Sci. 4-3 Galaxies

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Sci. 4-3 Galaxies Pages 110-113
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A. Galaxies- large groupings of stars in space
held together by the attraction of gravity
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B. Edwin Hubble classified galaxies according to
their shape. Major types include spiral,
elliptical, and irregular galaxies.
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1) Spiral galaxies- have a bulge at the center
and very distinct spiral arms, a) Most galaxies
are this type of galaxy.
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b) The Milky Way is a spiral galaxy.
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• Elliptical Galaxies- massive blob of stars shaped
  from sphere shape to cucumber shape
• a) only contains old stars

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• Irregular Galaxies- galaxies that dont fit into
  the other classes.
• a) Many of these galaxies may have their shape
  distorted by neighboring galaxies gravity.

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• Nebula- giant clouds of gas and dust
• 1) Some nebulas are regions where new stars are
  formed from gas and dust

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D. Globular Cluster- groups of older stars that
look like a ball of stars 1) Globular stars
clusters are found in the halos of spiral
galaxies and in elliptical galaxies.
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E. Open Clusters- groups of stars that are
usually located along the spiral disk of a galaxy.
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• Origin of Galaxies
• 1) Because light travels at a certain speed,
  observing distant galaxies is looking back in
  time. Scientists look at distant galaxies to
  learn what early galaxies look like.

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• Quasars- a starlike source of light that is
  extremely far away
• 1) Quasar may be the earliest types of galaxies
  ever formed
• 2) Quasar may have enormous black holes at their
  center
• 3) Quasars are among the most powerful energy
  sources in the universe.