A Long Time Ago in a Galaxy Far, Far Away…

1. A Long Time Ago in a Galaxy Far, Far Away…

2. The Milky Way Galaxy: Home Sweet Home!! • Our home Galaxy is called the MILKY WAY (like the candy bar ) • So named because early stargazers thought the stars looked like milk spilled across the sky.

3. YOU ARE HERE… • The Sun is located on the Orion Arm of the Milky Way • If you look toward the constellation Sagitarius, you are looking toward the center of the galaxy. • ~10,000 parsecs from the center of the galaxy.

4. SUN 3,300 LY 33,000 LY 75,000 LY How huge is the Milky Way? “If there’s a bright center to the galaxy, you’re on the planet that it’s farthest from. “ ~Luke Skywalker, Star Wars • Milky Way Dimensions: • 75,000 light years from end to end • 3,300 light years thick • ~33,000 light years from the center of the galaxy to the Sun • Mass: 4 x 1011 Solar Masses

5. Galactic Anatomy • NUCLEUS: Bright Center of the galaxy. • NUCLEAR BULGE: Flattened cloud about 3 pc in radius around center of the galaxy. • HALO: Area surrounding galaxy that contains some scattered globular clusters. • DISK: Contains most of the stars in the galaxy.

6. Jump to Hyperspace? • By looking at the radial velocities of surrounding stars, we can estimate the Sun’s velocity to be about 220 km/s. • It takes about 240 million years for the Sun to orbit the center of the galaxy!

7. Like Spinning a Pizza… • Clouds of hydrogen and helium from the Big Bang • Star motion within causes it to rotate and contract • Cloud begins to flatten into a disk • Older stars are left behind in the halo • The galaxy is now nearly flat

8. Spiral Arms • Home to hot bright stars (O and B) • Used to trace the path of our spiral arms • Star formation is continuously renewed in spiral arms

9. Journey to the Center • Nucleus is the most mysterious part • Evidence of a Supermassive Black Hole in Saggitarius: • High Intensity Radio Source • Orbits of surrounding objects • Huge Mass (2.6 million solar masses) • Small size (3 pc) • Event Horizon is smaller than a period! • Too massive to be the remains of a star: possibly formed when galaxy did

10. Hubble Deep Field:Millions of Galaxies!

11. Elliptical GalaxiesSpheres or Ellipses

12. Spiral Galaxies

13. Barred Spirals

14. Irregular Galaxies

15. Galactic Hugeness and Other Amazing Stuff • Mega parsec = 3.26 million light years! • Estimate distance using indicators (clusters, Cepheids, supernovae) • Dark Matter: Measured mass is much larger than predicted mass, Gravitational lensing • Massive Black Holes: evidence in orbits of stars in the center

16. When Galaxies Collide… • Formation of spiral arms • Distortion or tearing • Galactic Cannibalism • Firestorms of Star Formation • Galactic Mergers • High Speed Collisions

17. Local Group: Our Galaxy’s Neighbors Milky Way Galaxy • The Milky Way is one of about 35 galaxies that are clumped close together. This clump is called the LOCAL GROUP. M31: Andromeda Galaxy Small Magellanic Cloud M33: Triangulum Galaxy Large Magellanic Cloud