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

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

YOU ARE HERE… The Sun is located on the Orion Arm of the Milky Way 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. 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. ~10,000 parsecs from the center of the galaxy.

How huge is the Milky Way? Milky Way Dimensions: 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 Solar Masses “If there’s a bright center to the galaxy, you’re on the planet that it’s farthest from. “ ~Luke Skywalker, Star Wars 3,300 LY 75,000 LY SUN 33,000 LY

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

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. 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! It takes about 240 million years for the Sun to orbit the center of the galaxy!

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

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

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

Hubble Deep Field: Millions of Galaxies!

Elliptical Galaxies Spheres or Ellipses

Spiral Galaxies

Barred Spirals

Irregular Galaxies

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

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

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