The Milky Way and other galaxies
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The Milky Way and other galaxies
Orion: star formation
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Galaxy
• A collection of millions or billions of stars
• 100 billion galaxies or more may exist (1010 galaxies, each with 1010 stars)
We live in the Milky Way galaxy
Galaxy M73
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The Milky Way
• Our solar system is near the outer edge of the milky way galaxy
• Because we are inside the Milky Way we can not see what it looks like from the outside.
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Clusters
• Gravity pulls galaxies together
• Our ‘Local Group’
contains the Milky Way, Andromeda, and 30 other galaxies
Superclusters : the largest structure in the Universe, 1 million light years across
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3 Types of galaxies• Spiral: has a bulge in
the center, with radiating arms and older stars are in the center, younger stars in arms
• Elliptical: spherical or egg- shaped, mostly older stars, reddish color
• Irregular: don’t have a defined structure
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How galaxies begin
• The deeper into space we look, the farther back in time we see.
• Quasars, the most distant and radiant objects in space, may be the centers of young galaxies.
• They may have black holes at their centers
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• Younger galaxies are blue
• Colors change as the gas and dust are consumed, and the stars cool
• Galaxies can collide,
changing their shape and generating new stars
• Older galaxies are red
I Zwicky 18 : young galaxy
How galaxies evolve
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How galaxies age
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Colliding galaxies
• NGC 6242 are galaxies that are circling each other.
• The colored centers are black holes
• At some point, they will merge
Photo by Keck observatory
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Relative sizes of galaxies
Review
1. What are clusters?
2. What are the 3 types of galaxies?
3. What may be at the center of young galaxies?