Question 1

A black hole is so named because

Accepted Answer

Black holes are named for their property that no light or other forms of electromagnetic radiation can escape from them, making them appear black. This is due to their extremely strong gravitational pull.

Question 2

In a binary star system, an unseen component is found to have 8 solar masses. It would be visible if the system were a normal star, so it must be a collapsed object. Theoretical considerations declare that it must be a

Accepted Answer

A black hole is the correct answer because an object with 8 solar masses is too massive to be a neutron star or a white dwarf, both of which have maximum mass limits below this value. Brown dwarfs are also not collapsed objects in the context of being remnants of stellar evolution.

Question 3

What happens to a photon that leaves the interior of a black hole aimed directly upward (radially outward)?

Accepted Answer

The answer of What happens to a photon that leaves...

Question 4

Which of these statements is NOT an observation confirming the predictions of general relativity?

Accepted Answer

Primordial black holes have not been directly detected; their existence is a theoretical prediction that could provide insights into both general relativity and cosmology, but as of my last update, there has been no direct observational confirmation of their existence. Choices A, B, and D are classic observations that confirm predictions of general relativity.

Question 5

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

Accepted Answer

The lower limit for a main-sequence star to eventually form a black hole is generally considered to be around 25 solar masses. Stars with this mass or greater can undergo a supernova explosion and leave behind a black hole.

Question 6

A photon is emitted from the surface of a massive star. Which of these will the photon NOT experience as it moves away from the star?

Accepted Answer

Photons always travel at the speed of light in a vacuum, which is constant and does not change due to gravity. The effects of gravity on a photon escaping a massive star include redshift (increased wavelength) and reduced energy, but the speed remains constant.

Question 7

What is a singularity?

Accepted Answer

A singularity, in the context of black holes, refers to a point of infinite density where the gravitational pull is so strong that not even light can escape. This is where the laws of physics as we know them break down.

Question 8

A black hole is so named because

Accepted Answer

Black holes are named for their characteristic of not allowing any light to escape once it passes the event horizon, due to their extremely strong gravitational fields. This means they do not emit any light, making them "black."

Question 9

The escape velocity of matter from the center of a black hole greater than 3 solar masses is

Accepted Answer

The escape velocity from the center of a black hole is greater than the speed of light. This is why not even light can escape from a black hole, leading to its characteristic darkness.

Question 10

What physical theory has been developed to describe adequately the details of what happens inside a black hole?

Accepted Answer

Currently, there is no physical theory that adequately describes the details of what happens inside a black hole. General relativity breaks down at the singularity, and quantum theory does not fully reconcile with general relativity in these extreme conditions.

Question 11

The escape velocity for material inside a black hole is

Accepted Answer

The escape velocity for material inside a black hole is greater than the speed of light, meaning nothing, not even light, can escape once it crosses the event horizon.

Question 12

What is the likely final fate of a star of 30 solar masses when it is on the main sequence?

Accepted Answer

Stars of 30 solar masses are massive enough that, after exhausting their nuclear fuel, they will likely collapse under their own gravity and become black holes.

Question 13

One feature that distinguishes a black hole from all other objects in the universe is that

Accepted Answer

The defining feature of a black hole is that its escape velocity exceeds the speed of light, meaning nothing, not even light, can escape from inside it. This is what distinguishes black holes from other objects in the universe.

Question 14

A black hole can be thought of as

Accepted Answer

A black hole is a region in space where the gravitational pull is so strong that nothing, not even light (electromagnetic radiation), can escape from it. This is due to its extremely high mass density.

Question 15

In a binary star system, one component is found to have about 3 solar masses, the other about 7 solar masses. The 3-solar-mass star is visible from Earth, but the 7-solar-mass star is not. Theoretical considerations declare that the 7-solar-mass star must be a

Accepted Answer

A 7-solar-mass star not visible from Earth in a binary system, given its mass, is most likely a black hole. Stars with such mass that have ended their life cycle would have undergone supernova explosions, leaving behind dense remnants. Given the mass, it's too heavy to be a neutron star (typically up to about 2.5 solar masses) or a white dwarf (up to about 1.4 solar masses, the Chandrasekhar limit). A cool planetary object wouldn't have such a high mass. Thus, a black hole is the most plausible option, as it is an end state for massive stars and would not emit light, making it invisible from Earth.

Question 16

What is believed to be the maximum mass for a neutron star?

Accepted Answer

The maximum mass for a neutron star is believed to be around 3 solar masses. Beyond this limit, it is thought that the gravitational pull becomes so strong that it would lead to the formation of a black hole. This limit is often referred to as the Tolman–Oppenheimer–Volkoff limit.

Question 17

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

Accepted Answer

A singularity in the context of black holes refers to a point where a nonzero mass occupies zero volume, leading to an infinite density. This is a theoretical point within a black hole where the laws of physics as we understand them break down.

Question 18

Which of these is NOT a test of general relativity but rather a test of special relativity?

Accepted Answer

Tests of special relativity focus on phenomena that occur due to relative motion in the absence of gravitational effects. The length contraction (A) is a direct consequence of special relativity, which deals with the effects observed between different inertial frames moving at constant velocities relative to each other, without involving gravity.

Question 19

Suppose that a neutron star of 2.9 solar masses is part of a binary star system in which the other star is a normal giant star. What would happen if 1 solar mass of material were transferred onto the neutron star from its companion?

Accepted Answer

When the mass of a neutron star exceeds the Tolman-Oppenheimer-Volkoff limit, which is about 2 to 3 solar masses, it can no longer support itself against gravitational collapse, leading to the formation of a black hole. Adding 1 solar mass to a 2.9 solar mass neutron star would push its mass well beyond this limit, resulting in its collapse into a black hole.

Question 20

Light leaving the surface of a neutron star is strongly redshifted. What name is given to this effect?

Accepted Answer

Gravitational redshift occurs because the intense gravity of a neutron star significantly warps spacetime, causing light escaping its surface to lose energy and shift to the red end of the spectrum.

Quiz 15: Black Holes: Matters of Gravity

A black hole is so named because

In a binary star system, an unseen component is found to have 8 solar masses. It would be visible if the system were a normal star, so it must be a collapsed object. Theoretical considerations declare that it must be a

What happens to a photon that leaves the interior of a black hole aimed directly upward (radially outward) ?

Which of these statements is NOT an observation confirming the predictions of general relativity?

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

A photon is emitted from the surface of a massive star. Which of these will the photon NOT experience as it moves away from the star?

What is a singularity?

A black hole is so named because

The escape velocity of matter from the center of a black hole greater than 3 solar masses is

What physical theory has been developed to describe adequately the details of what happens inside a black hole?

The escape velocity for material inside a black hole is

What is the likely final fate of a star of 30 solar masses when it is on the main sequence?

One feature that distinguishes a black hole from all other objects in the universe is that

A black hole can be thought of as

In a binary star system, one component is found to have about 3 solar masses, the other about 7 solar masses. The 3-solar-mass star is visible from Earth, but the 7-solar-mass star is not. Theoretical considerations declare that the 7-solar-mass star must be a

What is believed to be the maximum mass for a neutron star?

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

Which of these is NOT a test of general relativity but rather a test of special relativity?

Suppose that a neutron star of 2.9 solar masses is part of a binary star system in which the other star is a normal giant star. What would happen if 1 solar mass of material were transferred onto the neutron star from its companion?

Light leaving the surface of a neutron star is strongly redshifted. What name is given to this effect?