Question 1

As you are investigating a black hole from a safe distance,a rivet pops out of the tailfin on your spaceship and falls toward the black hole.Will you ever see the rivet enter the event horizon?

Accepted Answer

As the rivet approaches the event horizon, time dilation causes it to appear to slow down and never actually cross the horizon from an outside observer's perspective.

Question 2

Because of the relativistic nature of spacetime in the vicinity of a black hole,a satellite orbiting the hole in one direction would have a different orbital period from a satellite orbiting in the other direction.This fact is a violation of:

Accepted Answer

Kepler's third law states that the square of the orbital period of a planet or satellite is proportional to the cube of the semi-major axis of its orbit. The different orbital periods of satellites orbiting in opposite directions around a black hole violate this law. The other choices are not relevant to this situation because the relativistic effects on the satellite orbits do not violate the conservation of energy, the principle of equivalence, or the conservation of angular momentum.

Question 3

What is a Kerr black hole?

Accepted Answer

A Kerr black hole is a rotating black hole, named after physicist Roy Kerr who first solved the equations for this type of black hole in 1963. It is characterized by its angular momentum, which causes frame dragging and other effects on the space-time surrounding the black hole.

Question 4

A laborer repairing the clock tower on a space station orbiting a black hole accidentally drops the clock in such a way that it accelerates toward the black hole.What does the worker see while watching the clock?

Accepted Answer

The worker would observe the clock's hands moving slower and slower as it approaches the event horizon. This is due to time dilation, a phenomenon predicted by Einstein's theory of relativity, which states that time appears to slow down or speed up depending on the gravitational field strength. The closer the clock is to the black hole's strong gravitational field, the slower time appears to pass. This effect would become more pronounced as the clock approached the event horizon, the point of no return, where the gravity becomes so strong that not even light can escape. At this point, the hands of the clock would appear to stop moving to an outside observer.

Question 5

What name is given to a rotating black hole?

Accepted Answer

A rotating black hole is also known as a Kerr black hole, named after the physicist Roy Kerr who first described it in 1963. The Kerr black hole is formed from the collapse of a rotating, massive star and is characterized by its the spin parameter, which determines the strength of the black hole's rotation.

Question 6

What is located in the exact center of a Kerr (rotating)black hole?

Accepted Answer

The answer of What is located in the exact center...

Question 7

In general,how many fundamentally different types of black holes are expected to exist?

Accepted Answer

Black holes are generally categorized based on their rotation: those that rotate (Kerr black holes) and those that do not rotate (Schwarzschild black holes).

Question 8

A space freighter accidentally drops a steel beam while passing a black hole,and the beam starts falling toward the black hole with the long direction of the beam pointing toward the black hole.What happens to the beam as it approaches the event horizon?

Accepted Answer

The beam experiences spaghettification as it approaches the black hole, meaning it is stretched in length due to the intense gravitational gradient (tidal forces) while being compressed in width.

Question 9

What is the ergoregion of a Kerr black hole?

Accepted Answer

The ergoregion is a region outside the event horizon of a Kerr black hole where objects cannot remain at rest without falling into the black hole. This is due to the rotational energy of the black hole, which makes space itself rotate. Objects within the ergoregion must orbit in the same direction as the black hole's rotation, or they will be dragged along with the rotating spacetime and eventually be consumed by the black hole.

Question 10

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

Accepted Answer

The answer of What happens to the magnetic field of...

Question 11

One day,while straying dangerously close to a black hole,you notice that no matter how hard you try to remain at rest,you are inevitably drawn into the black hole unless you keep moving.What does this experience tell you about the black hole (other than that you should not be near it!)?

Accepted Answer

The experience suggests that the black hole is rotating. This is because the phenomenon described is due to the effects of the black hole's rotation on nearby space-time. The rotation of a black hole causes space-time to be dragged along with it. As a result, an object that appears to be stationary relative to the space-time around the black hole will be dragged towards it if it does not move. This effect is known as frame dragging.

Question 12

Where does the energy come from to produce the gravitational waves that are emitted when a massive star collapses to become a black hole?

Accepted Answer

The answer of Where does the energy come from to...

Question 13

What would happen to the gravitational force on Earth if the Sun were to be replaced by a 1-solar-mass black hole?

Accepted Answer

The gravitational force on Earth would remain as it is now. This is because the strength of the gravitational force between two objects depends only on their masses and the distance between them, not on the nature of the objects. Therefore, if the Sun were to be replaced by a black hole of the same mass, the gravitational force on Earth would remain the same.

Question 14

Black holes do not possess a magnetic field because:

Accepted Answer

The answer of Black holes do not possess a magnetic...

Question 15

How do Kerr black holes differ from Schwarzschild black holes?

Accepted Answer

Kerr black holes rotate, while Schwarzschild black holes do not. This rotation creates a different spacetime geometry, with a region called the ergosphere outside the event horizon where objects can be dragged along with the black hole's rotation, and a ring singularity instead of a point singularity at the center.

Question 16

The difference between a Schwarzschild black hole (SBH)and a Kerr black hole (KBH)is:

Accepted Answer

The main difference between a Schwarzschild black hole and a Kerr black hole is that the Kerr black hole is spinning, whereas the Schwarzschild black hole is not. The overall mass can vary for both types of black holes, and while Kerr black holes can have electric charge, this is not the main distinguishing feature between the two types.

Question 17

What is a Schwarzschild black hole?

Accepted Answer

A Schwarzschild black hole is a nonrotating black hole that is characterized by its event horizon, which is also called the Schwarzschild radius. It is named after the German physicist Karl Schwarzschild, who first solved Einstein's field equations to describe the gravity of a nonrotating black hole. The Schwarzschild radius is the radius at which the escape velocity equals the speed of light, which means that anything that passes inside this radius is trapped by the black hole's gravity and cannot escape, including light.

Question 18

What name is given to a nonrotating black hole?

Accepted Answer

A nonrotating black hole is also known as a Schwarzschild black hole, named after the German physicist Karl Schwarzschild who first derived the mathematical solution describing a nonrotating black hole.

Question 19

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

Accepted Answer

The gravitational pull of a 1-solar-mass black hole would be the same as that of the Sun, so Earth would continue in its current orbit.

Question 20

In the context of black holes,the word ergosphere names the:

Accepted Answer

The ergosphere is a region just outside the event horizon of a rotating black hole where it is impossible for anything to remain at rest. This is due to the strong gravitational effects of the black hole causing space to become twisted and dragged along with the rotation of the black hole. As a result, even light cannot remain stationary in this region.

Quiz 12: The Deaths and Remnants of Stars