AST101 The Evolution of Galaxies

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AST101The Evolution of Galaxies
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Virgo Cluster
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Collisions of Galaxies

• Outside of Clusters (the field), most galaxies
  are spiral or irregular
• In dense clusters, the most massive galaxies are
  ellipticals
• Spirals in clusters tend to inhabit the periphery

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Formation of Galaxies

• Initially masses 106 M?
• Protogalaxies collided and merged to form larger
  galaxies.
• If there is a net angular momentum, a disk forms,
  giving a spiral galaxy

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Arp 220 the Antennae
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NGC 2207
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Collisions Today
The Sagittarius Dwarf galaxy
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Active Galactic Nuclei

• The center of the Milky Way is a 2x106 M? black
  hole.
• Bigger galaxies have more massive central black
  holes (up to 109 M?)
• Some just sit there
• Others are actively accreting matter (gas, stars)

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Active Galactic Nuclei

• Accretion proceeds through a disk
• Accreting gas orbits near the Schwarzchild radius
  (event horizon) of the black hole
• The gas heats up as potential energy is converted
  to kinetic energy (heat)
• We see bright X-ray sources

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M87 Virgo Cluster
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Relativistic Jets

• Accreting black holes emit jets of radiation at
  velocities near the speed of light

Radio Jet M87
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Radio Galaxies
?Cygnus A ?Centaurus A
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Quasars

• In 1963 Martin Schmidt puzzled over the spectrum
  of a 12th magnitude star-like radio source (a
  quasi-stellar object, or QSO)

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3C 273

• Redshift z 0.16 Distance 2.4 x 109 ly
• It is one of the most luminous objects in the
  universe

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Active Galactic Nuclei

• Quasars
• Blazars
• Liners
• Seyfert galaxies
• All involve matter infall into massive black
  holes.