Cerro Tololo Observatory in Chile, with Milky Way

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Cerro Tololo Observatory in Chile, with Milky Way
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Setting the Cosmic Distance Scale

• If Earth (13,000 km) ? sesame seed
• Sun size (140,000 km) ? soccer ball x 100
• Earths orbit (300 million km 2 AU ) ?
  Macmillan x 200
• Solar system (160 AU) ? downtown Ithaca x 80
• to Sirius (500,000 AU 2.5 parsec) ? North
  America x 3,000
• Milky Way galaxy (40,000 parsec) ? Earths orbit
  x 15,000
• If Milky Way ? frisbee
• to Andromeda (800,000 parsec) ? length of a car
  x 15
• to distant galaxy (1 billion parsec) ? to King
  Ferry x 1500
• to most distant quasar (30 billion LY) ? to
  Pennsylvania

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A Classic Spiral Galaxy, Seen Face-On
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The Andromeda Galaxy and its two companions
Messier 31 / New General Catalog 224
6 moons ? 3 arc-degrees a frisbee at 15 feet
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A galaxy and its companion M51 NGC 5195
The Sombrero Galaxy M104
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The Seyfert Galaxy M104 very hot core
M83 A barred spiral
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NGC 4565
NGC 3115 an elliptical
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Andromeda
Milky Way
Our Local Group of galaxies
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Galactic Cluster CL 09394713 pretty typical
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Hubble Deep Field, in constellation Fornax
1/20 moon ? 1.5 arc-minutes a dime at 75 feet
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Hubble Ultra Deep Field
Four times further away so 16 times fainter
1/10 moon 3 arc-minutes
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1 million galaxies seen, 200 billion known

• bluishness is Milky Way
• note thread-like filamentary structure
• strong evidence for galactic clusters
• voids may be gravitationally active dark matter

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Most Galaxies have VERY Flat rotation curves
Vera Rubin (1975) this is true WELL beyond the
visible rim of a galaxy (like twice as far or
more!!)
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How Does the Rotation Curve Tell Us About the
Matter Distribution in a Galaxy?

• Newton showed that the mass M underneath an
  object that moves at v at a distance d is M v2d
  ? the bigger M is, so too v
• Disc Model M (d2) d d3 reasonable for a
  uniform solid body
• Point-mass Model M (1/d) d constant
  reasonable for a point mass at the center
• Observed flat Rotation Curve since v constant
  M d implies mass is concentrated near
  center, but not as a solid body
• one can make a more detailed analysis to get the
  mass distribution
• Fritz Zwicky (1933) studied the Coma Cluster and
  showed that the outer stars move MUCH faster than
  could be explained by the observed mass of the
  inner stars
• There had to be 400 times as much matter as was
  visible!!

Missing Mass Problem DARKMATTER
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Hubble Space Telescope Film of Coma Cluster

• outer stars are moving much too fast ? theres
  much more INVISIBLE matter near the clusters core

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Gravitational Lensing causes false arc-like images
nearby galaxy
eye
distant galaxy
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Gravitational Lensing of Distant Objects
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May 21 2007 Syracuse Post-Standard
Hubble Image of CL 002417
The blue streaks are very distant objects,
gravitationally lensed by the dark matter in the
nearby cluster