Question 1

Black holes,by definition,cannot be observed directly.What observational evidence do scientists have of their existence?

Accepted Answer

A) Theoretical models predict their existence. 
B) Gravitational interaction with other objects. 
C) Space is,overall,very black. 
D) We have sent spacecraft to nearby black holes. 
E) We have detected neutrinos from them. 
A) Theoretical models predict their existence. 
B) Gravitational interaction with other objects. 
C) Space is,overall,very black. 
D) We have sent spacecraft to nearby black holes. 
E) We have detected neutrinos from them. B

Question 2

Through a bizarre (and scientifically unexplainable)fluctuation in the spacetime continuum,a copy of a book titled Iguoonos: How We Evolved appears on your desk.As you begin to read,you learn that the book describes the evolution of the people living in the star system described above.In the first chapter,you learn that these people evolved from organisms that lived 5 billion years ago.Which of the following statements should you expect to find as you continue to read this book?

Accepted Answer

A) As a result of traumatic experiences of their evolutionary ancestors,they dislike television. 
B) Their immediate ancestors were chimpanzees. 
C) They found that the presence of two stars in their system was critical to their evolution. 
D) They evolved on a different planet in a different star system and moved to their current location. 
E) They evolved from primitive wormlike creatures that had 13 legs,4 eyes,and bald heads,thus explaining why such critters are now considered a spectacular delicacy. 
A) As a result of traumatic experiences of their evolutionary ancestors,they dislike television. 
B) Their immediate ancestors were chimpanzees. 
C) They found that the presence of two stars in their system was critical to their evolution. 
D) They evolved on a different planet in a different star system and moved to their current location. 
E) They evolved from primitive wormlike creatures that had 13 legs,4 eyes,and bald heads,thus explaining why such critters are now considered a spectacular delicacy. D

Question 3

What do we mean by the event horizon of a black hole?

Accepted Answer

A) It is the very center of the black hole. 
B) It is the distance from the black hole at which stable orbits are possible. 
C) It is the place where X-rays are emitted from black holes. 
D) It is the point beyond which neither light nor anything else can escape. 
A) It is the very center of the black hole. 
B) It is the distance from the black hole at which stable orbits are possible. 
C) It is the place where X-rays are emitted from black holes. 
D) It is the point beyond which neither light nor anything else can escape. D

Question 4

Neutron stars are the densest objects that we can observe in the universe.

Accepted Answer

A) True 
 B)False

Question 5

The total energy released during a neutron star merger can be even greater than that of a massive star supernova.

Accepted Answer

A) True 
 B)False

Question 6

What do we mean by the singularity of a black hole?

Accepted Answer

A) There are no binary black holes-each one is isolated. 
B) An object can become a black hole only once,and a black hole cannot evolve into anything else. 
C) It is the center of the black hole,a place of infinite density where the known laws of physics cannot describe the conditions. 
D) It is the edge of the black hole,where one could leave the observable universe. 
E) It is the "point of no return" of the black hole;anything closer than this point will not be able to escape the gravitational force of the black hole. 
A) There are no binary black holes-each one is isolated. 
B) An object can become a black hole only once,and a black hole cannot evolve into anything else. 
C) It is the center of the black hole,a place of infinite density where the known laws of physics cannot describe the conditions. 
D) It is the edge of the black hole,where one could leave the observable universe. 
E) It is the "point of no return" of the black hole;anything closer than this point will not be able to escape the gravitational force of the black hole.

Question 7

One foolhardy day,a daring major (let's call him Tom)in the space force decides to become the first of his race to cross the event horizon of the black hole.To add to the drama,he decides to go in wearing only a thin space suit,which offers no shielding against radiation,no cushioning against any forces,and so on.Which of the following is most likely to kill him first (or at least cause significant damage)? (Hint: The key word here is first.Be sure to consider the distances from the black hole at which each of the noted effects is likely to become damaging. )

Accepted Answer

A) the crush of gravity at the singularity embedded within the black hole 
B) the tidal forces due to the black hole 
C) the strong acceleration as he descends towards the black hole 
D) the X-rays from the accretion disk 
E) the sucking force from the black hole,which will cause his head to explode 
A) the crush of gravity at the singularity embedded within the black hole 
B) the tidal forces due to the black hole 
C) the strong acceleration as he descends towards the black hole 
D) the X-rays from the accretion disk 
E) the sucking force from the black hole,which will cause his head to explode

Question 8

From a theoretical standpoint,what is a pulsar?

Accepted Answer

A) a star that alternately expands and contracts in size 
B) a rapidly rotating neutron star 
C) a neutron star or black hole that happens to be in a binary system 
D) a binary system that happens to be aligned so that one star periodically eclipses the other 
E) a star that is burning iron in its core 
A) a star that alternately expands and contracts in size 
B) a rapidly rotating neutron star 
C) a neutron star or black hole that happens to be in a binary system 
D) a binary system that happens to be aligned so that one star periodically eclipses the other 
E) a star that is burning iron in its core

Question 9

Scientists have detected thousands of gamma ray bursts.The evidence suggests that most or all of these bursts

Accepted Answer

A) have occurred in the central regions of the Milky Way. 
B) have occurred in distant galaxies. 
C) come from the same types of close binary systems that produce X-ray bursts. 
D) come from the Oort cloud surrounding the Sun. 
A) have occurred in the central regions of the Milky Way. 
B) have occurred in distant galaxies. 
C) come from the same types of close binary systems that produce X-ray bursts. 
D) come from the Oort cloud surrounding the Sun.

Question 10

Why is there an upper limit to the mass of a white dwarf?

Accepted Answer

A) White dwarfs come only from stars smaller than 1.4 solar masses. 
B) The more massive the white dwarf,the greater the degeneracy pressure and the faster the speeds of its electrons.Near 1.4 solar masses,the speeds of the electrons approach the speed of light,so more mass cannot be added without breaking the degeneracy pressure. 
C) The more massive the white dwarf,the higher its temperature and hence the greater its degeneracy pressure.At about 1.4 solar masses,the temperature becomes so high that all matter effectively melts,even individual subatomic particles. 
D) The upper limit to the masses of white dwarfs was determined through observations of white dwarfs,but no one knows why the limit exists. 
E) Above this mass,the electrons would be pushed together so closely they would turn into neutrons and the star would become a neutron star. 
A) White dwarfs come only from stars smaller than 1.4 solar masses. 
B) The more massive the white dwarf,the greater the degeneracy pressure and the faster the speeds of its electrons.Near 1.4 solar masses,the speeds of the electrons approach the speed of light,so more mass cannot be added without breaking the degeneracy pressure. 
C) The more massive the white dwarf,the higher its temperature and hence the greater its degeneracy pressure.At about 1.4 solar masses,the temperature becomes so high that all matter effectively melts,even individual subatomic particles. 
D) The upper limit to the masses of white dwarfs was determined through observations of white dwarfs,but no one knows why the limit exists. 
E) Above this mass,the electrons would be pushed together so closely they would turn into neutrons and the star would become a neutron star.

Question 11

If you were to come back to our Solar System in 6 billion years,what might you expect to find?

Accepted Answer

A) a red giant star 
B) a white dwarf 
C) a rapidly spinning pulsar 
D) a black hole 
E) Everything will be pretty much the same as it is now. 
A) a red giant star 
B) a white dwarf 
C) a rapidly spinning pulsar 
D) a black hole 
E) Everything will be pretty much the same as it is now.

Question 12

What is an X-ray burster? What causes the X-ray bursts?

Accepted Answer

It is a neutron star in a clos

Question 13

Each Voyager spacecraft carries a "postcard" designed to be understandable to any aliens that might someday encounter it.On the "postcard," scientists pinpointed the location of Earth by triangulating it between pulsars.Why did the scientists choose pulsars rather than some other type of star?

Accepted Answer

A) Pulsars are very bright and therefore easy to find. 
B) Several pulsars are located within a dozen light-years of our solar system,making them useful for finding our solar system. 
C) We're pretty sure that aliens will have only radio telescopes and not optical telescopes,so they'll have a better chance of seeing pulsars than ordinary stars. 
D) Pulsars are easy to identify by their almost perfectly steady periods of pulsation. 
A) Pulsars are very bright and therefore easy to find. 
B) Several pulsars are located within a dozen light-years of our solar system,making them useful for finding our solar system. 
C) We're pretty sure that aliens will have only radio telescopes and not optical telescopes,so they'll have a better chance of seeing pulsars than ordinary stars. 
D) Pulsars are easy to identify by their almost perfectly steady periods of pulsation.

Question 14

Which of the following best describes why a white dwarf cannot have a mass greater than the 1.4-solar-mass limit?

Accepted Answer

A) Electron degeneracy pressure depends on the speeds of electrons,which approach the speed of light as a white dwarf's mass approaches the 1.4-solar-mass limit. 
B) White dwarfs get hotter with increasing mass,and above the 1.4-solar-mass limit they would be so hot that even their electrons would melt. 
C) White dwarfs are made only from stars that have masses less than the 1.4-solar-mass limit. 
D) The upper limit to a white dwarf's mass is something we have learned from observations,but no one knows why this limit exists. 
A) Electron degeneracy pressure depends on the speeds of electrons,which approach the speed of light as a white dwarf's mass approaches the 1.4-solar-mass limit. 
B) White dwarfs get hotter with increasing mass,and above the 1.4-solar-mass limit they would be so hot that even their electrons would melt. 
C) White dwarfs are made only from stars that have masses less than the 1.4-solar-mass limit. 
D) The upper limit to a white dwarf's mass is something we have learned from observations,but no one knows why this limit exists.

Question 15

How do we know that pulsars are neutron stars?

Accepted Answer

A) We have observed massive-star supernovae produce pulsars. 
B) Pulsars and neutron stars look exactly the same. 
C) No massive object,other than a neutron star,could spin as fast as we observe pulsars spin. 
D) Pulsars have the same upper mass limit as neutron stars do. 
E) none of the above 
A) We have observed massive-star supernovae produce pulsars. 
B) Pulsars and neutron stars look exactly the same. 
C) No massive object,other than a neutron star,could spin as fast as we observe pulsars spin. 
D) Pulsars have the same upper mass limit as neutron stars do. 
E) none of the above

Question 16

Which of the following is not true about differences between novae and supernovae?

Accepted Answer

A) Novae are much less luminous than supernovae. 
B) Supernovae eject gas into space but novae do not. 
C) Novae occur only in binary star systems,while supernovae can occur both among single stars and among binary star systems. 
D) The same star can undergo novae explosions more than once,but can undergo only a single supernova. 
A) Novae are much less luminous than supernovae. 
B) Supernovae eject gas into space but novae do not. 
C) Novae occur only in binary star systems,while supernovae can occur both among single stars and among binary star systems. 
D) The same star can undergo novae explosions more than once,but can undergo only a single supernova.

Question 17

What do we mean by the singularity of a black hole?

Accepted Answer

A) It is the center of the black hole,a place of infinite density where the known laws of physics cannot describe the conditions. 
B) It is the "point of no return" of the black hole;anything closer than this point will not be able to escape the gravitational force of the black hole. 
C) It is the edge of the black hole,where one could leave the observable universe. 
D) The term is intended to emphasize the fact that an object can become a black hole only once,and a black hole cannot evolve into anything else. 
A) It is the center of the black hole,a place of infinite density where the known laws of physics cannot describe the conditions. 
B) It is the "point of no return" of the black hole;anything closer than this point will not be able to escape the gravitational force of the black hole. 
C) It is the edge of the black hole,where one could leave the observable universe. 
D) The term is intended to emphasize the fact that an object can become a black hole only once,and a black hole cannot evolve into anything else.

Question 18

What is the basic definition of a black hole?

Accepted Answer

A) any compact mass that emits no light 
B) a dead star that has faded from view 
C) any object from which the escape velocity exceeds the speed of light 
D) any object made from dark matter 
E) a dead galactic nucleus that can only be viewed in infrared 
A) any compact mass that emits no light 
B) a dead star that has faded from view 
C) any object from which the escape velocity exceeds the speed of light 
D) any object made from dark matter 
E) a dead galactic nucleus that can only be viewed in infrared

Question 19

There is no upper limit to the mass of a neutron star.

Accepted Answer

A) True 
 B)False

Question 20

The remnant left behind from a white-dwarf supernova is a neutron star.

Accepted Answer

A) True 
 B)False

Exam 18: The Bizarre Stellar Graveyard

Black holes,by definition,cannot be observed directly.What observational evidence do scientists have of their existence?

What do we mean by the event horizon of a black hole?

Neutron stars are the densest objects that we can observe in the universe.

The total energy released during a neutron star merger can be even greater than that of a massive star supernova.

What do we mean by the singularity of a black hole?

From a theoretical standpoint,what is a pulsar?

Scientists have detected thousands of gamma ray bursts.The evidence suggests that most or all of these bursts

Why is there an upper limit to the mass of a white dwarf?

If you were to come back to our Solar System in 6 billion years,what might you expect to find?

What is an X-ray burster? What causes the X-ray bursts?

Each Voyager spacecraft carries a "postcard" designed to be understandable to any aliens that might someday encounter it.On the "postcard," scientists pinpointed the location of Earth by triangulating it between pulsars.Why did the scientists choose pulsars rather than some other type of star?

Which of the following best describes why a white dwarf cannot have a mass greater than the 1.4-solar-mass limit?

How do we know that pulsars are neutron stars?

Which of the following is not true about differences between novae and supernovae?

What do we mean by the singularity of a black hole?

What is the basic definition of a black hole?

There is no upper limit to the mass of a neutron star.

The remnant left behind from a white-dwarf supernova is a neutron star.

A Modern View of the Universe

Discovering the Universe for Yourself

The Science of Astronomy

Making Sense of the Universe: Understanding Motion, Energy, and Gravity

Light and Matter: Reading Messages from the Cosmos

Telescopes: Portals of Discovery

Our Planetary System

Formation of the Solar System

Planetary Geology: Earth and the Other Terrestrial Worlds

Planetary Atmospheres: Earth and the Other Terrestrial Worlds

Jovian Planet Systems

Asteroids, Comets, and Dwarf Planets: Their Nature, Orbits, and Impacts

Other Planetary Systems: The New Science of Distant Worlds

Our Star

Surveying the Stars

Star Birth

Star Stuff

Our Galaxy

Galaxies and the Foundations of Modern Cosmology

Galaxy Evolution

The Birth of the Universe

Dark Matter, Dark Energy, and the Fate of the Universe

Life in the Universe

Celestial Timekeeping and Navigation

Space and Time

Spacetime and Gravity

Building Blocks of the Universe

Filters