End of Chapter Questions

Review Questions

Question 11.1

1. Consider a star behind a cloud of interstellar gas and dust and at rest as seen from our perspective. Which of the following statements is correct?

  1. The star appears brighter than it would if the cloud were not present.

  2. The star appears to be blueshifted.

  3. The star appears redder than it would if the cloud were not present.

  4. The star would be invisible at all wavelengths.

  5. The star would always appear green.

Question 11.2

2. What is the lowest mass that a star can have on the main sequence?

  1. There is no lower limit.

  2. 0.003 M⊙

  3. 0.08 M⊙

  4. 0.4 M⊙

  5. 2.0 M⊙

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Question 11.3

3. What is the source of energy that enables a main-sequence star to shine?

  1. Friction between its atoms

  2. Fusion of hydrogen in a shell that surrounds the core

  3. Fusion of helium in its core

  4. Fusion of hydrogen in its core

  5. Burning of gases on its surface

Question 11.4

4. What are giant molecular clouds, and what role do they play in star formation?

Question 11.5

5. Why are low temperatures necessary for dense cores to form and contract into protostars?

Question 11.6

6. Why do thermonuclear reactions not occur on the surface of a main-sequence star?

Question 11.7

7. What is an evolutionary track, and how do such tracks help us interpret the H-R diagram?

Question 11.8

8. Draw the pre–main-sequence evolutionary track of the Sun on an H-R diagram. Briefly describe what occurred throughout the solar system at various stages along this track. (You may find it useful to review Chapter 10.)

Question 11.9

9. On what grounds are astronomers able to say that the Sun has about 5 billion years remaining in its main-sequence stage?

Question 11.10

10. What will happen inside the Sun 5 billion years from now when it begins to evolve into a giant?

Question 11.11

11. How is the evolution of a main-sequence star with less than 0.4 M⊙ fundamentally different from that of a main-sequence star with more than 0.4 M⊙?

Question 11.12

12. Draw the post–main-sequence evolutionary track of the Sun on an H-R diagram up to the point when the Sun becomes a helium-fusing giant. Briefly describe what might occur throughout the solar system as the Sun undergoes this transition.

Question 11.13

13. What does it mean when an astronomer says that a star “moves” from one place to another on an H-R diagram?

Question 11.14

14. What is the helium flash and what causes it?

Question 11.15

15. Explain how and why the turnoff point on the H-R diagram of a cluster is related to the cluster’s age.

Question 11.16

16. Why do astronomers believe that most globular clusters are made of old stars?

Question 11.17

17. What are Cepheid variables, and how are they related to the instability strip?

Question 11.18

18. What occurs in Cepheid stars that is analogous to the vapor raising the lid on a pot of boiling water?

Question 11.19

19. What are RR Lyrae variables, and how are they related to the instability strip?

Question 11.20

20. What is a Roche lobe, and what is its significance in close binary systems?

Question 11.21

21. What are the differences between detached, semidetached, contact, and overcontact binaries?

Advanced Questions

Question 11.22

22. How is a degenerate gas different from an ordinary gas?

Question 11.23

23. If you took a spectrum of a reflection nebula, would you see absorption lines, emission lines, or no lines? Explain your answer.

Question 11.24

24. Why is it useful to plot the apparent magnitudes of stars in a single cluster on an H-R diagram?

Question 11.25

25. What might happen to the massive outer planets when the Sun becomes a giant?

Question 11.26

26. Why does a shock wave from a supernova produce relatively few high-mass O and B stars compared to the number of low-mass A, F, G, K, and M stars produced?

Question 11.27

27. How would you distinguish a newly formed protostar from a giant, given that they occupy the same location on the H-R diagram?

Question 11.28

28. What observational consequences would we find in H-R diagrams for star clusters as a result of the universe having a finite age? Could we use these consequences to establish constraints on the possible age of the universe? Explain your answers.

Discussion Questions

Question 11.29

29. Discuss the possibility of life-forms and biological processes occurring in giant molecular clouds. In what ways might conditions favor or hinder biological evolution?

Question 11.30

30. Is there any evidence that Earth has ever passed through a star-forming region in space?

Got It?

Question 11.31

31. Which “last” longer, high-mass or low-mass stars? Explain your reasoning.

Question 11.32

32. Is Jupiter a “failed” star? Why or why not?

Question 11.33

33. Which of the two stars, if either, is at the center of a binary star system? Explain your reasoning.

Question 11.34

34. Did the Sun form shortly after the universe came into existence? Explain your answer.

Question 11.35

35. Are stars still forming today? Explain your answer.