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Galactic Power Point

• Bause
• North Farmington High
• FPS

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The Milky Way

• Galileo Discovered
• William Herschel tried to count the number of
  stars in the Milky Way. Couldnt because
• Interstellar Medium- matter between stars that
  block/reflect/scatter light.
• 200 billion stars in our galaxy!!! So many, that
  without interstellar medium our sky would be as
  bright as noon all day long!!!

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Milky Way probably looks like this
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What you could see in dark skies
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3 ComponentsSee fig. 23.10

• Galactic Bulge- center of galaxy. Home of the
  super massive black hole.
• Galactic Disk- flat, planar disk containing most
  of the mass. Mostly hot blue stars.
• Galactic Halo- Sphere of old (red, cool) dim
  stars. Random orbits around center.

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• 100,000 l.y. across, 1000 l.y. thick (at sun) and
  13,000 l.y. thick at center.
• Distance from the center is 30,000 l.y.
• Sun is found near, but not on the Orion Arm--gt
  part of the milky way that appears to pass
  through the constellation Orion.
• Globular Clusters found in the halo. 1,000s of
  really old stars cluster together (10-12 bill yrs
  old).
• Bause Diagram

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Three new streams of stars were discovered
ringing the Milky Way. The two closest streams
are thought to be star clusters, while the huge
arcing stream is thought to be a dwarf galaxy.
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Galactic Disk

• LOTS of interstellar matter--gt gas and dust!!
• Due to tremendous amounts of gas, many stars are
  being created--gt young, hot, blue stars.
• Open star clusters form on disk--gt 100s of
  young, blue stars. (Pleides- 7 sisters)
• Stars of all ages are found on the disk.
• Nearly circular orbit
• Distance from center determines rate of
  revolution. Sun travels 220km/s
• Galactic Year-225 mil yrs

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Open Star Cluster Pleiades
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Galactic Disk
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Galactic Halo

• Little to no gas--gt no new stars being created.
• All old red stars (K or M) 10-12 billion yrs old.
  
• Globular clusters found in halo. 1,000-100,000
  old red star clusters.
• Orbit around center is very eccentric and
  random--gt rotate in ALL directions
• Bright star Arcturus is a bright giant literally
  passing through galactic disk.

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Globular Cluster M13 Hercules
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Galactic Center

• Football shaped
• Contains all ages of stars, ongoing star
  formation
• Random orbits (unlike disk), but not as eccentric
  as the halo.
• Yellow/white color.
• We cant see due to interstellar medium.
• Average of 50,000 stars per cubic parsec!!!
• Center More than 1 mil solar masses--gt super
  massive black hole

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Galactic Center
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Center of Milky Way
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Hubbles Galaxy Classification

• 4 types--gt Spiral, Barred Spiral, Elliptical and
  Irregular

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Spiral Galaxy
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Andromeda (M31)
NGC something
M32
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Spiral
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Elliptical Galaxy
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Elliptical Galaxies

• Have no disk. Can be nearly spherical to football
  shaped.
• No gas--gt no new star formation. Entirely made up
  of old stars. 10-12 bill yrs.
• Have a random orbital motion around the center.
  (similar to our Halo stars)
• Giant ellipticals can have trillions of stars!!!
• Can have a diameter 1 megaparsec (2-3 million
  light years!!!!!!!) Holy Shnikeys!!!!!

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Elliptical Galaxy M59 (near US 23 in Hartland)
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Irregular Galaxies

• No obvious structure. Sometimes have an explosive
  appearance.
• All ages of stars with current star formation due
  to abundant gas and dust.
• Irregular orbits (duh!).

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Irregular
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Whats this ???
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Whats this???
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Whats this?
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Whats this???
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Whats this?

• Edge-On galaxy NGC 891

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THE END!!! Remember theyre watching you!!!