their center. • The larger the mass of the black hole, the larger is the central bulge • of the galaxy.

  7. Radio galaxy Cygnus A Optical ^ Fig. 17-2, p.344

  8. Fig. 17-3, p.344

  9. Centaurus An elliptical galaxy-strong radio source Fig. 17-4a, p.344

  10. Redshift z = Δλ/λ Quasar redshift z=0.17 p.342

  11. Centaurus A in X-ray Fig. 17-4b, p.344

  12. Quasars – Size is small ~ 0.1 ly. A large object can’t appear to fluctuate in brightness as rapidly as a smaller object. For example an object abruptly brightens at one instant. The wave emitted from the edge of the object takes longer to reach the observer than light from the near side of the object, because it has to travel farther. We don’t see the full variation until waves from all parts of the object reach us. Fig. 17-13, p.350

  13. Four quasars. Quasars appeared star like (i.e. points) but with very large Doppler shift. With bigger telescopes many quasars now have structure, such as spiral arms. Fig. 17-6, p.346

  14. Next to most distant Quasar. Now largest z = 10 Fig. 17-11a, p.348

  15. Fig. 17-14, p.351

  16. Quasar overexposed shows galaxy structure Fig. 17-19, p.353

  17. Sloan Digital Sky Survey 2° Field Universe has an edge! Fig. 17-20a, p.353

  18. Universe has an edge. Fig. 17-20b, p.353

  19. Interacting and colliding quasars Fig. 17-21, p.354

  20. NGC 4258 has very bright center. A black hole Fig. 17-23, p.355

  21. HST of M87. Galaxy nucleus is on top Fig. 17-24a, p.356

  22. M87 Has a 3×109M Black Hole in the center

  23. M87 nucleus Fig. 17-24b, p.356

  24. Sagittarius A center of Milky Way Very small size and strong radio waves Fig. 17-26b, p.357

  25. The larger the central bulge, the more massive the black hole Fig. 17-27, p.358

  26. Black Hole – mass 1 × 109 M

  27. Fig. 17-30, p.360

  28. Fig. 17-34, p.362

  29. Gravitational lensing of two quasars. Distance can be computed. Fig. 17-33, p.361

  30. The two Quasar images are identical. Gravitational lensing. Fig. 17-33a, p.361

  31. Einstein ring from gravitational lensing. Fig. 17-35a, p.362

  32. Radio galaxies. Few in number, but enormous amount of radio energy emitted. The source of the radio waves is up to a million light years from the optical part. Quasars. Not all emit radio waves. Very compact (~0.1 ly), very bright compared to normal galaxies. Found near the edge of the Universe. Some have spiral arms. Seyferts. In between quasars and spiral galaxies. Summary

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