1. Galactic Nucleus

2. Mass of the Galaxy The orbit of clusters can be used to estimate the mass of the galaxy. –Same used for planets and binary stars The Milky Way galaxy has a mass of 1 trillion (10 12 ) M . –Most mass not at the center infrared image

3. Radiating Gas Dust obscures visible light from the center of the galaxy. –Radio waves instead

4. Infrared View Infrared light can also penetrate galactic dust.

5. Mass at the Center The motion of stars near the galactic center gives the mass of the galactic nucleus. –Newton’s universal gravity –2.6 million (10 6 ) M  –Due to supermassive black hole

6. Central Bar The galactic nucleus is bright and massive. Spiral arms draw the nucleus into a bar. The Milky Way is probably similar to M83.

7. Fermi Bubbles Gamma ray images show large bubbles of super hot gas. –Above and below disk –30,000 ly each way Possibly giant explosions near central black hole. –Still a mystery

8. Problem with Orbits We can estimate the “visible” mass of the Milky Way. –200 billion stars –Gas and dust –Black holes The orbits of stars require times the mass. –Dark matter