Question 14.1

Which property, if any, of normal matter ceases to exist in a black hole?

• a. mass
• b. chemical composition
• c. angular momentum
• d. electric charge
• e. All of these properties exist in a black hole.

Question 14.2

Supermassive black holes are found in which of the following locations?

• a. in the centers of galaxies
• b. in globular clusters
• c. in open (or galactic) clusters
• d. between galaxies
• e. in orbit with a single star

Question 14.3

Which feature is found with Kerr black holes but not Schwarzschild black holes?

• a. a singularity
• b. an event horizon
• c. gravitational redshift of photons outside of the black hole
• d. an ergoregion
• e. warping of nearby spacetime

Question 14.4

Under what conditions do all outward pressures on a collapsing star fail to stop its inward motion?

Question 14.5

In what way is a black hole blacker than black ink or a black piece of paper?

Question 14.6

If the Sun suddenly became a black hole, how would Earth’s orbit be affected?

Question 14.7

What is cosmic censorship?

Question 14.8

What are the differences between rotating and non-rotating black holes?

Question 14.9

Why are all of the observed stellar-remnant black-hole candidates members of close binary systems?

Question 14.10

If light cannot escape from a black hole, how can we detect X-rays from such an object?

Question 14.11

* What is the Schwarzschild radius of a black hole, measured in kilometers, containing 3 M_⊙? 30 M_⊙?

Question 14.12

If more massive stars evolve and die before less massive ones, why do some black-hole candidates have lower masses than their stellar companions?

Question 14.13

Under what circumstances might a neutron star in a binary star system become a black hole?

Question 14.14

Which type of black hole, nonrotating or rotating, do science fiction writers use (implicitly) in sending spaceships from one place to another through the hole? Why would the other type not be suitable?

Question 14.15

* You are standing in a train car at rest in the station, as in Figure 14-2. You measure the car’s length to be 10 m long. The train speeds up to the considerable speed of 0.95c with you still inside the car. How long will you measure the car to be now? Explain how you got your answer.

Question 14.16

A black hole of 5 M_⊙ passed by Earth at, say, Neptune’s distance from the Sun? What would happen to our planet’s orbit and to life here? Hint: The Sun’s gravitational force is about 180 times greater than the maximum effect that black hole would have on us. The Sun’s gravitational force on Earth is about 17,000 times stronger than Jupiter’s gravitational force on us, for comparison.

Question 14.17

A primordial black hole with the mass of our Moon approached, passed through, and exited Earth? What might happen to our planet and to life here? Hints: You may want to calculate the black hole’s Schwarzschild radius. Also, specify whether this is a “high-speed” or “low-speed” event.

Question 14.18

A primordial black hole exploded nearby? What would astronomers observe?

Question 14.19

To test your understanding of black hole structure, do Interactive Exercise 14.1 on the assigned Web site. You can print out your answers, if required.

Question 14.20

Search the Web for information about the stellar-mass black-hole candidate named V4641 Sgr. In what ways does it resemble other black-hole candidates, such as Cygnus X-1 and V404 Cygni? In what ways is it different and more dramatic? How do astronomers currently explain why V4641 Sgr is different?

Question 14.21

Are black holes completely black (that is, emitting or scattering no light) and are they holes (in the sense of being completely empty)? Explain.

Question 14.22

How does the mass of a young black hole compare to the mass of the neutron star from which it just formed?

Question 14.23

Are black holes giant vacuum cleaners in space that are eventually going to suck up everything in the universe? Explain your reasoning.

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Question 14.24

Which of the following most accurately describes the fate of a black hole?

• a. It will remain unchanged as long as the universe exists.
• b. It will eventually suck in everything else in the universe.
• c. It will evaporate.
• d. It will eventually start shining due to fusion in its core.
• e. It will eventually start pulsating by periodically growing larger and then smaller.

Question 14.25

Use the Starry Night™ program to investigate the X-ray source and probable black hole Cygnus X-1. This region of space is one of the brightest in the sky at X-ray wavelengths. Click the Home button in the toolbar and then use the Find pane to center the field of view on Cygnus X-1. If Cygnus X-1 is below the horizon, allow the program to reset the time to when it can best be seen. Click the checkbox to the left of the listing for Cygnus X-1 to apply a label to this object. Use the Zoom controls to set the field of view to 100 degrees. (a) Use the time controls in the toolbar to determine when Cygnus X-1 rises and sets on today’s date from your location. (b) Zoom in until you can see an object at the location indicated by the label. What apparent magnitude and radius does Starry Night™ give for this object (you can obtain this information from the HUD or by using the Show Info command from the contextual menu for this object)? Keeping in mind that the object that gives rise to this X-ray source is a black hole, to what must this apparent magnitude and radius refer? Explain.