Questions for Chapter 16
1. What is this?
2. What are the constituents of the interstellar medium? What is its chemical composition and how do we measure it?
3. What is a molecular cloud? How do a molecular cloud's temperature and density compare with the rest of the interstellar medium?
4. What is interstellar dust? How does it interact with visible light? What are the consequences for our view of the heavens, and how is that view different in infrared light?
5. Describe how our view of the night sky would be different if there were no dust grains in the interstellar medium.
6. What features of molecular clouds make the conditions favorable for star formation? Why?
7. Why do stars tend to form in clusters? Describe the process by which a single cloud gives birth to an entire cluster of stars.
8. Suppose pressure and gravity are perfectly balanced within a certain molecular cloud. Describe what would happen to that balance if the temperature suddenly dropped. What would happen if the temperature suddenly rose? What would happen if the density suddenly increased without a change in temperature? What would happen if the cloud gained a little bit of mass?
9. Why do we think the very first stars were much more massive than the Sun?
10. What happens to a contracting cloud when its thermal energy can no longer escape the cloud's interior in the form of photons? How does the trapped thermal energy affect the process of star formation?
11. What is a protostar? How does it form? Why does its mass increase with time?
12. What is a protostellar disk? Describe how these disks enable additional matter to accrete onto the protostar.
13. What are protostellar jets? Why do we think they are related to the protostar's rotation? How do they affect the cloud surrounding the protostar?
14. Why does radiation of thermal energy from the surface of a protostar enable its central temperature to rise?
15. Describe the final stages a protostar goes through before fusion begins in its core. How are these stages represented on a life track?
16. Describe the life history of a protostar from its beginning as part of a molecular cloud to the moment hydrogen fusion begins. Give as many details as possible. How would that life story be different if the protostar formed in a cloud without any angular momentum?
17. Why do more massive protostars evolve onto the Main Sequence faster?
18. What is degeneracy pressure, and how does it differ from thermal pressure? Explain why degeneracy pressure can support a stellar core against gravity even when the core becomes very cold.
19. What is the minimum mass for a star, and why can't objects with lower masses be true stars? What is a brown dwarf?
20. How are brown dwarfs like jovian planets? In what ways are brown dwarfs like stars?
21. What is the maximum mass of a star? What kind of pressure limits how massive a star can be?
22. Suppose a new star cluster is born with one O star, 10 A stars, 100 G stars, and 1000 M stars. Which stellar type dominates the light output from the cluster? What would the color of this star cluster appear to be if you observed it from a distance so great that you could not make out the individual stars?
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.
23. If you want to get a more accurate count of the number of stars in our galaxy, use an infrared telescope to observe them instead of a visible-light telescope,
24. The current mass of any star is the same as the mass it had when it first became a protostar.
25. Some of the stars in a star cluster live their entire lives and then die off before many of the cluster's stars initiate fusion.
26. Protostars are generally best observed in ultraviolet light because their surfaces have to get very hot before fusion can begin.
27. Degeneracy pressure exists only in objects that are very cold.
28. Most of the stars that formed from the same cloud as the Sun have already died off.