1. Charles Hakes Fort Lewis College1

2. Charles Hakes Fort Lewis College2 Chapter 14 Variable Stars The Milky Way

3. Charles Hakes Fort Lewis College3 Outline Variable Stars The Milky Way Dark Matter Review Questions

4. Charles Hakes Fort Lewis College4 Lab Notes “Extra” group labs due Today. Star/constellation ID lab. Telescope lab? Observatory Field Trip(s) Wednesday (?) Thursday (?) with sign up. Dress very warmly - temperature drops fast!

5. Charles Hakes Fort Lewis College5 For waves, their velocity is the product of: A) frequency times wavelength B) period times energy C) frequency times period D) amplitude times wavelength E) amplitude times frequency

6. Charles Hakes Fort Lewis College6 For waves, their velocity is the product of: A) frequency times wavelength B) period times energy C) frequency times period D) amplitude times wavelength E) amplitude times frequency

7. Charles Hakes Fort Lewis College7 Which of these does not exist? A) a six solar mass black hole B) a million solar mass black hole C) a 3.8 solar mass neutron star D) a.06 solar mass brown dwarf E) a 1.3 solar mass white dwarf

8. Charles Hakes Fort Lewis College8 Which of these does not exist? A) a six solar mass black hole B) a million solar mass black hole C) a 3.8 solar mass neutron star D) a.06 solar mass brown dwarf E) a 1.3 solar mass white dwarf

9. Charles Hakes Fort Lewis College9 Variable Star Observations Some stars appear to change in brightness in a very regular way.

10. Charles Hakes Fort Lewis College10 Figure 14.4c Variable Stars - Cepheid example

11. Charles Hakes Fort Lewis College11 Figure 14.4ab Variable Stars RR Lyrae light curve Cepheid light curve

12. Charles Hakes Fort Lewis College12 Variable Star Observations RR Lyrae and Cepheid variables are types of variable stars. The brightness varies in a very regular way The stars can be recognized and identified by observing the light variations http://cfa-www.harvard.edu/~jhartman/M3_movies.html

13. Charles Hakes Fort Lewis College13 Figure 14.5 Variable Stars on the H–R Diagram Once identified, the luminosity (absolute magnitude) is known.

14. Charles Hakes Fort Lewis College14 Figure 14.6 Period–Luminosity Plot

15. Charles Hakes Fort Lewis College15 Variable Star Observations Globular clusters contain many RR Lyrae variables, so their distances can be determined.

16. Charles Hakes Fort Lewis College16 Figure 14.8 Globular Cluster Distribution The center of the Milky Way can be estimated by observing the center of all globular clusters. Diameter of this halo is ~30 kpc (kilo- parsecs)

17. Charles Hakes Fort Lewis College17 Figure 14.9 Stellar Populations in our Galaxy

18. Charles Hakes Fort Lewis College18 Variable Star Observations Cepheid variables are so bright that they can be seen in neighboring galaxies. We can therefore determine the distances to those galaxies.

19. Charles Hakes Fort Lewis College19 Figure 14.7 Variable Stars on Distance Ladder Greater distances can be determined than typically available through spectroscopic parallax, because these variables are so bright.

20. Charles Hakes Fort Lewis College20 You observe two Cepheid variable stars. Star A has a period of 10 days. Star B has a period of 30 days. Which is more luminous? A) A B) B C) they are the same D) not enough information

21. Charles Hakes Fort Lewis College21 You observe two Cepheid variable stars. Star A has a period of 10 days. Star B has a period of 30 days. Which is more luminous? A) A B) B C) they are the same D) not enough information

22. Charles Hakes Fort Lewis College22 You observe Cepheid stars in two different galaxies (A and B). They have the same apparent brightness. Star in galaxy A has a period of 10 days. Star in galaxy B has a period of 30 days. Which galaxy is closer? A) A B) B C) they are the same distance D) not enough information

23. Charles Hakes Fort Lewis College23 You observe Cepheid stars in two different galaxies (A and B). They have the same apparent brightness. Star in galaxy A has a period of 10 days. Star in galaxy B has a period of 30 days. Which galaxy is closer? A) A B) B C) they are the same distance D) not enough information

24. Charles Hakes Fort Lewis College24 Mapping the Milky Way

25. Charles Hakes Fort Lewis College25 Chapter 14 Spiral Galaxy - NGC 4603

26. Charles Hakes Fort Lewis College26 Chapter 14 Spiral Galaxy - 7331

27. Charles Hakes Fort Lewis College27 Figure 14.1 Galactic Plane

28. Charles Hakes Fort Lewis College28 Figure 14.2a Spiral Galaxies - The Andromeda galaxy is the Milky Way ’ s big sister. Distance ~800kpc

29. Charles Hakes Fort Lewis College29 Figure 14.2bc Spiral Galaxies A view of spiral galaxies from face- on and edge-on.

30. Charles Hakes Fort Lewis College30 Figure 14.3 Herschel ’ s Galaxy Model early attempt to map the galaxy by simply counting stars in a given direction.

31. Charles Hakes Fort Lewis College31 Mapping the Milky Way Radio observations can determine much of the structure and rotation rates.

32. Charles Hakes Fort Lewis College32 Figure 14.10 Observations of the Galactic Disk

33. Charles Hakes Fort Lewis College33 Mapping the Milky Way Radio observations can determine much of the structure and rotation rates. Orderly rotation in the plane. Random orbits in the halo.

34. Charles Hakes Fort Lewis College34 Figure 14.12 Stellar Orbits in Our Galaxy

35. Charles Hakes Fort Lewis College35 Figure 14.13 Milky Way Formation Recall solar system formation. Halo objects formed before the gas and dust fell to a plane.

36. Charles Hakes Fort Lewis College36 Mass of the Milky Way Recall Newton’s modification to Kepler’s third law:

37. Charles Hakes Fort Lewis College37 Figure 14.18 Galaxy Rotation Curve

38. Charles Hakes Fort Lewis College38 Mass of the Milky Way There is apparently more mass than can be seen. Unseen mass out to ~50 kpc. Recall radius of observable Milky Way is ~15 kpc. Dark Matter Can detect gravitational effects Cannot detect any other way.

39. Charles Hakes Fort Lewis College39 Dark Matter Is not atomic or molecular clouds - we would detect those using spectroscopy. Could be brown dwarfs or white dwarfs - very difficult to see. MACHOs - MAssive Compact Halo Objects Could be exotic subatomic particles WIMPs - Weakly Interacting Massive Particles

40. Charles Hakes Fort Lewis College40 Figure 14.19 Gravitational Lensing

41. Charles Hakes Fort Lewis College41 Review Questions

42. Charles Hakes Fort Lewis College42 A star has an apparent magnitude of +1.0 and an absolute magnitude of +1.0. If the distance between Earth and the star increases, the apparent magnitude would _____, and the absolute magnitude would _____. A) increase; decrease B) decrease; increase C) increase; not change D) decrease; not change E) not change; increase

43. Charles Hakes Fort Lewis College43 A star has an apparent magnitude of +1.0 and an absolute magnitude of +1.0. If the distance between Earth and the star increases, the apparent magnitude would _____, and the absolute magnitude would _____. A) increase; decrease B) decrease; increase C) increase; not change D) decrease; not change E) not change; increase

44. Charles Hakes Fort Lewis College44 Using spectroscopic parallax, you find a star’s distance to be 76 parsecs. You now find out that the star isn’t a main sequence star, but is a red giant. Your distance estimate is A) too large B) too small C) fine - no significant change in estimate is needed.

45. Charles Hakes Fort Lewis College45 Using spectroscopic parallax, you find a star’s distance to be 76 parsecs. You now find out that the star isn’t a main sequence star, but is a red giant. Your distance estimate is A) too large B) too small C) fine - no significant change in estimate is needed.

46. Charles Hakes Fort Lewis College46 A star has apparent magnitude of +8.0 before it goes nova and increases its luminosity by 10,000 times. Its apparent magnitude after it goes nova is. A) +8.0 B) +18.0 C) -8.0 D) -2.0 E) +3.0

47. Charles Hakes Fort Lewis College47 A star has apparent magnitude of +8.0 before it goes nova and increases its luminosity by 10,000 times. Its apparent magnitude after it goes nova is. A) +8.0 B) +18.0 C) -8.0 D) -2.0 E) +3.0

48. Charles Hakes Fort Lewis College48 Which is correct? 1 - The new moon rises at noon. 2 - The first quarter moon rises at noon. 3 - The full moon rises at noon. 4 - The third quarter moon rises at noon.

49. Charles Hakes Fort Lewis College49 Which is correct? 1 - The new moon rises at noon. 2 - The first quarter moon rises at noon. 3 - The full moon rises at noon. 4 - The third quarter moon rises at noon.

50. Charles Hakes Fort Lewis College50 In Paris, France (50 degrees north latitude), what is the longest day of the year? 1: March 21 2: June 21 3: September 21 4: December 21

51. Charles Hakes Fort Lewis College51 In Paris, France (50 degrees north latitude), what is the longest day of the year? 1: March 21 2: June 21 3: September 21 4: December 21

52. Charles Hakes Fort Lewis College52 Where along the horizon does the Sun rise on June 21 in Paris, France? 1: Due east 2: North of east 3: South of east 4: Can’t tell with information given

53. Charles Hakes Fort Lewis College53 Where along the horizon does the Sun rise on June 21 in Paris, France? 1: Due east 2: North of east 3: South of east 4: Can’t tell with information given

54. Charles Hakes Fort Lewis College54 Review What was the most important thing you learned? Toast could become a black hole… With fusion, iron is a dead end. Elements heavier than iron require energy input for creation. The sun was created from “enriched” interstellar dust neutron stars are about 20 km in diameter, and rotate very quickly.

55. Charles Hakes Fort Lewis College55 Review What questions do you still have about today’s topic? How do you detect a black hole?

56. Charles Hakes Fort Lewis College56 Review What was the most important thing you learned? If the surface gravity is so high that light can’t escape, then it is a black hole. Any object has a radius that if it is compressed below that radius, light cannot escape. Schwarzchild radius is 3km x M(solar) Center of the milky way could be a very massive black hole We can see black holes when things accelerate and fall into them. When charged particles start orbiting a black hole, they radiate in x-rays.

57. Charles Hakes Fort Lewis College57 Review What was the most important thing you didn’t learn? If the Earth fell into a black hole it would still orbit the same ?

58. Charles Hakes Fort Lewis College58 Review What questions do you still have about today’s topics? What is solar mass? Something with the same mass as the Sun. Is it just a myth that black holes suck stuff in? Gravitational force is the same, if distance and mass is the same. If the sun were replaced by a black hole, the planets would not fall in. How many supernovas explode each year? A supernova happens once per century – we are due. Can we send something into a black hole?

59. Charles Hakes Fort Lewis College59 Three Minute Paper Write 1-3 sentences. What was the most important thing you learned today? What questions do you still have about today’s topics?