Chapter 18 Homework 15 The Bizzare Stellar Graveyard

Question 1

A white dwarf is _________.

what most stars become when they die
an early stage of a neutron star
a precursor to a black hole
a brown dwarf that has exhausted its fuel for nuclear fusion

Answer 1

what most stars become when they die

Question 2

A typical white dwarf is _________.

as massive as the Sun but only about as large in size as Jupiter
about the same size and mass as the Sun but much hotter
as massive as the Sun but only about as large in size as Earth
as large in diameter as the Sun but only about as massive as Earth

Answer 2

as massive as the Sun but only about as large in size as Earth

Question 3

The maximum mass of a white dwarf is _________.

about 1.4 times the mass of our Sun
limitless; there is no theoretical limit to the maximum mass of a white dwarf
about 3 times the mass of our Sun
about the mass of our Sun

Answer 3

about 1.4 times the mass of our Sun

Question 4

A neutron star is _________.

an object that will ultimately become a black hole
the remains of a star that died by expelling its outer layers in a planetary nebula
a star made mostly of elements with high atomic mass numbers, so that they have lots of neutrons
the remains of a star that died in a massive star supernova (if no black hole was created)

Answer 4

the remains of a star that died in a massive star supernova (if no black hole was created)

Question 5

A typical neutron star is more massive than our Sun and about the size (radius) of _________.

a small asteroid (10 km in diameter)
Jupiter
Earth
the Moon

Answer 5

a small asteroid (10 km in diameter)

Question 6

If you had something the size of a sugar cube that was made of neutron star matter, it would weigh _________.

as much as the entire Earth
about as much as a large mountain
about 50 pounds
about as much as a truck

Answer 6

about as much as a large mountain

Question 7

Pulsars are thought to be _________.

unstable high-mass stars
accreting white dwarfs
accreting black holes
rapidly rotating neutron stars

Answer 7

rapidly rotating neutron stars

Question 8

What is the basic definition of a black hole?

a dead star that has faded from view
any object made from dark matter
a compact mass that emits no visible light
an object with gravity so strong that not even light can escape

Answer 8

an object with gravity so strong that not even light can escape

Question 9

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

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

Answer 9

It is the point beyond which neither light nor anything else can escape.

Question 10

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

It is the center of the black hole, a place of infinite density where the known laws of physics cannot describe the conditions.
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.
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.
It is the edge of the black hole, where one could leave the observable universe.

Answer 10

It is the center of the black hole, a place of infinite density where the known laws of physics cannot describe the conditions.

Question 11

The radius of a white dwarf is determined by a balance between the inward force of gravity and the outward push of _________.

Answer 11

electron degeneracy pressure

Question 12

A(n) _______ occurs when hydrogen fusion ignites on the surface of a white dwarf in a binary system.

Answer 12

nova

Question 13

A(n) ________ occurs when fusion creates iron in the core of a star.

Answer 13

massive star supernova

Question 14

A white dwarf in a close binary system will explode as a supernova if it gains enough mass to exceed the _____________

Answer 14

white dwarf limit (1.4 solar masses).

Question 15

A(n) __________ consists of hot, swirling gas captured by a white dwarf ( or neutron star or black hole ) from a binary companion star.

Answer 15

accretion disk

Question 16

A(n) ________ can occur only in a binary system, and all such events are thought to have the same luminosity.

Answer 16

white dwarf supernova

Question 17

Listed following are several astronomical objects. Rank these objects based on their diameter, from largest to smallest. (Note that the neutron star and black hole in this example have the same mass to make your comparison easier, but we generally expect black holes to have greater masses than neutron stars.)

main-sequence star of spectral type a
jupiter
a one solar mass white dwarf
the moon
a two solar mass neutron star
event horizon of a two solar mass black hole

Answer 17

main-sequence star of spectral type a
jupiter
a one solar mass white dwarf
the moon
a two solar mass neutron star
event horizon of a two solar mass black hole

Question 18

Listed following are several astronomical objects. Rank these objects based on their mass, from largest to smallest. (Be sure to notice that the main-sequence star here has a different spectral type from the one in Part A.)

a typical black hole (formed in supernova)
a typical neutron star
a one solar mass white dwarf
main-sequence star of spectral type m
jupiter
the moon

Answer 18

a typical black hole (formed in supernova)
a typical neutron star
a one solar mass white dwarf
main-sequence star of spectral type m
jupiter
the moon

Question 19

Listed following are several astronomical objects. Rank these objects based on their density, from highest to lowest.

singularity of a black hole
a typical neutron star
a one solar mass white dwarf
a main-sequence star

Answer 19

singularity of a black hole
a typical neutron star
a one solar mass white dwarf
a main-sequence star

Question 20

Listed following are distinguishing characteristics of different end states of stars. Match these to the appropriate consequence of stellar death. White Dwarf

has a mass no greater than 1.4 Msun
supported by electron degeneracy pressure
in a binary system, it can explode as a supernova,
typically about the size (diameter) of Earth
sometimes appears as a pulsar
usually has a very strong magnetic field
view from afar, time stops at its event horizon
size defined by its schwarzschild radius

Answer 20

has a mass no greater than 1.4 Msun
supported by electron degeneracy pressure
in a binary system, it can explode as a supernova,
typically about the size (diameter) of Earth

Question 21

Listed following are distinguishing characteristics of different end states of stars. Match these to the appropriate consequence of stellar death. Neutron Star

has a mass no greater than 1.4 Msun
supported by electron degeneracy pressure
in a binary system, it can explode as a supernova,
typically about the size (diameter) of Earth
sometimes appears as a pulsar
usually has a very strong magnetic field
view from afar, time stops at its event horizon
size defined by its schwarzschild radius

Answer 21

sometimes appears as a pulsar

usually has a very strong magnetic field

Question 22

Listed following are distinguishing characteristics of different end states of stars. Match these to the appropriate consequence of stellar death. Black hole

has a mass no greater than 1.4 Msun
supported by electron degeneracy pressure
in a binary system, it can explode as a supernova,
typically about the size (diameter) of Earth
sometimes appears as a pulsar
usually has a very strong magnetic field
view from afar, time stops at its event horizon
size defined by its schwarzschild radius

Answer 22

view from afar, time stops at its event horizon

size defined by its schwarzschild radius

Question 23

The following items describe observational characteristics that could indicate that an object is either a white dwarf or a neutron star. Match each characteristic to the correct object.
White dwarf:

may be in a binary system that undergoes nova explosions.
may be surrounded by a planetary nebula.
emits most strongly in visible and ultraviolet.
may be surrounded by a supernova remnant.
may repeatedly dim and brighten more than once per second.
can have a mass of 1.5 solar masses.
may be in a binary system that undergoes x-ray bursts.

Answer 23

may be in a binary system that undergoes nova explosions.
may be surrounded by a planetary nebula.
emits most strongly in visible and ultraviolet.

Question 24

The following items describe observational characteristics that could indicate that an object is either a white dwarf or a neutron star. Match each characteristic to the correct object.
Neutron star:

may be in a binary system that undergoes nova explosions.
may be surrounded by a planetary nebula.
emits most strongly in visible and ultraviolet.
may be surrounded by a supernova remnant.
may repeatedly dim and brighten more than once per second.
can have a mass of 1.5 solar masses.
may be in a binary system that undergoes x-ray bursts.

Answer 24

may be surrounded by a supernova remnant.
may repeatedly dim and brighten more than once per second.
can have a mass of 1.5 solar masses.
may be in a binary system that undergoes x-ray bursts.

Question 25

The following items describe observational characteristics that may indicate that an object is either a neutron star or a black hole. Match each characteristic to the correct object; if the characteristic could apply to both types of object, choose the bin labeled “Both neutron stars and black holes.”
Neutron star only:

may emit rapid pulses of radio waves.
may be in binary system that undergoes x-ray bursts.
is detectable only if it is accreting gas from other objects.
can have a mass of 10 solar masses
may be located in a x-ray binary.
may be surrounded by a supernova remnant.

Answer 25

may emit rapid pulses of radio waves.

may be in binary system that undergoes x-ray bursts.

Question 26

The following items describe observational characteristics that may indicate that an object is either a neutron star or a black hole. Match each characteristic to the correct object; if the characteristic could apply to both types of object, choose the bin labeled “Both neutron stars and black holes.”
Black hole only:

may emit rapid pulses of radio waves.
may be in binary system that undergoes x-ray bursts.
is detectable only if it is accreting gas from other objects.
can have a mass of 10 solar masses
may be located in a x-ray binary.
may be surrounded by a supernova remnant.

Answer 26

is detectable only if it is accreting gas from other objects.
can have a mass of 10 solar masses

Question 27

The following items describe observational characteristics that may indicate that an object is either a neutron star or a black hole. Match each characteristic to the correct object; if the characteristic could apply to both types of object, choose the bin labeled “Both neutron stars and black holes.”
Both Neutron star and black holes:

may emit rapid pulses of radio waves.
may be in binary system that undergoes x-ray bursts.
is detectable only if it is accreting gas from other objects.
can have a mass of 10 solar masses
may be located in a x-ray binary.
may be surrounded by a supernova remnant.

Answer 27

may be located in a x-ray binary.

may be surrounded by a supernova remnant

Question 28

The Chandra X-Ray Observatory has detected X rays from a star system that contains a main-sequence star of spectral type B6. The X-ray emission is strong and fairly steady, and no sudden bursts have been observed. Which of the following statements are reasonable conclusions about this system?
Check all that apply.

Some time in the next few decades, this system will undergo a nova explosion.
The main-sequence star orbits either a white dwarf or a neutron star.
Gas from the main-sequence star makes an accretion disk around another object.
The main-sequence star orbits either a neutron star or a black hole.
The main-sequence star must orbit a neutron star.
The main-sequence star must orbit a white dwarf.
The main-sequence star must orbit a black hole.
The main-sequence star is emitting X rays.

Answer 28

Gas from the main-sequence star makes an accretion disk around another object.
The main-sequence star orbits either a neutron star or a black hole.

Question 29

What is the key observation needed to determine whether the compact object in Part C is a neutron star or a black hole?

Study the X-ray emission to determine the temperature of the gas in the accretion disk.
Measure Doppler shifts in the spectrum of the main-sequence star so that you can determine the mass of the compact object.
Obtain high-resolution images of the compact object, so that you can determine whether it emits any light.

Answer 29

Measure Doppler shifts in the spectrum of the main-sequence star so that you can determine the mass of the compact object.

Question 30

What do we mean by dimension in the context of relativity?

the letter used to represent length mathematically
the number of sides that we can see when we look at an object
the number of independent directions in which movement is possible
the size of an object

Answer 30

the number of independent directions in which movement is possible

Question 31

What is spacetime?

It's a graph with four axes.
It is a way of viewing objects from different angles.
Time that we measure when traveling in space.
The combination of 3-dimensional space and 1-dimensional time into a combined 4-dimensional space.

Answer 31

The combination of 3-dimensional space and 1-dimensional time into a combined 4-dimensional space.

Question 32

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

It is the "bottomless pit" of the black hole.
It is the center of the black hole.
It is the place where time begins to slow down as you approach a black hole.
It is the boundary within which events in the black hole cannot influence events in the outside universe.

Answer 32

It is the boundary within which events in the black hole cannot influence events in the outside universe.

Question 33

What do we mean by gravitational time dilation?

It is the idea that clocks run slow for people moving at high speed past you.
It is the idea that time runs slower in places where gravity is stronger.
It is the idea that everyone measures time differently, depending on his/her reference frame.
It is the idea that clocks run faster in stronger gravitational fields.

Answer 33

It is the idea that time runs slower in places where gravity is stronger.

Question 34

The figures below show several different astronomical objects. Rank the objects based on the amount that spacetime is curved (relative to flat spacetime) at a distance of 10 AU from the center of each of the objects, from least to greatest. If two (or more) cases are equal, show this equality by dragging one figure on top of the other(s).

Answer 34

all the same

Question 35

The figures below show several different astronomical objects. Rank the objects based on the strength of the gravitational force that would be felt by a spacecraft traveling at a distance of 10 AU from the center of each of the objects, from weakest to strongest. If the gravitational force is equal for two (or more) cases, show this equality by dragging one figure on top of the other(s).

Answer 35

all the same

Question 36

The figures below show several different astronomical objects. Rank the objects based on the amount that spacetime is curved (relative to flat spacetime) very near the surface (or event horizon) of the objects, from least to greatest.

red giant 1msun 100rsun
the sun
white dwarf 1 msun .01r sun
black hole 1msun 3km

Answer 36

red giant
the sun
white dwarf
black hole

Question 37

The figures below show several different astronomical objects. Rank the objects based on the acceleration a spaceship would have as it passed very near the surface (or event horizon) of each object, from smallest to largest.

red giant 1msun 100rsun
the sun
white dwarf 1 msun .01r sun
black hole 1msun 3km

Answer 37

red giant 1msun 100rsun
the sun
white dwarf 1 msun .01r sun
black hole 1msun 3km

Question 38

From the viewpoint of an observer in the orbiting rocket, what happens to time on the other rocket as it falls toward the event horizon of the black hole?

Time runs increasingly faster as the rocket approaches the black hole.
Time runs increasingly slower as the rocket approaches the black hole.
Time is always the same on both rockets.

Answer 38

Time runs increasingly slower as the rocket approaches the black hole.

Question 39

As the falling rocket plunges toward the event horizon, an observer in the orbiting rocket would see that the falling rocket __________.

slows down as it approaches the event horizon, and never actually crosses the event horizon
slows down near the event horizon so that it crosses the event horizon at a low speed
moves at constant speed as it approaches and crosses the event horizon
accelerates as it falls, and crosses the event horizon at high speed

Answer 39

slows down as it approaches the event horizon, and never actually crosses the event horizon

Question 40

From Part B, you know that from afar we’ll never see the in-falling rocket cross the event horizon, yet it will still eventually disappear from view. Why?

Even though you won’t see it cross the event horizon, it does cross it and that means you can no longer see it.
Its light will become so redshifted that it will be undetectable.
The black hole’s blackness will drown out the light of the rocket.
Tidal forces will squeeze the in-falling rocket to an undetectably thin line.

Answer 40

Its light will become so redshifted that it will be undetectable.

Question 41

If you were inside the rocket that falls toward the event horizon, you would notice your own clock to be running __________.

increasingly faster as you approach the event horizon
at a constant, normal rate as you approach the event horizon
increasingly slower as you approach the event horizon

Answer 41

at a constant, normal rate as you approach the event horizon

Question 42

If you were inside the rocket that falls toward the event horizon, from your own viewpoint you would __________.

slow down and come to a stop at the event horizon
slow down and cross the event horizon at low speed
accelerate as you fall and cross the event horizon completely unhindered

Answer 42

accelerate as you fall and cross the event horizon completely unhindered

Question 43

Sirius, the brightest star in the night sky, is actually a binary star system: Sirius A is main-sequence star and Sirius B is a white dwarf. Nearly all the visible light we see from Sirius comes from Sirius A. But when we photograph the system with X-ray light, as shown here, Sirius B is the brighter of the two stars. Why?

Sirius B is brighter in X rays because it is a nova.
As a white dwarf, Sirius B is much hotter than Sirius A and thus emits more X rays.
Sirius B is brighter in X rays because it is a white dwarf supernova.
As a white dwarf, Sirius B is too small to emit visible light but not too small to emit X rays.

Answer 43

As a white dwarf, Sirius B is much hotter than Sirius A and thus emits more X rays.

Question 44

Which of the following diagrams shows Earth and a neutron star correctly scaled?

Answer 44

A neutron star is typically about 10 km in radius, compared to Earth’s more than 6,000 km radius

Question 45

Imagine that you were driving a spaceship close to a black hole, without falling in. If you were able to observe and map out the black hole’s event horizon, what would be the true shape of it?

Answer 45

Black holes are in fact spherical objects, just like neutron stars, white dwarfs, and any other stars in the universe. The 2-dimensional grid used to represent how spacetime curves around a black holes is simply a way to visualize the space around a black hole– it is not a literal picture of what a black hole looks like.

Question 46

A spacecraft is on a trajectory that happens to be taking it near a black hole. Which diagram shows how the spacecraft’s orbit will be affected?

Answer 46

Except very close to its event horizon, the black hole’s gravity is no different than the gravity of any other object of the same mass. Therefore all orbits must be either bound ellipses or unbound paths (parabola or a hyperbola); the spacecraft coming from afar is on an unbound trajectory.

Question 47

This series of images shows the pulsar at the center of the Crab Nebula looking bright every 0.033 second. Based on these data and current theory of pulsars, what can we conclude?

The pulsar is a neutron star that makes one full rotation every 0.033 second.
The pulsar is a neutron star whose magnetic field switches on and off every 0.033 second.
The pulsar has an accretion disk that undergoes an X-ray burst every 0.033 second.
The pulsar is part of a close binary star system in which the two stars complete an orbit every 0.033 second.

Answer 47

The pulsar is a neutron star that makes one full rotation every 0.033 second.

Question 48

This painting shows an accretion disk around a black hole in a close binary star system. What physical law explains why matter flowing from the companion star orbits rapidly as it nears the black hole?

Newton's third law of motion.
Einstein's general theory of relativity.
The law of conservation of angular momentum.
Kepler's second law of planetary motion.

Answer 48

The law of conservation of angular momentum.

Question 49

The white dwarf that remains when our Sun dies will be mostly made of ______.

carbon
neutrons
helium
hydrogen

Answer 49

carbon

Question 50

According to present understanding, a nova is caused by _________.

a white dwarf that gains enough mass to exceed the 1.4-solar-mass limit
carbon fusion in the core of a white dwarf
hydrogen fusion on the surface of a neutron star
hydrogen fusion on the surface of a white dwarf

Answer 50

hydrogen fusion on the surface of a white dwarf

Question 51

Will our Sun ever undergo a white dwarf supernova explosion? Why or why not?

Yes, right at the end of its double-shell burning stage of life.
Yes, about a million years after it becomes a white dwarf.
No, because it is not orbited by another star.
No, because the Sun's core will never be hot enough to fuse carbon and other heavier elements into iron.

Answer 51

No, because it is not orbited by another star.

Question 52

Which of statement below about black holes is not true?

Although we are not 100% certain that black holes exist, we have strong observational evidence in favor of their existence.
A spaceship passing near a 10 solar mass black hole is much more likely to be destroyed than a spaceship passing at the same distance from the center of a 10 solar mass main-sequence star.
If you fell into a black hole, you would experience time to be running normally as you plunged rapidly across the event horizon.
If you watch someone else fall into a black hole, you will never see him (or her) cross the event horizon; you'll only see him fade from view as the light he emits or reflects becomes more and more redshifted.

Answer 52

A spaceship passing near a 10 solar mass black hole is much more likely to be destroyed than a spaceship passing at the same distance from the center of a 10 solar mass main-sequence star.

Question 53

Suppose you drop a clock toward a black hole. As you look at the clock from a high orbit, what will you notice?

The clock will fall faster and faster, reaching the speed of light as it crosses the event horizon.
The clock will fall toward the black hole at a steady rate, so that you'll see it plunge through the event horizon within just a few minutes.
Time on the clock will run slower as it approaches the black hole, and light from the clock will be increasingly redshifted.
Time on the clock will run faster as it approaches the black hole, and light from the clock will be increasingly blueshifted.

Answer 53

Time on the clock will run slower as it approaches the black hole, and light from the clock will be increasingly redshifted.

Question 54

Which of the following observatories is most likely to discover a black hole in a binary system?

the Chandra X-Ray Observatory
the Arecibo Radio Observatory
the SOFIA airborne infrared observatory
the Hubble Space Telescope

Answer 54

the Chandra X-Ray Observatory