1. Chapter 23: Our Galaxy Our location in the galaxy Structure of the galaxy Dark matter Spiral arm formation Our own supermassive black hole

2. Our place in the galaxy: Early views

3. The problem: Interstellar Extinction

4. The solution: Globular clusters and variable stars

5. Variable stars

6. Observing the Milky Way

7. Structure of the Milky Way

8. Star orbits in the Milky Way

9. Stellar populations

10. Spiral arms

11. 21 cm radiation

12. The sky at 21 centimeters

13. Mapping the galaxy

14. The Milky Way

15. Rotation of the Milky Way

16. Sun’s orbital motion

17. Rotation curves

18. Dark matter

19. What is dark matter? We don’t know. This is actually one of the most important unanswered questions in modern astronomy. A few ideas: –MACHOS –neutrinos –WIMPS

20. MACHOs: MAssive Compact Halo Objects Dim, dark objects with masses < 1 M  –Brown dwarfs –White dwarfs –Black holes Search for MACHOs used gravitational lensing. Low mass MACHOs (10 -6 -0.1 M  ) not significant part of dark matter halo. MACHOs of 0.5 M  account for about half of dark matter. –What else is out there?

21. MACHO detection via gravitational lensing

22. Other dark matter candidates Neutrinos –If neutrinos are sufficiently massive and enough are present in the galaxy then it is possible they could be the missing dark matter. –Neutrino oscillations require that neutrinos have mass, but it is very small (~10 -10 m electron ). –Neutrinos must be part of dark matter, but it is unclear how much. WIMPs –Weakly Interacting Massive Particles –Predicted by some theories but not yet confirmed experimentally.

23. Formation of spiral arms

24. Density waves

27. Sagittarius A*