Questions for Chapter 19

1. What is this? [picture is in the infrared]

2. Draw simple sketches of our galaxy as it would appear face-on and edge-on. Identify the disk, bulge, halo, and spiral arms, and indicate the galaxy's approximate dimensions.

3. What are the Large and Small Magellanic Clouds, and the Sagittarius and Canis Major Dwarfs?

4. Describe the basic characteristics of stellar orbits in the bulge, disk, and halo of our galaxy.

5. How can we use orbital properties to learn about the mass of the galaxy? What have we learned?

6. Summarize the star-gas-star cycle.

7. What creates a bubble of hot ionized gas? What happens to the gas in the bubble over time?

8. What do we mean by atomic hydrogen gas? How common is it, and how do we map its distribution in the galaxy?

9. Briefly summarize the different types of gas present in the disk of the galaxy, and describe how they appear when we view the galaxy in different wavelengths of light.

10. What are ionization nebulae, and why are they found near hot, massive stars?

11. How do we know that spiral arms do not rotate like giant pinwheels? What makes spiral arms bright?

12. What triggers star formation within a spiral arm? How do we think spiral arms are maintained?

13. What characteristics distinguish disk population stars from spheroidal population stars?

14. The average speed of stars in the solar neighborhood relative to the Sun is about 20 km/s (this is the speed at which we see the stars moving toward or away from the Sun not their orbital speed around the galaxy). Suppose you discover a star in the solar neighborhood that is moving relative to the Sun at a much higher speed, say, 200 km/s. What kind of orbit doe~ this star probably have around the Milky Way? In what part of the galaxy does it spend most of its time? Explain.

15. Why have stars ceased to form in globular clusters long ago? Why are globular clusters are deficient in elements heavier than hydrogen and helium?

16. Suppose you discover a star made purely of hydrogen and helium. How old do you think it would be? Explain your reasoning

17. How do the different ages of disk stars and halo stars support the idea that our galaxy formed from the gravitational collapse of a protogalactic cloud?

18. What evidence suggests that the Milky Way's full protogalactic cloud formed from the merger of smaller protogalactic clouds?

19. What is Sgr A*? What evidence suggests that it contains a massive black hole?

20. What is the future of our Galaxy?

21. What is happening at the galactic center? 

Decide whether the statement makes sense (or is clearly true) or does not make sense (or is clearly false). Explain clearly; not all these have definitive answers, so your explanation is more important than your chosen answer.

22. We did not understand the true size and shape of our galaxy until NASA launched satellites into the galactic halo, enabling us to see what the Milky Way looks like from the outside.

23. Planets like Earth probably didn't form around the very first stars because there were so few heavy elements back then.

24. Many spectacular ionization nebulae are seen throughout the Milky Way's halo.

25. The carbon in my diamond ring was once part of an interstellar dust grain.

26. The Sun's velocity around the Milky Way tells us that most of our galaxy's dark matter lies in the galactic disk near the center of the galaxy.

27. We know that a black hole lies at our galaxy's center because numerous stars near it have vanished over the past several years, telling us that they've been sucked in.

28. If we could watch a time-lapse movie of a spiral galaxy over millions of years, we'd see many stars being born and dying within the spiral arms.

29. The star-gas-star cycle will keep the Milky Way looking just as bright in 100billion years as it looks now.