Chapter 16, 17, and 18 Astronomy Exam

The interstellar clouds called molecular clouds are _______.

a)the clouds in which elements such as carbon, nitrogen, and oxygen are made
b) the hot clouds of gas expelled by dying stars
c)the cool clouds in which stars form
d)clouds that are made mostly of complex molecules such as carbon dioxide and sulfur dioxide

c) the cool clouds in which stars form

Why are the very first stars thought to have been much more massive than the Sun?

a) The clouds that made them were much more massive than today’s star-forming clouds.
b) The temperatures of the clouds that made them were higher because they consisted entirely of hydrogen and helium.
c)Star-forming clouds were much denser early in time.

b) The temperatures of the clouds that made them were higher because they consisted entirely of hydrogen and helium.

Which part of the electromagnetic spectrum generally gives us our best views of stars forming in dusty clouds?
Which part of the electromagnetic spectrum generally gives us our best views of stars forming in dusty clouds?
a) blue light
b) visible light
c) ultraviolet
d) infrared

d) d) infrared

Most interstellar clouds remain stable in size because the force of gravity is opposed by _______ within the cloud.
a) degeneracy pressure
b) stellar winds
c) radiation pressure
d) thermal pressure

d) thermal pressure

Which of the following statements is probably true about the very first stars in the universe?

a) They were made from pure energy.
b) They were made only from hydrogen and helium.
c) They were probably orbited only by terrestrial planets, but no jovian planets.
d) They were made approximately of 98 percent hydrogen and helium, and 2 percent of heavier elements.

b) They were made only from hydrogen and helium

The water molecules now in your body were once part of a molecular cloud. Only about onemillionth of the mass of a molecular cloud is in the form of water molecules, and the mass density of such a cloud is roughly 4.0×10−21 g/cm^3

Part A

Estimate the volume of a piece of molecular cloud that has the same amount of water as your body.

Part B

How does this volume compare with the volume of the entire Earth?

Part A: Vcloud= 1.0×1031 cm^3 Part B: Vcloud=9200 VEarth

What law explains why a collapsing cloud usually forms a protostellar disk around a protostar?

a) Kepler’s third law
b) conservation of angular momentum
c) Wien’s law
d) the universal law of gravitation

b) conservation of angular momentum

Which of the following statements about brown dwarfs is NOT true?

a) Brown dwarfs eventually collapse to become white dwarfs.
b) All brown dwarfs have masses less than about 8 percent that of our Sun.
c)Brown dwarfs form like ordinary stars but are too small to sustain nuclear fusion in their cores.
d)Brown dwarfs are supported against gravity by degeneracy pressure, which does not depend on the object’s temperature.

a) Brown dwarfs eventually collapse to become white dwarfs.

What can we learn about a star from a life track on an H-R diagram?

a) the star’s age
b) the star’s current stage of life
c) The surface temperature and luminosity the star will have at each stage of its life.
d) how the star’s distance from Earth varies at different times in its life

c) The surface temperature and luminosity the star will have at each stage of its life.

Which star spends the longest time in the protostellar phase of life?

a) a 4 solar mass star
b) a 3 solar mass star
c) a 1 solar mass star
d) a 5 solar mass star
e) a 2 solar mass star

c) a 1 solar mass star

What happens within a contracting cloud in which gravity is stronger than pressure and temperature remains constant?

a) It breaks into smaller fragments.
b) Thermal pressure starts to push back more effectively against gravity.
c) It traps all the energy released by gravitational contraction.

a) It breaks into smaller fragments

Which kind of pressure prevents stars of extremely large mass from forming?

a) thermal pressure
b) radiation pressure
c) degeneracy pressure

b) radiation pressure

By mass, the interstellar medium in our region of the Milky Way consists of

a) 70% Hydrogen, 30% Helium.
b) 70% Hydrogen, 28% Helium, 2% heavier elements.
c) 50% Hydrogen, 50% Helium.
d) 70% Hydrogen, 20% Helium, 10% heavier elements.
e) 50% Hydrogen, 30% Helium, 20% heavier elements.

b) 70% Hydrogen, 28% Helium, 2% heavier elements.

The most abundant molecule in molecular clouds is

a) HHe.
b) CO.
c) H2O.
d) He2.
e) H2

e) H2

If you wanted to observe stars behind a molecular cloud, in what wavelength of light would you most likely observe?

a) ultraviolet
b) gamma-ray
c) visible
d) infrared
e) X-ray

d) infrared

How do astronomers infer the presence of magnetic fields in molecular clouds?

a) by measuring the polarization of starlight passing through the cloud
b) by measuring the Doppler shifts of emission lines from gas clumps in the cloud
c) by measuring the amount by which gravity is reduced
d) by measuring the amount of interstellar reddening
e) by measuring the infrared light emitted by the cloud

a) by measuring the polarization of starlight passing through the cloud

When is thermal energy trapped in the dense center of a cloud?

a) when magnetic fields trap the radiation
b) when the cloud cools down so much that less light escapes than is produced by contraction
c) when the cloud becomes so hot and dense that nuclear fusion begins
d) when excited molecules collide with other molecules before they can release a photon
e) when the gravity becomes so strong that photons cannot escape

d) when excited molecules collide with other molecules before they can release a photon

Which of these colors of light passes most easily through interstellar clouds?

a)blue light
b) red light
c) green light

b) red light

How long does the protostellar stage last for a star like our Sun?

a) 3 million years
b) 10 million years
c) 30 million years
d) 1 million years
e) 100 million years

c) 30 million years

What happens to the surface temperature and luminosity when gravity first assembles a protostar from a collapsing cloud?

a) Its surface temperature and luminosity increase.
b) Its surface temperature remains the same and its luminosity decreases.
c) Its surface temperature decreases and its luminosity increases.
d) Its surface temperature and luminosity decrease.
e) Its surface temperature and luminosity remain the same.

a) Its surface temperature and luminosity increase.

When does hydrogen first begin to fuse into helium in the star formation process?

a) when the protostar undergoes radiative contraction
b) when the protostars undergoes convective contraction
c) when the cloud first begins to contract
d) when the thermal pressure is trapped at the center of the cloud
e) only when the star reaches the main-sequence

a) when the protostar undergoes radiative contraction

What prevents a brown dwarf from undergoing nuclear fusion?

a) There are too many heavy elements and not enough hydrogen for fusion to occur in a self-sustaining way.
b) Radiation pressure halts the contraction of a protostar so the core never becomes hot or dense enough for nuclear fusion.
c) Degeneracy pressure halts the contraction of a protostar so the core never becomes hot or dense enough for nuclear fusion.
d) The surface temperature never rises high enough for the radiation to be trapped and heat their interior to the temperatures required for nuclear fusion.
e) There is not enough mass to maintain nuclear reactions in a self-sustaining way.

c) Degeneracy pressure halts the contraction of a protostar so the core never becomes hot or dense enough for nuclear fusion.

What is the eventual fate of a brown dwarf?

a) Gravity ultimately "wins" and it becomes a small black hole.
b) It gradually contracts and heats up until nuclear fusion ignites in its interior and it becomes a faint star.
c) It remains the same forever.
d) It becomes ever denser and hotter until it becomes a white dwarf.
e) It gradually cools down and becomes ever dimmer.

e) It gradually cools down and becomes ever dimmer.

Which of the following stars will live longest?

a) 1 solar mass star
b) 4 solar mass star
c) 3 solar mass star
d) 2 solar mass star

a) 1 solar mass star

The following figures show various stages during the life of a star with the same mass as the Sun. Rank the stages based on when they occur, from first to last.

contracting cloud of gas and dust prostar main-sequence G-Star Red Giant Planetary nebula White Dwarf

During its final days as a red giant, the Sun will reach a peak luminosity of about 3000LSun. Earth will therefore absorb about 3,000 times as much solar energy as it does now, and it will need to radiate 3,000 times as much thermal energy to keep its surface temperature in balance.

Estimate the temperature Earth’s surface will need to attain in order to radiate that much thermal energy. You will need to use the formula for emitted power per unit area. (Assume that Earth’s temperature today is around 300 K.)

ANSWER: TEarth= 2220K WORK: E(now)=s (300)^4 3000E(now)=sT^4 where T is the temp needed in the future to maintain balance take the ratio of these equations: 3000E(now)/E(now) = s T^4/(300)^4 3000×300^4=T^4 T=(3000)^(1/4) * 300 T=7.4*300=2220K; the earth will glow like a dull, red object

Choose the correct explanation of how do red giants manufacture carbon-rich dust grains, and why are these important to life.

a) The radiation in a low-mass star in its final stages of life dredges up carbon from the core and brings it to the surface. Because the carbon can then be lost via the stellar winds, these stars seed the interstellar medium with carbon, including the carbon that is used for life on Earth.
b) The convection in a low-mass star in its final stages of life dredges up carbon from the core and brings it to the surface. Because the carbon can then be lost via the stellar winds, these stars seed the interstellar medium with carbon, including the carbon that is used for life on Earth.
c) The convection in a low-mass star in its final stages of life dredges up carbon from the surface and brings it to the core. Because the carbon can then be lost via the stellar winds, these stars seed the interstellar medium with carbon, including the carbon that is used for life on Earth.
d) The radiation in a low-mass star in its final stages of life dredges up carbon from the surface and brings it to the core. Because the carbon can then be lost via the stellar winds, these stars seed the interstellar medium with carbon, including the carbon that is used for life on Earth.

b) The convection in a low-mass star in its final stages of life dredges up carbon from the core and brings it to the surface. Because the carbon can then be lost via the stellar winds, these stars seed the interstellar medium with carbon, including the carbon that is used for life on Earth.

The ultimate fate of our Sun is to _____.

a) become a black hole
b) become a rapidly spinning neutron star
c) explode in a supernova
d) become a white dwarf that will slowly cool with time

d) become a white dwarf that will slowly cool with time

Which of these elements had to be made in a supernova explosion?

a) calcium
b) uranium
c) oxygen

b) uranium

What would stars be like if carbon had the smallest mass per nuclear particle?

a) Supernovae would be more common.
b) Supernovae would never occur.
c) High-mass stars would be hotter.

a) Supernovae would be more common.

3 red/gray balls -> 1 big ball + energy

In this diagram, red balls represent protons and gray balls represent neutrons. What reaction is being shown?

a) fusion of carbon into oxygen
b) fusion of hydrogen into helium
c) the "iron catastrophe" that initiates a supernova
d) fusion of helium into carbon

d) fusion of helium into carbon

Our Sun is considered to be a ______.

a) low-mass star
b) brown dwarf
c) intermediate-mass star
d) high-mass star

a) low-mass star

Which of the following types of data provide evidence that helps us understand the life tracks of low-mass stars?

a) spacecraft observations of the Sun
b) H-R diagrams of globular clusters
c) observing a low-mass star over many years
d) H-R diagrams of open clusters

b) H-R diagrams of globular cluste

Why is a 1 solar-mass red giant more luminous than a 1 solar-mass main-sequence star?

a) The red giant’s surface is hotter.
b) Fusion reactions are producing energy at a greater rate in the red giant.
c) The red giant is more massive.
d) The red giant has a hotter core.

b) Fusion reactions are producing energy at a greater rate in the red giant.

Which of the following describes a star with a hydrogen-burning shell and an inert helium core?

a) It is a subgiant that grows in luminosity until helium fusion begins in the central core.
b) It is a subgiant that gradually grows dimmer as its hydrogen-burning shell expands and cools.
c) It is what is known as a helium-burning star, which has both helium fusion in its core and hydrogen fusion in a shell.
d) It is a red giant that grows in luminosity until it dies in a planetary nebula.

a) It is a subgiant that grows in luminosity until helium fusion begins in the central core.

Which of the following observations would not be likely to provide information about the final, explosive stages of a star’s life?

a) studying the light rings around Supernova 1987A in the Large Magellanic Cloud
b) neutrino detections from nearby supernovae
c) decades of continuous monitoring of red giants in a globular cluster
d) observing the structures of planetary nebulae

c) decades of continuous monitoring of red giants in a globular cluster

Which is more common: a star blows up as a supernova, or a star forms a planetary nebula/white dwarf system?

a) They both occur in about equal numbers.
b) Supernovae are more common.
c) Planetary nebula formation is more common.
d) It is impossible to say.

c) Planetary nebula formation is more common.

Carbon fusion occurs in high-mass stars but not in low-mass stars because _________.

a) only high-mass stars do fusion by the CNO cycle
b) the cores of low-mass stars never get hot enough for carbon fusion
c) the cores of low-mass stars never contain significant amounts of carbon
d) carbon fusion can occur only in the stars known as carbon stars

b) the cores of low-mass stars never get hot enough for carbon fusion

Which of the following statements about various stages of core nuclear burning (hydrogen, helium, carbon, etc.) in a high-mass star is not true?

a) Each successive stage creates an element with a higher atomic number and atomic mass number.
b) As each stage ends, the core shrinks and heats further.
c) As each stage ends, the reactions that occurred in previous stages continue in shells around the core.
d) Each successive stage lasts for approximately the same amount of time

d) Each successive stage lasts for approximately the same amount of time

Which event marks the beginning of a supernova?

a) The beginning of neon burning in an extremely massive star.
b) The sudden initiation of the CNO cycle.
c) The sudden collapse of an iron core into a compact ball of neutrons.
d) The onset of helium burning after a helium flash.

c) The sudden collapse of an iron core into a compact ball of neutrons.

Suppose that the star Betelgeuse (the upper left shoulder of Orion) were to supernova tomorrow (as seen here on Earth). What would it look like to the naked eye?

a) Because the supernova destroys the star, Betelgeuse would suddenly disappear from view.
We’d see a cloud of gas expanding away from the position where
b) Betelgeuse used to be. Over a period of a few weeks, this cloud would fill our entire sky.
c) Betelgeuse would remain a dot of light but would suddenly become so bright that for a few weeks we’d be able to see this dot in the daytime.
d) Betelgeuse would suddenly appear to grow larger in size, soon reaching the size of the full Moon. It would also be about as bright as the full Moon

c) Betelgeuse would remain a dot of light but would suddenly become so bright that for a few weeks we’d be able to see this dot in the daytime.

Suppose that hydrogen, rather than iron, had the lowest mass per nuclear particle. Which of the following would be true?

a) Stars would be brighter.
b) All stars would be red giants.
c) Nuclear fusion could not power stars.
d) Stars would be less massive.

c) Nuclear fusion could not power stars

Observations show that elements with atomic mass numbers divisible by 4 (such as oxygen-16, neon-20, and magnesium-24) tend to be more abundant in the universe than elements with atomic mass numbers in between. Why do we think this is the case?

a) At the end of a high-mass star’s life, it produces new elements through a series of helium capture reactions.
b) This pattern in elemental abundances was apparently determined during the first few minutes after the Big Bang.
c) The apparent pattern is thought to be a random coincidence.
d) Elements with atomic mass numbers divisible by 4 tend to be more stable than elements in between.

a) At the end of a high-mass star’s life, it produces new elements through a series of helium capture reactions.

A spinning neutron star has been observed at the center of a ______.

a) protostar
b) planetary nebula
c) supernova remnant
d) red supergiant

c) supernova remnant

You discover a binary star system in which one star is a 15 M Sun main-sequence star and the other is a 10 M Sun giant. How do we think that a star system such as this might have come to exist?

a) The two stars probably were once separate, but became a binary when a close encounter allowed their mutual gravity to pull them together.
b) The giant must once have been the more massive star, but it is now less massive because it transferred some of its mass to its companion.
c) Although both stars probably formed from the same clump of gas, the more massive one must have had its birth slowed so that it became a main-sequence stars millions of years later than its less massive companion.
d) The two stars are simply evolving normally and independently, and one has become a giant before the other.

b) The giant must once have been the more massive star, but it is now less massive because it transferred some of its mass to its companion.

Tidal forces are important to the Algol system today but were not important when both stars were still on the main sequence. Why not?

a) Main-sequence stars are too massive to be affected by tidal forces.
b) Main-sequence stars are too big to be affected by tidal forces.
c) Main-sequence stars in a system like the Algol system are small compared to their physical separation.
d) Main-sequence stars are unaffected by tidally induced mass transfer.

c) Main-sequence stars in a system like the Algol system are small compared to their physical separation.

Which two energy sources can help a star maintain its internal thermal pressure?

a) nuclear fission and gravitational contraction
b) nuclear fusion and nuclear fission
c) nuclear fusion and gravitational contraction
d) nuclear fusion and chemical reactions
e) chemical reactions and gravitational contraction

c) nuclear fusion and gravitational contraction

Photographs of many young stars show long jets of material apparently being ejected from their poles.

True
False

true

Which of the following properties make flare stars so active?

a) fast rotation rates
b) deep convection zones
c) convecting cores
d) strong stellar winds
e) both A and B

e) both A and B

Compared to the star it evolved from, a red giant is

a) cooler and dimmer.
b) hotter and brighter.
c) the same temperature and brightness.
d) hotter and dimmer.
e) cooler and brighter.

e) cooler and brighter.

Convection never occurs in the core of any type of star.

True
False

false

When a star exhausts its core hydrogen fuel, the core contracts but the star as a whole expands. Why?

The inner portions are more dense and closer to the gravitational center cause it to fall at a faster rate. Before the outer portions fall in too far the core will start fusion, and it will release stellar energy again which will send the outer portions away from the star

What do all low-mass stars share in common? Why do they differ in their levels of surface activity? What are flare stars?

What do all low-mass stars share in common? Why do they differ in their levels of surface activity? What are flare stars?

Choose the correct explanation, why can the lives of close binary stars differ from those of single stars.

a) Mass exchange between two stars in a close binary system causes some stars with companions to change their masses throughout their lives, altering the life tracks in ways that do not affect single stars.
b) Mass exchange between two stars in a close binary system causes some stars with companions to change their speeds throughout their lives, altering the life tracks in ways that do not affect single stars.
c) Mass exchange between two stars in a close binary system causes some stars with companions to change their temperatures throughout their lives, altering the life tracks in ways that do not affect single stars.
d) Mass exchange between two stars in a close binary system causes some stars with companions to change their trajectories throughout their lives, altering the life tracks in ways that do not affect single stars.

a) Mass exchange between two stars in a close binary system causes some stars with companions to change their masses throughout their lives, altering the life tracks in ways that do not affect single stars.

What is the 4th most abundant element?

oxygen
carbon
beryllium
boron

carbon

According to our modern understanding of the origin of elements, why are hydrogen and helium so much more abundant than any other elements?

a) Modern science is unable to account for their high abundances.
b) They were produced in the Big Bang.
c) They are the most common elements produced in the aftermath of supernova explosions.
d) They are the two elements most commonly produced by fusion in stars.

b) They were produced in the Big Bang.

Notice that nitrogen is less abundant than either carbon or oxygen. This is an example of the more general observation that __________.

a) elements produced by fusion in stars are more common than elements produced in the aftermath of supernova explosions
b) elements with higher atomic numbers are more abundant than elements with lower atomic numbers
c) elements with lower atomic numbers are more abundant than elements with higher atomic numbers
d) elements with even atomic numbers are more abundant than the elements with odd atomic numbers that come between them

d) elements with even atomic numbers are more abundant than the elements with odd atomic numbers that come between them

Overall, careful study of the patterns revealed in the graph of measured element abundances has allowed scientists to __________.

a) test and validate models of how elements are produced by stars
b) learn that most elements are produced in stars with masses similar to the Sun
c) test and validate models of the Big Bang
d) learn that only high-mass stars die in supernova explosions

a) test and validate models of how elements are produced by stars

Choose the correct description of what accretion disks are, and why do we find them only in close binary systems.

a) An accretion disk is a disk of orbiting material that is falling toward a central body, like a white dwarf. We see these only in close binary systems because they require material to be transferred from the stars to the outer space.
b) An accretion disk is a disk of orbiting material that is spreading from a central body, like a white dwarf. We see these only in close binary systems because they require material to be transferred from one star to another.
c) An accretion disk is a disk of orbiting material that is falling toward a central body, like a white dwarf. We see these only in close binary systems because they require material to be transferred from one star to another.
d) An accretion disk is a disk of orbiting material that is spreading from a central body, like a white dwarf. We see these only in close binary systems because they require material to be transferred from the stars to the outer space.

c) An accretion disk is a disk of orbiting material that is falling toward a central body, like a white dwarf. We see these only in close binary systems because they require material to be transferred from one star to another.

Choose the correct explanation of how does the accretion disk provide a white dwarf with a new source of energy that we can detect from Earth.

a) As the material falls onto a white dwarf, gravitational energy is turned into heat. The heat provides the white dwarf with a new energy source, allowing it to glow in the infrared.
b) As the material falls onto a white dwarf, radiation energy is turned into heat. The heat provides the white dwarf with a new energy source, allowing it to glow in the infrared.
c) As the material falls onto a white dwarf, gravitational energy is turned into heat. The heat provides the white dwarf with a new energy source, allowing it to glow in the ultraviolet.
d) As the material falls onto a white dwarf, radiation energy is turned into heat. The heat provides the white dwarf with a new energy source, allowing it to glow in the ultraviolet.

c) As the material falls onto a white dwarf, gravitational energy is turned into heat. The heat provides the white dwarf with a new energy source, allowing it to glow in the ultraviolet

Choose the correct description, of what happens to the electron speeds in a more massive white dwarf.

a) As the mass of a white dwarf increases, the pressure must increase to resist gravity. To do this, the electrons must move faster.
b) As the mass of a white dwarf increases, the pressure must decrease to resist gravity. To do this, the electrons must move slower.
c) As the mass of a white dwarf increases, the pressure must decrease to resist gravity. To do this, the electrons must move faster.
d) As the mass of a white dwarf increases, the pressure must increase to resist gravity. To do this, the electrons must move slower.

a) As the mass of a white dwarf increases, the pressure must increase to resist gravity. To do this, the electrons must move faster.

Choose the correct description, how does this behavior lead to the white dwarf limit for mass.

a) If mass of the white dwarf becomes so great that the electrons would have to move faster than light to resist the gravity, the white dwarf must explode as a supernova. This limit is about 1.4 MSun.
b) If mass of the white dwarf becomes so great that the electrons would have to move faster than light to resist the gravity, the white dwarf must collapse into a neutron star. This limit is about 1.4 MSun.
c) If mass of the white dwarf becomes so great that the electrons would have to move faster than light to resist the gravity, the white dwarf must collapse into a neutron star. This limit is about 2.4 MSun.
d) If mass of the white dwarf becomes so great that the electrons would have to move faster than light to resist the gravity, the white dwarf must explode as a supernova. This limit is about 2.4 MSun.

b) If mass of the white dwarf becomes so great that the electrons would have to move faster than light to resist the gravity, the white dwarf must collapse into a neutron star. This limit is about 1.4 MSun.

Which of the following statements about electron degeneracy pressure and neutron degeneracy pressure is true?

a) Electron degeneracy pressure is the main source of pressure in white dwarfs, while neutron degeneracy pressure is the main source of pressure in neutron stars.
b) Both electron degeneracy pressure and neutron degeneracy pressure help govern the internal structure of a main-sequence star.
c) In a black hole, the pressure coming from neutron degeneracy pressure is slightly greater than that coming from electron degeneracy pressure.
d) The life of a white dwarf is an ongoing battle between electron degeneracy pressure and neutron degeneracy pressure.

a) Electron degeneracy pressure is the main source of pressure in white dwarfs, while neutron degeneracy pressure is the main source of pressure in neutron stars.

Which of these neutron stars must have had its angular momentum changed by a binary companion?

a) a pulsar that pulses 600 times per second
b) a pulsar that pulses 30 times per second
c) a neutron star that does not pulse at all

a) a pulsar that pulses 600 times per second

Part A:
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?

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

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

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

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

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

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

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

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

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

Part A: b) Time runs increasingly slower as the rocket approaches the black hole. Part B: a) slows down as it approaches the event horizon and never actually crosses the event horizon Part C: b) Its light will become so redshifted that it will be undetectable. Part D: b) at a constant, normal rate as you approach the event horizon Part E: c) accelerate as you fall and cross the event horizon completely unhindered

the characteristics of a White dwarf and a Neutron Star

White Dwarf: – emits most strongly in visible and ultraviolt -may be in a binary system that undergoes nova explosions -may be surrounded by a planetary nebula Neutron Star: -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 -may be surrounded by a supernova remant

observational characteristics of a Neutron Star only, Black hole only, and Both neutron stars and black holes

Neutron Star only: – may emit rapid pulses of radio waves -may be in a binary system that undergoes X-ray bursts Black Hole only: is detectable if it is accreting gas from other objects -can have a mass of 10 solar masses Both neutron stars and black holes: -may be located in an X-ray binary -may be surrounded by a supernova remnant

Where do gamma-ray bursts tend to come from?

a) extremely distant galaxies
b) neutron stars in our galaxy
c) binary systems that also emit X-ray bursts

a) extremely distant galaxies

Which of these black holes exerts the weakest tidal force on an object near its event horizon?

a) a 10MSun black hole
b) a 10^6MSun black hole
c) a 100MSun black hole

b) a 10^6MSun black hole

What would happen if the Sun suddenly became a black hole without changing its mass?

a) Earth would remain in the same orbit.
b) Earth would gradually spiral into the black hole.
c )The black hole would quickly suck in Earth.

a) Earth would remain in the same orbit.

The Schwarzschild radius of a black hole depends on ________.

a) both the mass and chemical composition of the black hole
b) the way in which the black hole formed
c) only the mass of the black hole
d) the observationally measured radius of the black hole

c) only the mass of the black hole

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

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

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

A teaspoonful of white dwarf material on Earth would weigh

a) a few tons.
b) about the same as Earth.
c) a few million tons.
d) the same as a teaspoonful of Earth-like material.
e) about the same as Mt. Everest.

a) a few tons.

What is the ultimate fate of an isolated white dwarf?

a) As gravity overwhelms the electron degeneracy pressure, it will explode as a supernova.
b) The electron degeneracy pressure will eventually overwhelm gravity and the white dwarf will slowly evaporate.
c )As gravity overwhelms the electron degeneracy pressure, it will explode as a nova.
d) As gravity overwhelms the electron degeneracy pressure, it will become a neutron star.
e )It will cool down and become a cold black dwarf.

e )It will cool down and become a cold black dwarf.

What is the upper limit to the mass of a white dwarf?

a) 1.4 solar masses
b) There is no upper limit.
c) 2 solar masses
d) There is an upper limit, but we do not yet know what it is.
e) 1 solar mass

a) 1.4 solar masses

Observationally, how can we tell the difference between a white-dwarf supernova and a massive-star supernova?

a) A massive-star supernova happens only once, while a white-dwarf supernova can repeat periodically.
b) The light of a white-dwarf supernova fades steadily, while the light of a massive-star supernova brightens for many weeks.
c) The spectrum of a massive-star supernova shows prominent hydrogen lines, while the spectrum of a white-dwarf supernova does not.
d) A massive-star supernova is brighter than a white-dwarf supernova.
e) We cannot yet tell the difference between a massive-star supernova and a white-dwarf supernova.

c) The spectrum of a massive-star supernova shows prominent hydrogen lines, while the spectrum of a white-dwarf supernova does not.

Our Sun will likely undergo a nova event in about 5 billion years.

True
False

false

What is the ultimate fate of an isolated pulsar?

a) As gravity overwhelms the neutron degeneracy pressure, it will explode as a supernova.
b) The neutron degeneracy pressure will eventually overwhelm gravity and the pulsar will slowly evaporate.
c) It will spin ever faster, becoming a millisecond pulsar.
d) It will slow down, the magnetic field will weaken, and it will become invisible.
e) As gravity overwhelms the neutron degeneracy pressure, it will become a white dwarf.

d) It will slow down, the magnetic field will weaken, and it will become invisible.

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

True
False

false

Which of the following statements about black holes is not true?

a) If we watch a clock fall toward a black hole, we will see it tick slower and slower as it falls nearer to the black hole.
b) A black hole is truly a hole in spacetime, through which we could leave the observable universe.
c) If the Sun magically disappeared and was replaced by a black hole of the same mass, Earth would soon be sucked into the black hole.
d) If you watch someone else fall into a black hole, you will never see him or her cross the event horizon. However, he or she will fade from view as the light he or she emits (or reflects) becomes more and more redshifted.
e) If you fell into a black hole, you would experience time to be running normally as you plunged rapidly across the event horizon.

c) If the Sun magically disappeared and was replaced by a black hole of the same mass, Earth would soon be sucked into the black hole.

When we see X rays from an accretion disk in a binary system, we can’t immediately tell whether the accretion disk surrounds a neutron star or a black hole. Suppose we then observe each of the following phenomena in this system. Which one would force us to immediately rule out the possibility of a black hole?

a) spectral lines from the companion star that alternately shift to shorter and longer wavelengths
b) sudden, intense X-ray bursts
c) visible and ultraviolet light from the companion star
d) bright X-ray emission that varies on a time scale of a few hours

b) sudden, intense X-ray bursts

A white dwarf is _________.

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

b) what most stars become when they die

A typical white dwarf is _________.

a) as massive as the Sun but only about as large in size as Jupiter
b) about the same size and mass as the Sun but much hotter
d) as massive as the Sun but only about as large in size as Earth
e) as large in diameter as the Sun but only about as massive as Earth

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

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

a) as much as an average person
b) as much as the entire Earth
c) about 5 pounds
d) as much as a truck

d) as much as a truck

The maximum mass of a white dwarf is _________.

a) limitless; there is no theoretical limit to the maximum mass of a white dwarf
b) about 1.4 times the mass of our Sun
c) about the mass of our Sun
d) about three times the mass of our Sun

b) about 1.4 times the mass of our Sun

What is an accretion disk?

a) any flattened disk in space, such as the disk of the Milky Way Galaxy
b) a disk of hot gas swirling rapidly around a white dwarf, neutron star, or black hole
c) a stream of gas flowing from one star to its binary companion star
d) a disk of material found around every white dwarf in the Milky Way Galaxy

b) a disk of hot gas swirling rapidly around a white dwarf, neutron star, or black hole

According to our modern understanding, what is a nova?

a) the sudden formation of a new star in the sky
b) a rapidly spinning neutron star
c) the explosion of a massive star at the end of its life
d) an explosion on the surface of a white dwarf in a close binary system

d) an explosion on the surface of a white dwarf in a close binary system

Suppose that a white dwarf gains enough mass to reach the 1.4 solar-mass limit?

a) The white dwarf will undergo a nova explosion.
b) The white dwarf will collapse to become a black hole.
c) The white dwarf will collapse in size, becoming a neutron star.
d) The white dwarf will explode completely as a white dwarf supernova.

d) The white dwarf will explode completely as a white dwarf supernova.

A neutron star is _________.

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

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

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

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

b) a small asteroid (10 km in diameter)

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

a) about 50 pounds
b) about as much as a truck
c) about as much as a large mountain
d) as much as the entire Earth

c) about as much as a large mountain

Pulsars are thought to be _________.

a) accreting black holes
b) unstable high-mass stars
d) rapidly rotating neutron stars
e) accreting white dwarfs

d) rapidly rotating neutron stars

How is an X-ray burst (in an X-ray binary system) similar to a nova?

a) Both typically recur every few hours to every few days.
b) Both are thought to involve fusion of hydrogen into helium.
c) Both result in the complete destruction of their host stars.
d) Both involve explosions on the surface of stellar corpse

d) Both involve explosions on the surface of stellar corpse

What is the basic definition of a black hole?

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

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

Based on current understanding, the minimum mass of a black hole that forms during a massive star supernova is roughly _________.

a) 3 solar masses
b) 1.4 solar masses
c) 0.5 solar masses
d) 10 solar masses

a) 3 solar masses

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

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

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

Imagine that our Sun were magically and suddenly replaced by a black hole of the same mass (1 solar mass). What would happen to Earth in its orbit?

a) Earth would orbit faster but at the same distance.
b) Nothing. Earth’s orbit would remain the same.
c) Earth would almost instantly be sucked into oblivion in the black hole.
d) Earth would slowly spiral inward until it settled into an orbit about the size of Mercury’s current orbit.

b) Nothing. Earth’s orbit would remain the same.

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

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 edge of the black hole, where one could leave the observable universe.
c) 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.
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.

What makes us think that the star system Cygnus X-1 contains a black hole?

a) No light is emitted from this star system, so it must contain a black hole.
b) The fact that we see strong X-ray emission tells us that the system must contain a black hole.
c) Cygnus X-1 is a powerful X-ray burster, so it must contain a black hole.
d) It emits X-ray characteristics of an accretion disk, but the unseen star in the system is too massive to be a neutron star.

d) It emits X-ray characteristics of an accretion disk, but the unseen star in the system is too massive to be a neutron star

The Schwarzschild radius of a black hole depends on ________.

a) only the mass of the black hole
b) the way in which the black hole formed
c) both the mass and chemical composition of the black hole
d) the observationally measured radius of the black hole

a) only the mass of the black hole

Evidence indicates that many gamma ray bursts are produced by __________.

a) the central black hole of the Milky Way Galaxy
b) white dwarf supernovas in distant galaxies.
c) supernovas of massive stars in distant galaxies
d) the same types of close binary systems that produce X-ray bursts

c) supernovas of massive stars in distant galaxies

Which of the following statements about electron degeneracy pressure and neutron degeneracy pressure is true?

a) In a black hole, the pressure coming from neutron degeneracy pressure is slightly greater than that coming from electron degeneracy pressure.
b) The life of a white dwarf is an ongoing battle between electron degeneracy pressure and neutron degeneracy pressure.
c) Electron degeneracy pressure is the main source of pressure in white dwarfs, whereas neutron degeneracy pressure is the main source of pressure in neutron stars.
d) Both electron degeneracy pressure and neutron degeneracy pressure help govern the internal structure of a main-sequence star.

c) Electron degeneracy pressure is the main source of pressure in white dwarfs, whereas neutron degeneracy pressure is the main source of pressure in neutron stars.

Suppose two neutron stars are closely orbiting one another. What do scientists suspect will eventually happen to them, and why?

a) Their orbits will gradually grow larger because of the centrifugal force involved as they circle around each other.
b) Their orbits will spiral inward until the two neutron stars merge because of energy lost through gravitational waves.
c) Their orbits will spiral inward as a result of friction with surrounding as until all the gas clears, after which their orbits will remain stable.
d) The orbits would remain stable unless there were a third star orbiting along with them.

b) Their orbits will spiral inward until the two neutron stars merge because of energy lost through gravitational waves.