Question 1

Which of the following relativistic effects is measured when gravitational waves are observed?

Accepted Answer

A) change in time 
B) change in length 
C) change in mass 
D) change in energy 
A) change in time 
B) change in length 
C) change in mass 
D) change in energy

Question 2

The x-ray source Cygnus X-1 is a black hole candidate located in a binary star system. The x-ray source is believed to occupy a volume smaller than Earth. This size is deduced from:

Accepted Answer

A) its luminosity and spectral class. 
B) the shortness of its orbital period. 
C) the short time period of the rapid flickering in its x-ray brightness. 
D) its distance from Earth and the angle it subtends in the sky. 
A) its luminosity and spectral class. 
B) the shortness of its orbital period. 
C) the short time period of the rapid flickering in its x-ray brightness. 
D) its distance from Earth and the angle it subtends in the sky.

Question 3

What was Gravity Probe B designed to measure?

Accepted Answer

A) the speed of light 
B) the curvature of spacetime around Earth 
C) the precession of the perihelion of Mercury 
D) the slowing of time in a gravitational field 
A) the speed of light 
B) the curvature of spacetime around Earth 
C) the precession of the perihelion of Mercury 
D) the slowing of time in a gravitational field

Question 4

Spectral lines detected from the surfaces of white dwarf stars are slightly redshifted with respect to the equivalent spectral absorption lines in the laboratory. Why is this?

Accepted Answer

A) The rapid rotation of these stars produces a redshift of light from atoms on their surfaces. 
B) The extremely high temperature of the star surface affects the atomic energy levels and therefore the spectral lines produced by the atoms. 
C) The steady shrinkage of white dwarf stars as they evolve is reflected in Doppler redshift of the surface spectrum. 
D) Photons are gravitationally redshifted by the intense gravity field of the star. 
A) The rapid rotation of these stars produces a redshift of light from atoms on their surfaces. 
B) The extremely high temperature of the star surface affects the atomic energy levels and therefore the spectral lines produced by the atoms. 
C) The steady shrinkage of white dwarf stars as they evolve is reflected in Doppler redshift of the surface spectrum. 
D) Photons are gravitationally redshifted by the intense gravity field of the star.

Question 5

A black hole is believed to form:

Accepted Answer

A) when two solar mass stars collide. 
B) by the condensation of a dust cloud that is too cold to form a star. 
C) by the gravitational collapse of a planetary nebula. 
D) at the end of the evolution of a very massive star. 
A) when two solar mass stars collide. 
B) by the condensation of a dust cloud that is too cold to form a star. 
C) by the gravitational collapse of a planetary nebula. 
D) at the end of the evolution of a very massive star.

Question 6

How are large amounts of heavy elements, such as gold, silver, and uranium, known to be formed?

Accepted Answer

A) in the nova explosion on the surface of a white dwarf star 
B) in the explosion that occurs on the surface of a neutron star 
C) in the merger of two neutron stars 
D) when a white dwarf star merges with a neutron star 
A) in the nova explosion on the surface of a white dwarf star 
B) in the explosion that occurs on the surface of a neutron star 
C) in the merger of two neutron stars 
D) when a white dwarf star merges with a neutron star

Question 7

Who first predicted the existence of gravitational waves?

Accepted Answer

A) Isaac Newton, in 1710 
B) Albert Einstein, in 1915 
C) Edwin Hubble, in 1924 
D) Stephen Hawking, in 1984 
A) Isaac Newton, in 1710 
B) Albert Einstein, in 1915 
C) Edwin Hubble, in 1924 
D) Stephen Hawking, in 1984

Question 8

A flickering signal is received from a source the size of the Sun. What frequencies are possible for this flicker?

Accepted Answer

A) any frequency at all depending on the source mechanism 
B) 0.21 cycles per second or more 
C) 0.21 cycles per second or less 
D) 0.42 cycles per second or more 
A) any frequency at all depending on the source mechanism 
B) 0.21 cycles per second or more 
C) 0.21 cycles per second or less 
D) 0.42 cycles per second or more

Question 9

A person is standing beside the open doorway of an empty barn. A pole of the same length as the barn is lying on the ground outside the barn. A second person picks up the pole and runs toward the barn at 90% of the speed of light, with the pole pointing toward the barn (a very athletic person!). How long does the pole appear to be to the person standing by the door, compared to the barn?

Accepted Answer

A) 19% of the length of the barn 
B) 90% of the length of the barn 
C) 44% of the length of the barn 
D) 81% of the length of the barn 
A) 19% of the length of the barn 
B) 90% of the length of the barn 
C) 44% of the length of the barn 
D) 81% of the length of the barn

Question 10

What is the relationship between the size of black hole and its density?

Accepted Answer

A) Larger black holes have greater densities than smaller black holes. 
B) Smaller black holes have greater densities than larger black holes. 
C) All black holes have approximately the same density. 
D) There is no relationship between size and density of a black hole. 
A) Larger black holes have greater densities than smaller black holes. 
B) Smaller black holes have greater densities than larger black holes. 
C) All black holes have approximately the same density. 
D) There is no relationship between size and density of a black hole.

Question 11

A cube falls into a black hole with one flat side aimed directly for the hole. What happens to the dimensions of the cube?

Accepted Answer

A) Length, width, and height all shrink in the same fashion, so the cube retains its shape. 
B) The dimension moving toward the hole is stretched, but the other two remain unchanged. 
C) All three dimensions are distorted as the nearer points are pulled harder toward the singularity than the further points. 
D) The dimension moving toward the hole is shortened, but the other two remain unchanged. 
A) Length, width, and height all shrink in the same fashion, so the cube retains its shape. 
B) The dimension moving toward the hole is stretched, but the other two remain unchanged. 
C) All three dimensions are distorted as the nearer points are pulled harder toward the singularity than the further points. 
D) The dimension moving toward the hole is shortened, but the other two remain unchanged.

Question 12

What is the current status of primordial black holes?

Accepted Answer

A) Primordial black holes have been created in the laboratory but never observed in nature. 
B) Primordial black holes have been observed in supernova remnants. 
C) No primordial black holes have been observed. 
D) Primordial black holes have been found virtually everywhere in the universe. 
A) Primordial black holes have been created in the laboratory but never observed in nature. 
B) Primordial black holes have been observed in supernova remnants. 
C) No primordial black holes have been observed. 
D) Primordial black holes have been found virtually everywhere in the universe.

Question 13

If you were watching a friend (or better still, an enemy!) who has fallen as far as the event horizon of a black hole, what would you measure as his heartbeat (apart from effects caused by his adrenaline level)?

Accepted Answer

A) It would appear to be normal because gravity has no effect on time intervals. 
B) It would appear to have slowed down somewhat, but not much, because of the change of the speed of light in the gravity field. 
C) It would appear to be zero; his heart would appear to have stopped. 
D) It would appear to have speeded up to an incredible rate. 
A) It would appear to be normal because gravity has no effect on time intervals. 
B) It would appear to have slowed down somewhat, but not much, because of the change of the speed of light in the gravity field. 
C) It would appear to be zero; his heart would appear to have stopped. 
D) It would appear to have speeded up to an incredible rate.

Question 14

Black holes with which of the following masses are most likely to have evaporated within the lifetime of our universe?

Accepted Answer

A) supermassive, similar to those at the centers of galaxies 
B) very low mass, about that of Mount Everest 
C) low mass, about that of Earth 
D) the mass of a star, about 5 Mε 
A) supermassive, similar to those at the centers of galaxies 
B) very low mass, about that of Mount Everest 
C) low mass, about that of Earth 
D) the mass of a star, about 5 Mε

Question 15

At what speed would an object have to be traveling for its length to appear to a stationary observer to have decreased to 1/3 of its length when seen at rest? (c = speed of light)

Accepted Answer

A) 0.11 c, or 11% of the speed of light 
B) 0.94 c, or 94% of the speed of light 
C) 0.33 c, or 1/3 c 
D) 0.89 c, or 89% of the speed of light 
A) 0.11 c, or 11% of the speed of light 
B) 0.94 c, or 94% of the speed of light 
C) 0.33 c, or 1/3 c 
D) 0.89 c, or 89% of the speed of light

Question 16

The mass of Cygnus X-1 is estimated to be 14.8 Mε. How was this determined?

Accepted Answer

A) measurement of the gravitational redshift 
B) use of Kepler's third law 
C) measurement of the Doppler shift of the binary system, of which it is a part 
D) visual measurement of the "wobble" in the binary system 
A) measurement of the gravitational redshift 
B) use of Kepler's third law 
C) measurement of the Doppler shift of the binary system, of which it is a part 
D) visual measurement of the "wobble" in the binary system

Question 17

What is believed to be the mass of the black hole candidate Cygnus X-1?

Accepted Answer

A) 30 Mε 
B) 1 billion Mε 
C) 15 Mε 
D) 1 Mε 
A) 30 Mε 
B) 1 billion Mε 
C) 15 Mε 
D) 1 Mε

Question 18

The radius of the event horizon of a black hole, the Schwarzschild radius:

Accepted Answer

A) is constant, because the general theory of relativity states that the size of a black hole is independent of its mass. 
B) is smaller the more massive the black hole, because the matter will be more condensed. 
C) will not depend on its mass but will depend on the material from which it was formed, a "hydrogen" black hole being smaller than an "iron" black hole. 
D) is larger, the more massive the black hole. 
A) is constant, because the general theory of relativity states that the size of a black hole is independent of its mass. 
B) is smaller the more massive the black hole, because the matter will be more condensed. 
C) will not depend on its mass but will depend on the material from which it was formed, a "hydrogen" black hole being smaller than an "iron" black hole. 
D) is larger, the more massive the black hole.

Question 19

Astronomers originally rejected the idea that white dwarfs could rotate fast enough to be responsible for pulsar radiation. However, they soon accepted the idea that neutron stars could produce pulsar radiation. Why this difference?

Accepted Answer

A) The earlier rejection was mistaken. With sufficient evidence astronomers have come to believe that both white dwarfs and neutron stars can produce pulsar radiation. 
B) There are two types of white dwarfs: those that produce Type Ia supernova and those that do not. The earlier rejection applied to the second type. It is now believed that the Ia supernova type white dwarfs, along with neutron stars, can produce pulsar radiation. 
C) Neutron stars are smaller and even more dense than white dwarfs. Thus, they can rotate at tremendous rates without flying apart. 
D) Neutron stars are held together by nuclear forces that are much stronger than the gravitational forces operating in white dwarfs. Thus, the surface of a neutron star can pulse in and out much more quickly than the surface of a white dwarf. 
A) The earlier rejection was mistaken. With sufficient evidence astronomers have come to believe that both white dwarfs and neutron stars can produce pulsar radiation. 
B) There are two types of white dwarfs: those that produce Type Ia supernova and those that do not. The earlier rejection applied to the second type. It is now believed that the Ia supernova type white dwarfs, along with neutron stars, can produce pulsar radiation. 
C) Neutron stars are smaller and even more dense than white dwarfs. Thus, they can rotate at tremendous rates without flying apart. 
D) Neutron stars are held together by nuclear forces that are much stronger than the gravitational forces operating in white dwarfs. Thus, the surface of a neutron star can pulse in and out much more quickly than the surface of a white dwarf.

Question 20

What is "special" about the special theory of relativity?

Accepted Answer

A) It deals only with objects that are at rest relative to one other. 
B) It deals only with objects moving in a straight line at constant speed. 
C) It deals only with motion at speeds significantly less than the speed of light. 
D) It deals with motion at constant velocity and accelerated motion but excludes all other effects; in particular, it excludes gravity. 
A) It deals only with objects that are at rest relative to one other. 
B) It deals only with objects moving in a straight line at constant speed. 
C) It deals only with motion at speeds significantly less than the speed of light. 
D) It deals with motion at constant velocity and accelerated motion but excludes all other effects; in particular, it excludes gravity.

Exam 21: Stellar Remnants: Neutron Stars and Black Holes

Which of the following relativistic effects is measured when gravitational waves are observed?

The x-ray source Cygnus X-1 is a black hole candidate located in a binary star system. The x-ray source is believed to occupy a volume smaller than Earth. This size is deduced from:

What was Gravity Probe B designed to measure?

Spectral lines detected from the surfaces of white dwarf stars are slightly redshifted with respect to the equivalent spectral absorption lines in the laboratory. Why is this?

A black hole is believed to form:

How are large amounts of heavy elements, such as gold, silver, and uranium, known to be formed?

Who first predicted the existence of gravitational waves?

A flickering signal is received from a source the size of the Sun. What frequencies are possible for this flicker?

What is the relationship between the size of black hole and its density?

A cube falls into a black hole with one flat side aimed directly for the hole. What happens to the dimensions of the cube?

What is the current status of primordial black holes?

If you were watching a friend (or better still, an enemy!) who has fallen as far as the event horizon of a black hole, what would you measure as his heartbeat (apart from effects caused by his adrenaline level)?

Black holes with which of the following masses are most likely to have evaporated within the lifetime of our universe?

At what speed would an object have to be traveling for its length to appear to a stationary observer to have decreased to 1/3 of its length when seen at rest? (c = speed of light)

The mass of Cygnus X-1 is estimated to be 14.8 Mε. How was this determined?

What is believed to be the mass of the black hole candidate Cygnus X-1?

The radius of the event horizon of a black hole, the Schwarzschild radius:

Astronomers originally rejected the idea that white dwarfs could rotate fast enough to be responsible for pulsar radiation. However, they soon accepted the idea that neutron stars could produce pulsar radiation. Why this difference?

What is "special" about the special theory of relativity?

Astronomy and the Universe

Knowing the Heavens

Eclipses and the Motion of the Moon

Gravitation and the Waltz of the Planets

The Nature of Light

Optics and Telescopes

Comparative Planetology I: Our Solar System

Comparative Planetology II: the Origin of Our Solar System

The Living Earth

Our Barren Moon

Mercury, Venus, and Mars: Terrestrial, yet Unique

Jupiter and Saturn: Lords of the Planets

Jupiter and Saturns Satellites of Fire and Ice

Uranus, Neptune, Pluto, and the Kuiper Belt: Remote Worlds

Asteroids, Comets, and Impacts

Our Star, the Sun

The Nature of the Stars

The Birth of Stars

Stellar Evolution: on and After the Main Sequence

Stellar Evolution: The Death of Stars

Our Galaxy

Galaxies

Quasars and Active Galaxies

Cosmology: The Origin and Evolution of the Universe

Exploring the Early Universe

The Search for Extraterrestrial Life

Filters

The mass of Cygnus X-1 is estimated to be 14.8 M_ε. How was this determined?