Observations of Milky Way Dwarf Spheroidal galaxies with the Fermi ...
Chapter 30 Notes Galaxies and the Universe. The Milky Way Galaxy It is difficult to see the size and...
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Transcript of Chapter 30 Notes Galaxies and the Universe. The Milky Way Galaxy It is difficult to see the size and...
The Milky Way Galaxy
• It is difficult to see the size and shape of the Milky Way from our perspective (inside it)
• Every star we can see is part of the Milky Way
Milky Way: Size and Shape
• Variable stars in globular clusters help to determine the size and shape of the galaxy
• From the side, it looks something like a fried egg
Milky Way Galaxy: Spiral Arms
• 4 major arms, several minor arms
• About 100 billion stars in the disk
• Galaxy halo: older, dimmer stars
• Center: supermassive black hole
Population I and II Stars
• Population I: Younger stars like the Sun found mostly in the disk and spiral arms; about 2% heavy elements
• Population II: Older stars found in the halo or nuclear bulge; minimal amounts of elements heavier than helium
The Milky Way Galaxy
• The spiral arms do not rotate as a unit
• Spiral density wave hypothesis: traffic jam analogy
Other Galaxies
• First one (Andromeda) discovered in 1924 by Edwin Hubble
• Mass of other galaxies is dominated by mysterious subatomic particles called dark matter
• The Milky Way is part of a group of about 40 other galaxies: the Local Group
The Expanding Universe
• Another discovery by Hubble (1929) made by measuring the “redshift” of galaxies: – All distant galaxies are moving away from Earth– The farther away a galaxy is, the faster it is moving
away– The entire universe is expanding
• Extrapolating backward: at one time, all matter in the universe was compressed together
The Big Bang
• Not an explosion—an expansion of the universe from a single point called the singularity
• Further evidence: “fossil” radiation (cosmic background radiation)
Possibilities for the Future of the Universe
• Flat: The expansion of the universe will slow down and stop
• Closed: The universe will begin to contract
• Open: The universe will continue to expand forever