2. Simulated black hole picture

3. VLA
27 telescopes New Mexico

4. Event Horizon Telescope

9. Wormholes
Tunnels through spacetime.

13. Exam Tuesday Covers reading and related notes from chapters
14.1, 14.2, 15-18, S2 & S3
Same format as last time.
One sheet of notes with writing on one side

14. The Milky Way

15. Milky Way (all sky image)

16. Herschel’s view of Milky Way

17. M13 Hercules

18. Discussion
How can we determine the distances to globular clusters? All the globular clusters are too far away to get parallax distances.

19. Main sequence fitting

22. Main-Sequence fitting
Match the band of main-sequence stars with another H-R diagram plotted with temp. and luminosity.

23. RR Lyrae stars
The most accurate way to measure the distance to globular clusters is by measuring the period of the RR Lyrae stars.

26. Discussion
Why is the pulsation period related to the luminosity?

28. Discussion
Why can’t we just use the higher luminosity Cepheids to find the distance to globular clusters?

30. The results
The globular clusters are centered around a point 8 kpc from the Sun in the direction of Sagittarius.

33. Discussion
Why did Herschel get the wrong answer for distribution of stars in the galaxy?

34. Interstellar absorption
The galaxy contains large amounts of dust and gas in the galactic plane that obscures stars.

37. Discussion
What observations could you make to either prove or disprove this conclusion that dust is a problem in mapping the distribution of stars in our galaxy?

38. MW in infrared light
MW in microwave

40. Discussion
If you wanted to map out the hydrogen gas in the galaxy, how might you go about doing it?
What are the disadvantages of your method?

44. HI neutral Hydrogen map

46. Stellar populations
Bulge
Thin disk
Thick disk
Halo

47. Disk stars Metal rich stars like the Sun, often referred to as population I.
Thin disk stars typically stay within 200 pc of the galactic plane, whereas thick disk stars stay with 1 kpc.
Buldge stars -- Metal poor stars, often called population II stars, that tend to be lower mass red stars.
Halo stars -- Can be metal poor or metal rich.
They occupy a sphere surrounding the galaxy, having random orbits far from the galactic center and high velocities relative to the Sun.

52. Discussion
The Sun, traveling at 220 km/sec takes about 230 million years to complete one orbit around the galaxy. How could we measure the motion of the Sun about the galactic center?
Hint: It involves the random distribution of the globular clusters

53. H and He stars contain about 75% hydrogen and 24% helium
the universe once contained only hydrogen and helium
metals come from supernova explosions

55. Discussion
What do you think happens to the amount of material in the interstellar medium over time?

56. Discussion
Do you think the amount of metals within a star can be used to determine the age of a star? What assumptions would you need to make? What observations could you make to determine if these assumptions hold?

57. Metal content does not equal age!
Galaxies appear to go through episodic periods of star formation.

58. Discussion
In general, astronomers speak of disk stars as being younger and bulge and halo stars as being older. Although an over-simplification, how do you know that this is true? What do you need to have a young population of stars?

60. Rotation curve of Milky Way
Plot of orbital speed verses distance from the center

61. Discussion
A rotation curve is a plot the rotational velocity vs. distance from the center of the rotating object. If you plot the rotation curve of a rotating disk, or a merry-go-round, what would the plot look like?

64. Discussion
What would the rotation curve of the planets in the solar system look like?

67. Discussion
What should the rotation curve of the galaxy look like?

69. Actual rotation curve
The actual rotation curve of the galaxy is flat. The stars near the Sun move at a nearly constant velocity of 230 km/s regardless of distance from the galactic center.

72. Discussion
The rotation curve of the galaxy is not perfectly flat. What do you think causes the bumps in the rotation curve?

75. Milky Way