Andromeda galaxy M31

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Andromeda galaxy M31
Milky Way galaxy similar to M31
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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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Milky Way Galaxy

• 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.

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GALAXIES

• 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 lt 0.01 Milky Way
• Peculiar (active)
• Radio galaxy, quasar, etc.

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• 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.

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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 gt 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.
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Radio galaxy Cygnus A
Optical
Fig. 17-2, p.344
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Fig. 17-3, p.344
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Centaurus An elliptical galaxy-strong radio source
Fig. 17-4a, p.344
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Redshift z ??/?
Quasar redshift z0.17
p.342
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Centaurus A in X-ray
Fig. 17-4b, p.344
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Quasars Size is small 0.1 ly.
A large object cant 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 dont see the full
variation until waves from all parts of the
object reach us.
Fig. 17-13, p.350
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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
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Next to most distant Quasar. Now largest z 10
Fig. 17-11a, p.348
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Fig. 17-14, p.351
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Quasar overexposed shows galaxy structure
Fig. 17-19, p.353
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Sloan Digital Sky Survey 2 Field Universe has an
edge!
Fig. 17-20a, p.353
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Universe has an edge.
Fig. 17-20b, p.353
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Interacting and colliding quasars
Fig. 17-21, p.354
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NGC 4258 has very bright center. A black hole
Fig. 17-23, p.355
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HST of M87. Galaxy nucleus is on top
Fig. 17-24a, p.356
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M87 Has a 3109M? Black Hole in the center
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M87 nucleus
Fig. 17-24b, p.356
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Sagittarius A center of Milky Way Very small size
and strong radio waves
Fig. 17-26b, p.357
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The larger the central bulge, the more massive
the black hole
Fig. 17-27, p.358
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Black Hole mass 1 109 M?
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Fig. 17-30, p.360
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Fig. 17-34, p.362
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Gravitational lensing of two quasars. Distance
can be computed.
Fig. 17-33, p.361
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The two Quasar images are identical. Gravitation
al lensing.
Fig. 17-33a, p.361
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Einstein ring from gravitational lensing.
Fig. 17-35a, p.362
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Summary

• 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.