Questions for Chapter 18

1. What is this?

2. What is degeneracy pressure, and how is it important to the existence of white dwarfs and neutron stars? What is the difference between electron degeneracy pressure and neutron degeneracy pressure?

3. Describe the mass, size, and density of a typical white dwarf. How does the size of a white dwarf depend on its mass?

4. What is the white dwarf limit?

5. What are accretion disks, and why do we find them only in close binary systems? Explain how the accretion disk provides a white dwarf with a new source of energy that we can detect from Earth.

6. What is a nova? Describe the process that creates a nova, and what a nova looks like.

7. What causes a white dwarf supernova? Observationally, how do we distinguish white dwarf and massive star supernovae?

8. What is this? [This is an x-ray movie]

9. Describe the mass, size, and density of a typical neutron star.

10. How do we know that pulsars are neutron stars? Are all neutron stars also pulsars? Explain.

11. Explain how the presence of a neutron star can make a close binary star system appear to us as an X-ray binary. Why do some of these systems appear to us as X-ray bursters?

12. . The X-ray bursts that happen on the surface of an accreting neutron star are not powerful enough to accelerate the exploding material to escape velocity. Predict what will happen in an X-ray binary system in which the companion star eventually feeds more than 3 solar masses of matter into the neutron star's accretion disk.

13. What do we mean when we say that a black hole is like a hole in spacetime? What is the event horizon of a black hole, and how is it related to the Schwarzschild radius? What are the three measurable properties of a black hole?

14. Explain why the principle of conservation of energy makes it very difficult to fall into a black hole.

15. Suppose you are falling into a black hole. How will you perceive the passage of your own time? How will you perceive the passage of time in the universe around you? Briefly explain why your trip is likely to be lethal.

16. Why do we think that supernovae should sometimes form black holes? What observational evidence supports the existence of black holes?

17. Which kind of object do you think is most common in our galaxy: white dwarfs, neutron stars, or black holes? Explain your reasoning.

18. Summarize current ideas about the causes of gamma-ray bursts.

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.

19. The white dwarf at the center of the Helix Nebula has a mass three times the mass of our Sun.

20. The radii of white dwarf stars in close binary systems gradually increase as they accrete matter.

21. If you want to find a pulsar, you should look near the remnant of a supernova described by ancient Chinese astronomers.

22. It's the year 2020, and scientists have just learned that there is a 10-solar-mass black hole lurking near Pluto's orbit.

23. If the Sun suddenly became a l M_sun black hole, the orbits of the planets would not change at all.

24. We can detect black holes with X-ray telescopes because matter falling into a black hole emits X rays after it smashes into the event horizon.

25. The merger of two black holes forms a black hole with a smaller Schwarzschild radius than the original black holes.

26. If the Sun suddenly became a 1 M_sun black hole, Earth's tides would become much greater.

27. The pulsation period of a pulsar appears to speed up if the pulsar is moving toward us.