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Exam 15: Black Holes: Matters of Gravity

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Question 81

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If Alice stays on Earth while Bob races off in a rocket at a speed close to the speed of light, then, according to special relativity Alice will see a clock on the rocket appear to tick more slowly than the one on her wall. If Bob looks back at Alice's wall clock, then according to the same theory Bob will see the wall clock appear to tick

A) at the same speed as the clock on the rocket.
B) faster than the clock on the rocket.
C) faster or slower than the clock on the rocket, depending on the direction of travel of the rocket compared with Earth.
D) slower than the clock on the rocket.

E) A) and D)
F) B) and D)

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Question 82

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If the Sun were replaced by a 1-solar-mass black hole, then Earth would

A) enter an elliptical orbit passing close to the black hole, with its farthest distance from the black hole equal to 1 au.
B) spiral quickly into the black hole.
C) head off into interstellar space along a straight-line tangent to its original orbit around the Sun.
D) continue to orbit the black hole in its present orbit.

E) A) and C)
F) All of the above

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Question 83

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What happens to the magnetic field of a star that collapses completely to become a black hole?

Which of these measurements is the lower limit for a main-sequence star that will eventually form a black hole?

Which of these statements does NOT correctly compares gamma-ray bursts with X-ray bursts?

Gravitational waves are

The black hole at the center of the galaxy M87 is estimated to have a mass of 3 * 10⁹ M_Sun. Suppose the orbits of the stars observed circling it have semimajor axes of 50 au. Approximately what would be the period of their orbital motion?

Which of these techniques has been successful in identifying good candidates for a black hole in the Milky Way Galaxy?

Why is Cygnus X-1 thought to be a black hole?

In what way is the general theory of relativity more "general" (i.e., deals with more situations) than the special theory of relativity?

How does a gravitational field affect the passage of time?

What is it that is actually located at the event horizon of a black hole?

X-rays that come from the vicinity of a black hole actually originate from

Einstein's theory of special relativity contains some very strange ideas such as time dilation (moving clocks run slow) , length contraction (moving lengths are shorter) , and lack of absolute simultaneity. What is the basis of these ideas?

What is the Schwarzschild radius of a 2-solar-mass black hole?

What is the distance from the center to the event horizon of a nonrotating black hole with the mass of Earth?

Two spaceships are traveling past Earth at 90% of the speed of light in opposite directions (i.e., they are approaching each other) . One spaceship turns on a searchlight, which is seen by scientists aboard the other. What speed do the scientists measure for this light (c = speed of light in a vacuum) ?

A student is on Mars standing on the gangplank of a spaceship when she sees an identical spaceship go past Mars at 90% of the speed of light. When she looks closely at this spaceship, how does it compare with her own spaceship?

In the context of black holes, a singularity is a(n)

A compact body pulls material from a binary companion. This material plunges toward the compact body and emits X-rays. Which of these phenomena would this description NOT fit?