Lecture 32 Properties of the Milky Way cont

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Lecture 32- Properties of the Milky Way (cont)

• Spiral patterns and rotation curves

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Spiral Patterns

• Does the Milky Way have spiral arms?
• What causes them?
• http//antwrp.gsfc.nasa.gov/apod/ap020620.html
• M81 (binocular object in Ursa Major)

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Spiral Arms in the Milky Way

• Measure distances to large number of objects (HII
  regions, star clusters, etc) and map them up
• Transparency

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What are the spiral patterns?

• Not beads on a wire
• It is a wave propagating through the gas of the
  galactic disk
• Slinky model
• Molecular clouds, young stars, star formation
  regions tend to be concentrated in spiral arms

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All large disk galaxies have spiral structure to
some degree
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Next topic rotation curves.

• How is mass distributed in a galaxy?
• What is a galaxy made of?