Exam 3
2) Since all stars begin their lives with the same basic composition,
what characteristic most determines how they will differ?
A)
location where they are formed
B) time they are formed
C)
luminosity they are formed with
D) mass they are formed with
E) color they are formed with
Answer: D
3) What are the standard units for luminosity?
A) watts
B) joules
C) Newtons
D) kilograms
E) watts per second
Answer: A
4) A star's luminosity is the
A) apparent brightness of the
star in our sky.
B) surface temperature of the star.
C)
lifetime of the star.
D) total amount of light that the star
will radiate over its entire lifetime.
E) total amount of light
that the star radiates each second.
Answer: E
5) What are the standard units for apparent brightness?
A)
watts
B) joules
C) Newtons
D) watts per second
E) watts per square meter
Answer: E
6) If the distance between us and a star is doubled, with everything
else remaining the same, the luminosity
A) is decreased by a
factor of four, and the apparent brightness is decreased by a factor
of four.
B) is decreased by a factor of two, and the apparent
brightness is decreased by a factor of two.
C) remains the same,
but the apparent brightness is decreased by a factor of two.
D)
remains the same, but the apparent brightness is decreased by a factor
of four.
E) is decreased by a factor of four, but the apparent
brightness remains the same.
Answer: D
7) Which of the following correctly states the luminosity-distance
formula?
A) luminosity = (Apparent brightness)/4π × (distance)^2
B) apparent brightness = (luminosity)/4π × (distance)^2
C)
apparent brightness = luminosity × 4π × (distance)^2
D) distance
= (luminosity)/4π × (distance)^2
Answer: B
8) Why do astronomers often measure the visible-light apparent
brightness instead of the total apparent brightness of a star?
A) All stars put out most of their light in the visible range of
the spectrum.
B) In order to measure the total apparent
brightness of a star, you must measure its brightness in all
wavelengths, and this is difficult to do. The only wavelengths you can
measure from the surface of Earth are visible and radio wavelengths.
C) Most stars do not put out light in other ranges of the
spectrum.
D) They are identical for most stars.
E)
Astronomers are lazy.
Answer: B
9) Suppose you measure the parallax angle for a particular star to be
0.1 arcsecond. The distance to this star is
A) 10 light-years.
B) 10 parsecs.
C) 0.1 light-year.
D) 0.1 parsec.
E) impossible to determine.
Answer: B 1/arcsecond
11) The most distant stars we can measure stellar parallax for are
approximately
A) 50 parsecs away.
B) 500 parsecs away.
C) 5,000 parsecs away.
D) halfway across the Milky Way
Galaxy.
E) in the Andromeda Galaxy.
Answer: B
2) Which of the following statements about apparent and absolute
magnitudes is true?
A) The magnitude system that we use now is
based on a system used by the ancient Greeks over 2,000 years ago that
classified stars by how bright they appeared.
B) A star with
apparent magnitude 1 is brighter than one with apparent magnitude 2.
C) The absolute magnitude of a star is another measure of its
luminosity.
D) A star's absolute magnitude is the apparent
magnitude it would have if it were at a distance of 10 parsecs from
Earth.
E) All of the above are true.
Answer: E
13) The spectral sequence sorts stars according to
A) mass.
B) surface temperature.
C) luminosity.
D) core
temperature.
E) radius.
Answer: B
14) The spectral sequence in order of decreasing temperature is
A) OFBAGKM.
B) OBAGFKM.
C) OBAFGKM.
D)
ABFGKMO.
E) BAGFKMO.
Answer: C
15) Why is the spectral sequence of stars not alphabetical?
A)
The letters refer to the initials of the original discovers.
B)
The original alphabetical labeling did not correspond to surface
temperature and thus had to be reordered.
C) They were chosen to
fit a mnemonic.
D) Because there is still uncertainty over what
generates the energy in stellar cores.
E) Because it refers to
stellar masses and these were difficult to measure accurately.
Answer: B
16) Which of the following statements about spectral types of stars
is true?
A) The spectral type of a star can be used to determine
its surface temperature.
B) The spectral type of a star can be
used to determine its color.
C) A star with spectral type A is
cooler than a star with spectral type B.
D) A star with spectral
type F2 is hotter than a star with spectral type F3.
E) All of
the above are true.
Answer: E
17) Which of the following persons reorganized the spectral
classification scheme into the one we use today and personally
classified over 400,000 stars?
A) Annie Jump Cannon
B)
Williamina Fleming
C) Cecilia Payne-Gaposchkin
D) Henry
Draper
E) Edward Pickering
Answer: A
18) Which of the following persons used the ideas of quantum
mechanics to describe why the spectral classification scheme is in
order of decreasing temperature?
A) Annie Jump Cannon
B)
Williamina Fleming
C) Cecilia Payne-Gaposchkin
D) Henry
Draper
E) Edward Pickering
Answer: C
19) Suppose you see two main-sequence stars of the same spectral
type. Star 1 is dimmer in apparent brightness than Star 2 by a factor
of 100. What can you conclude? (Neglect any effects that might be
caused by interstellar dust and gas.)
A) Without first knowing
the distances to these stars, you cannot draw any conclusions about
how their true luminosities compare to each other.
B) The
luminosity of Star 1 is a factor of 100 less than the luminosity of
Star 2.
C) Star 1 is 100 times more distant than Star 2.
D) Star 1 is 100 times nearer than Star 2.
E) Star 1 is 10
times more distant than Star 2.
Answer: E
20) Which of the following terms is given to a pair of stars that
appear to change positions in the sky, indicating that they are
orbiting one another?
A) visual binary
B) eclipsing binary
C) spectroscopic binary
D) double star
E) none of
the above
Answer: A
22) Which of the following best describes the axes of a
Hertzsprung-Russell (H-R) diagram?
A) surface temperature on the
horizontal axis and luminosity on the vertical axis
B) mass on
the horizontal axis and luminosity on the vertical axis
C)
surface temperature on the horizontal axis and radius on the vertical
axis
D) mass on the horizontal axis and stellar age on the
vertical axis
E) interior temperature on the horizontal axis and
mass on the vertical axis
Answer: A
23) On a Hertzsprung-Russell diagram, where would we find stars that
are cool and dim?
A) upper right
B) lower right
C)
upper left
D) lower left
Answer: B
24) On a Hertzsprung-Russell diagram, where would we find stars that
are cool and luminous?
A) upper right
B) lower right
C) upper left
D) lower left
Answer: A
25) On a Hertzsprung-Russell diagram, where would we find stars that
have the largest radii?
A) upper right
B) lower right
C) upper left
D) lower left
Answer: A
26) On a Hertzsprung-Russell diagram, where on the main sequence
would we find stars that have the greatest mass?
A) upper right
B) lower right
C) upper left
D) lower left
Answer: C
27) On a Hertzsprung-Russell diagram, where would we find red giant
stars?
A) upper right
B) lower right
C) upper left
D) lower left
Answer: A
28) On a Hertzsprung-Russell diagram, where would we find white
dwarfs?
A) upper right
B) lower right
C) upper left
D) lower left
Answer: D
29) You observe a star in the disk of the Milky Way, and you want to
plot the star on an H-R diagram. You will need to determine all of the
following, except the
A) spectral type of the star.
B)
distance to the star.
C) apparent brightness of the star in our
sky.
D) rotation rate of the star.
Answer: D
30) On the main sequence, stars obtain their energy
A) from
chemical reactions.
B) from gravitational contraction.
C)
by converting hydrogen to helium.
D) by converting helium to
carbon, nitrogen, and oxygen.
E) from nuclear fission.
Answer: C
31) The faintest star visible to the naked eye has an apparent visual
magnitude of about
A) 10.
B) 6.
C) 1.
D) 0.
E) -6.
Answer: B the higher the number the fainter the star will appear
32) Which of the following is the most common type of main-sequence
star?
A) an O star
B) an A star
C) an F star
D) an M star
E) a G star
Answer: D
33) Which of the following characteristics of stars has the greatest
range in values?
A) mass
B) radius
C) core
temperature
D) surface temperature
E) luminosity
Answer: E
34) A star of spectral type O lives approximately how long on the
main sequence?
A) 1,000 years
B) 10,000 years
C) 10
million years
D) 100 million years
E) 1 billion years
Answer: C
35) A star of spectral type G lives approximately how long on the
main sequence?
A) 1,000 years
B) 10,000 years
C) 1
million years
D) 100 million years
E) 10 billion years
Answer: E
36) Which of the following is true about low-mass stars compared to
high-mass stars?
A) Low-mass stars are cooler and less luminous
than high-mass stars.
B) Low-mass stars are hotter and more
luminous than high-mass stars.
C) Low-mass stars are cooler but
more luminous than high-mass stars.
D) Low-mass stars are hotter
but less luminous than high-mass stars.
E) Low-mass stars have
the same temperature and luminosity as high-mass stars.
Answer: A
37) Which of the following luminosity classes refers to stars on the
main sequence?
A) I
B) II
C) III
D) IV
E) V
Answer: E
38) In a pulsating variable star, which characteristic of the star
changes dramatically with time?
A) mass
B) core
temperature
C) luminosity
D) energy-generation process
E) rotation rate
Answer: C
39) Why are Cepheid variables so important for measuring distances in
astronomy?
A) They all have the same luminosity.
B) They
all have the same period.
C) Their luminosity can be inferred
from their period.
D) They are close enough to have a detectable
parallax.
E) They are circumpolar like Polaris, the North Star.
Answer: C
40) Which of the following statements about an open cluster is true?
A) All stars in the cluster are approximately the same color.
B) All stars in the cluster are approximately the same age.
C) All stars in the cluster have approximately the same mass.
D) All stars in the cluster will evolve similarly.
E)
There is an approximately equal number of all types of stars in the cluster.
Answer: B
41) Which of the following statements about a globular cluster is
true?
A) All stars in the cluster are approximately at the same
stage in evolution.
B) Most of the stars in the cluster are
younger than 10 billion years old.
C) Most stars in the cluster
are yellow or reddish in color.
D) All stars in the cluster have
approximately the same mass.
E) There is an approximately equal
number of all types of stars in the cluster.
Answer: C
42) Cluster ages can be determined from
A) main sequence
fitting.
B) main sequence turnoff.
C) pulsating variable
stars.
D) spectroscopic binaries.
E) visual binaries.
Answer: B
43) In order to understand star clusters, we need to be able to
estimate their ages. What technique do scientists use for this?
A) radioisotope dating
B) counting the planets that have
formed around the largest stars
C) finding the main-sequence
turnoff point of the stars
D) calculating orbital parameters
using Kepler's Laws
E) measuring its parallax
Answer: C
1) The apparent brightness of a star depends only on its luminosity.
Answer: FALSE
2) If the distance between us and a star is doubled, the apparent brightness is decreased by a factor of four.
Answer: TRUE
3) The more distant a star, the smaller its parallax.
Answer: TRUE
4) We can measure stellar parallax for most stars in our galaxy.
Answer: FALSE
5) Spectral type, surface temperature, and color all describe the same basic characteristic of a star.
Answer: TRUE
6) Some stars are cool enough to have molecules in their atmosphere.
Answer: TRUE
7) We can measure the radii of stars in an eclipsing binary system, in addition to the masses.
Answer: TRUE
8) Two stars have the same spectral type. Star X is in luminosity class III, while Star Y is in luminosity class V. Therefore, Star X is larger in radius than Star Y.
Answer: TRUE
9) Two stars have the same luminosity. Star X is spectral type F, while Star Y is spectral type K. Therefore, Star X is larger in radius than Star Y.
Answer: FALSE
10) Two stars both lie on the main sequence. Star X is spectral type A, while Star Y is spectral type G. Therefore, Star X is more massive than Star Y.
Answer: TRUE
11) A 10-solar-mass star is about ten times more luminous than a 1-solar-mass star.
Answer: FALSE
12) Most stars on the main sequence fuse hydrogen into helium in their cores, but some do not.
Answer: FALSE
13) All stars spend approximately the same amount of time on the main sequence.
Answer: FALSE
1) What is the approximate chemical composition (by mass) with which
all stars are born?
A) three quarters hydrogen, one quarter
helium, no more than 2% heavier elements
B) half hydrogen and
half helium
C) 98% hydrogen, 2% helium
D) 95% hydrogen, 4%
helium, no more than 1% heavier elements
Answer: A
2) The total amount of power (in watts, for example) that a star
radiates into space is called its
A) apparent brightness.
B)
absolute magnitude.
C) luminosity.
D) flux.
Answer: C
3) According to the inverse square law of light, how will the
apparent brightness of an object change if its distance to us triples?
A) Its apparent brightness will increase by a factor of 9.
B) Its apparent brightness will decrease by a factor of 9.
C) Its apparent brightness will increase by a factor of 3.
D) Its apparent brightness will decrease by a factor of 3.
Answer: B
4) Assuming that we can measure the apparent brightness of a star,
what does the inverse square law for light allow us to do?
A)
Determine both the star's distance and luminosity from its apparent
brightness.
B) Determine the distance to the star from its
apparent brightness.
C) Calculate the star's luminosity if we
know its distance, or calculate its distance if we know its
luminosity.
D) Calculate the star's surface temperature if we
know either its luminosity or its distance.
Answer: C
5) If Star A is closer to us than Star B, then Star A's parallax
angle is
A) smaller than that of Star B.
B) larger than
that of Star B.
C) hotter than that of Star B.
D) fewer
parsecs than that of Star B.
Answer: B
) Ten parsecs is about
A) 150 million kilometers.
B) 10,000
seconds.
C) 10 parallax seconds of angle.
D) 32.6 light-years.
Answer: D
7) Star A has an apparent magnitude of 3 and Star B has an apparent
magnitude of 5. Which star is brighter in our sky?
A) Star A
B) Star B
C) The two stars have the same brightness in our
sky, but Star A is closer to us than Star B.
D) There is not
enough information to answer the question.
Answer: A
9) Our Sun is a star of spectral type
A) F.
B) M.
C)
G.
D) S.
Answer: C
10) Astronomers can measure a star's mass in only certain cases.
Which one of the following cases might allow astronomers to measure a
star's mass?
A) The star is a member of a binary star system.
B) The star is of spectral type G.
C) The star is of
spectral type A.
D) We know the star's luminosity and distance.
Answer: A
11) Which of the following terms is given to a pair of stars that we
can determine are orbiting each other only by measuring their periodic
Doppler shifts?
A) eclipsing binary
B) spectroscopic
binary
C) visual binary
D) double star
Answer: B
12) The axes on a Hertzsprung-Russell (H-R) diagram represent
A) mass and luminosity.
B) luminosity and surface
temperature.
C) luminosity and apparent brightness.
D) mass
and radius.
Answer: B
13) On an H-R diagram, stellar radii
A) are greatest in the
lower left and least in the upper right.
B) decrease from left to
right.
C) are impossible to determine.
D) increase
diagonally from the lower left to the upper right.
Answer: D
14) On an H-R diagram, stellar masses
A) can be determined for
main-sequence stars but not for other types of stars.
B) are
greatest in the lower left and least in the upper right.
C)
decrease from upper left to lower right.
D) are impossible to determine.
Answer: A
16) How is the lifetime of a star related to its mass?
A) More
massive stars live slightly shorter lives than less massive stars.
B) More massive stars live much longer lives than less massive
stars.
C) More massive stars live much shorter lives than less
massive stars.
D) More massive stars live slightly longer lives
than less massive stars.
Answer: C
17) Each choice below lists a spectral type and luminosity class for
a star. Which one is a red supergiant?
A) spectral type M1,
luminosity class V
B) spectral type O9, luminosity class I
C) spectral type G2, luminosity class V
D) spectral type
M2, luminosity class I
Answer: D
18) What is the common trait of all main-sequence stars?
A)
They are in the final stage of their lives.
B) They generate
energy through hydrogen fusion in their core.
C) They are all
spectral type G.
D) They all have approximately the same mass.
Answer: B
19) Suppose our Sun were suddenly replaced by a supergiant star.
Which of the following would be true?
A) Earth would be inside
the supergiant.
B) The supergiant's surface temperature would be
much hotter than the surface temperature of our Sun.
C) Earth
would fly off into interstellar space.
D) The supergiant would
appear as large as the full Moon in our sky.
Answer: A
20) What is a white dwarf?
A) It is a main-sequence star of
spectral type F, which tends to look white in color.
B) It is
the remains of a star that ran out of fuel for nuclear fusion.
C) It is a type of star that produces energy by gravitational
contraction.
D) It is a star that follows a period-luminosity relation.
Answer: B
21) Which of the following statements comparing open and globular
star clusters is not true?
A) Open clusters are found only in
the disk of the galaxy while globular clusters may be found both in
the disk and the halo of the galaxy.
B) Stars in open clusters
are relatively young while stars in globular clusters are very old.
C) Open and globular clusters each typically contain a few
hundred stars.
D) For both open and globular clusters, we can
assume that all the stars in a particular cluster are about the same age.
Answer: C
22) What do we mean by the main-sequence turnoff point of a star
cluster, and what does it tell us?
A) It is the point in a star
cluster beyond which main-sequence stars are not found, and it tells
us the cluster's distance.
B) It is the spectral type of the
hottest main-sequence star in a star cluster, and it tells us the
cluster's age.
C) It is the luminosity class of the largest star
in a star cluster, and it tells us the cluster's age.
D) It is
the mass of the most massive star in the star cluster, and it tells us
the cluster's size.
Answer: B
1) All stars are born with the same basic composition, yet stars can
look quite different from one another. Which two factors primarily
determine the characteristics of a star?
A) its mass and its
stage of life
B) its apparent brightness and its distance
C) its age and its location in the galaxy
D) its mass and
its surface temperature
E) its apparent brightness and its luminosity
Answer: A
3) Star A is identical to Star B, except that Star A is twice as far
from us as Star B. Therefore
A) both stars have the same
luminosity, but the apparent brightness of Star B is twice that of
Star A.
B) both stars have the same apparent brightness, but the
luminosity of Star B is four times that of Star A.
C) both stars
have the same luminosity, but the apparent brightness of Star A is
four times that of Star B.
D) both stars have the same
luminosity, but the apparent brightness of Star B is four times that
of Star A.
Answer: D
4) A star with a parallax angle of 1/20 arcsecond is
A) 20
light-years away.
B) 1/20 parsec away.
C) 20 parsecs
away.
D) 10 parsecs away.
Answer: C
5) The star Vega has an absolute magnitude of about 4 and an apparent
magnitude of about 0. Based on the definitions of absolute and
apparent magnitude, we can conclude that
A) Vega is nearer than
10 parsecs from Earth.
B) Vega has a parallax angle of 1/10
arcsecond.
C) Vega's luminosity is less than that of our
Sun.
D) Vega's surface temperature is cooler than the Sun.
Answer: A
6) Which of the following statements about spectral types of stars is
not generally true?
A) The spectral type of a star can be used
to determine its surface temperature.
B) The spectral type of a
star can be used to determine its distance.
C) The spectral type
of a star can be used to determine its color.
D) The spectral
type of a star can be determined by identifying lines in its spectrum.
Answer: B
7) Sirius is a star with spectral type A star and Rigel is a star
with spectral type B star. What can we conclude?
A) Rigel has a
higher core temperature than Sirius.
B) Sirius has a higher core
temperature than Rigel.
C) Rigel has a higher surface
temperature than Sirius.
D) Sirius has a higher surface
temperature than Rigel.
Answer: C
8) To calculate the masses of stars in a binary system, we must
measure their
A) spectral types and distance from Earth.
B)
absolute magnitudes and luminosities.
C) luminosities and
distance from Earth.
D) orbital period and average orbital distance.
Answer: D
9) Careful measurements reveal that a star maintains a steady
apparent brightness at most times, except that at precise intervals of
73 hours the star becomes dimmer for about 2 hours. The most likely
explanation is that
A) the star is a Cepheid variable.
B)
the star is a member of an eclipsing binary star system.
C) the
star is periodically ejecting gas into space, every 73 hours.
D)
the star is a white dwarf.
Answer: B
10) Which group represents stars that are cool and dim?
A) A
B) B
C) C
D) D
E) E
Answer: D
11) Which group represents stars of the largest radii?
A) A
B) B
C) C
D) D
E) E
Answer: E
12) Which group represents the most common type of stars?
A) A
B) B
C) C
D) D
E) E
Answer: D
13) Which group represents stars that are extremely bright and emit
most of their radiation as ultraviolet light?
A) A
B) B
C) C
D) D
E) E
Answer: C
14) Which group represents stars with the longest main-sequence
lifetimes?
A) A
B) B
C) C
D) D
E) E
Answer: D
15) Which group represents stars fusing hydrogen in their cores?
A) A
B) B
C) C
D) D
E) E
Answer: A
16) Which group represents stars that have no ongoing nuclear fusion?
A) A
B) B
C) C
D) D
E) E
Answer: B
17) You observe a star and you want to plot it on an H-R diagram. You
will need to measure all of the following, except the star's
A)
mass.
B) distance.
C) apparent brightness.
D) spectral type.
Answer: A
18) The approximate main-sequence lifetime of a star of spectral type
O is
A) 10,000 years.
B) 3 million years.
C) 300
million years.
D) 10 billion years.
Answer: B
19) How did astronomers discover the relationship between spectral
type and mass for main-sequence stars?
A) by using computer
models of hydrogen fusion and stellar structure
B) by measuring
stellar radii with very powerful telescopes
C) by comparing
stars with the same spectral type but different luminosities
D)
by measuring the masses and spectral types of main-sequence stars in
binary systems
Answer: D
20) The choices below each describe the appearance of an H-R diagram
for a different star cluster. Which cluster is the youngest?
A)
The diagram shows main-sequence stars of spectral types G, K, and M,
along with numerous giants and white dwarfs.
B) The diagram
shows main-sequence stars of all the spectral types except O and B,
along with a few giants and supergiants.
C) The diagram shows
main-sequence stars of every spectral type except O, along with a few
giants and supergiants.
D) The diagram shows no main-sequence
stars at all, but it has numerous supergiants and white dwarfs.
Answer: C
21) The choices below each describe the appearance of an H-R diagram
for a different star cluster. Which cluster is most likely to be
located in the halo of our galaxy?
A) The diagram shows
main-sequence stars of every spectral type except O, along with a few
giants and supergiants.
B) The diagram shows main-sequence stars
of spectral types G, K, and M, along with numerous giants and white
dwarfs.
C) The diagram shows main-sequence stars of all the
spectral types except O and B, along with a few giants and
supergiants.
D) The diagram shows no main-sequence stars at all,
but it has numerous supergiants and white dwarfs.
Answer: B
1) Astronomers estimate that new stars form in our galaxy at the rate
of about
A) one per year.
B) a few (2-3) per year.
C) ten per year.
D) 20-30 per year.
E) 100 per year.
Answer: B
2) 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) 70% Hydrogen, 20% Helium,
10% heavier elements.
D) 50% Hydrogen, 50% Helium.
E) 50%
Hydrogen, 30% Helium, 20% heavier elements.
Answer: B
3) What percentage of a molecular cloud's mass is interstellar dust?
A) 1%
B) 2%
C) 28%
D) 50%
E) 1-50%,
depending on the mass of the molecular cloud
Answer: A
4) The typical density and temperature of molecular clouds are
A) 100 molecules per cubic centimeter, 10-30 Kelvin.
B)
300 molecules per cubic centimeter, 10-30 Kelvin.
C) 1000
molecules per cubic centimeter, 10-30 Kelvin.
D) 100 molecules
per cubic centimeter, 100-300 Kelvin.
E) 300 molecules per cubic
centimeter, 100-300 Kelvin.
Answer: B
6) The typical size of an interstellar dust grain is
A) 1
angstrom.
B) 1 nanometer.
C) 1 micrometer.
D) 1
millimeter.
E) 1 centimeter.
Answer: C
7) What is interstellar reddening?
A) Interstellar dust absorbs
more red light than blue light, making stars appear redder than their
true color.
B) Interstellar dust absorbs more red light than
blue light, making stars appear bluer than their true color.
C)
Interstellar dust absorbs more blue light than red light, making stars
appear redder than their true color.
D) Interstellar dust
absorbs more blue light than red light, making stars appear bluer than
their true color.
E) The spectral line shift due to a star's
motion through the interstellar medium.
Answer: C
8) If you wanted to observe stars behind a molecular cloud, in what
wavelength of light would you most likely observe?
A)
ultraviolet
B) visible
C) infrared
D) X-ray
E) gamma-ray
Answer: C
9) What happens to the visible radiation produced by new stars within
a molecular cloud?
A) It escapes the cloud completely.
B)
It is absorbed by dust grains and heats up the cloud.
C) It is
reflected back onto the protostar, heating it up further.
D) The
blue light is absorbed and the red light transmitted.
E) It
shoots out in bright jets.
Answer: B
10) The thermal pressure of a gas depends on
A) density only.
B) temperature only.
C) density and temperature.
D)
composition.
E) gravity.
Answer: C
11) The gravitational force in a molecular cloud depends on
A)
density only.
B) temperature only.
C) density and
temperature.
D) composition.
E) thermal pressure.
Answer: A
12) What prevents the pressure from increasing as a cloud contracts
due to its gravity?
A) As the cloud becomes denser, gravity
becomes stronger and overcomes the pressure buildup.
B) The
pressure is transferred from the center of the cloud to its outer
edges where it can dissipate.
C) Thermal energy is converted to
radiative energy via molecular collisions and released as photons.
D) Excess pressure is released in jets of material from the
young stars.
E) Once the cloud reaches a critical density, the
pressure becomes degenerate and independent of temperature.
Answer: C
13) Calculations show that gravity begins to overcome thermal
pressure in clouds that are
A) less massive than the Sun.
B) more massive than the Sun.
C) more massive than ten
times the Sun.
D) more massive than a hundred times the Sun.
E) more massive than a thousand times the Sun.
Answer: D
14) What property of a molecular cloud does not counteract
gravitational contraction?
A) thermal pressure
B)
turbulent motions
C) magnetic fields
D) fragmentation
Answer: D
15) How do astronomers infer the presence of magnetic fields in
molecular clouds?
A) by measuring the amount of interstellar
reddening
B) by measuring the Doppler shifts of emission lines
from gas clumps in the cloud
C) by measuring the infrared light
emitted by the cloud
D) by measuring the polarization of
starlight passing through the cloud
E) by measuring the amount
by which gravity is reduced
Answer: D
16) What is the likely reason that we cannot find any examples of the
first generation stars?
A) The first generation stars are too
faint to be visible now.
B) The first generation stars formed
such a long time ago that the light from them has not yet had time to
reach us.
C) The first generation stars were all very massive
and exploded as supernova.
D) The first generation stars formed
with only H and He and therefore have no spectral features.
E)
We do not know how the first generation stars were formed.
Answer: C
17) Why do we think the first generation of stars would be different
from stars born today?
A) Without heavy elements, the clouds
could not reach as low a temperature as today and had to be more
massive to collapse.
B) Without heavy elements, the nuclear
reactions at the center of the stars would be very different.
C)
Without heavy elements, there was no dust in the clouds and they
collapsed faster.
D) The Universe was much denser when the first
stars were born.
E) There were no galaxies when the first stars
were born.
Answer: A
18) What is the minimum temperature for a cloud to excite emission
lines from H2?
A) 10 K
B) 30 K
C) 100 K
D) 300
K
E) 1000 K
Answer: C
19) When is thermal energy trapped in the dense center of a cloud?
A) when the gravity becomes so strong that photons cannot escape
B) when excited molecules collide with other molecules before
they can release a photon
C) when the cloud becomes so hot and
dense that nuclear fusion begins
D) when magnetic fields trap
the radiation
E) when the cloud cools down so much that less
light escapes than is produced by contraction
Answer: B
20) What happens to the rotation of a molecular cloud as it collapses
to form a star?
A) The rotation rate remains the same and
results in stellar rotation.
B) The rotation dissipates and any
residual is left in small overall rotation of the star.
C) The
rotation rate increases and results in fast rotation of the star.
D) The rotation rate increases and results in a disk of material
around a protostar.
E) The rotation increases the speed of
collapse and produces more massive stars.
Answer: D
21) Which of the following may be caused by a protostellar disk?
A) protostellar jets
B) protostellar winds
C)
accretion of material onto the star
D) relatively slow
protostellar rotation
E) all of the above
Answer: E
22) When does a protostar become a true star?
A) when the star
is 1 million years old
B) when the central temperature reaches 1
million Kelvin
C) when nuclear fusion begins in the core
D) when the thermal energy becomes trapped in the center
E) when the stellar winds and jets blow away the surrounding material
Answer: C
23) How long does the protostellar stage last for a star like our
Sun?
A) 1 million years
B) 3 million years
C) 10
million years
D) 30 million years
E) 100 million years
Answer: D
24) What is the range of timescales for star formation?
A) from
1 million years for the most massive stars up to 10 million years for
the least massive stars
B) from 1 million years for the most
massive stars up to 100 million years for the least massive stars
C) from 1 million years for the least massive stars up to 10
million years for the most massive stars
D) from 1 million years
for the least massive stars up to 100 million years for the most
massive stars
E) about 30 million years for all stars, whatever mass
Answer: B
25) What species absorbs photons in a protostar's outer layers?
A) H
B) H2
C) H+
D) H-
E) dust
Answer: D
26) When does a star become a main-sequence star?
A) when the
protostar assembles from a molecular cloud
B) the instant when
hydrogen fusion first begins in the star's core
C) when the rate
of hydrogen fusion within the star's core is high enough to maintain
gravitational equilibrium
D) when a star becomes luminous enough
to emit thermal radiation
E) when hydrogen fusion is occurring
throughout a star's interior
Answer: C
27) 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 and luminosity decrease.
D) Its surface
temperature decreases and its luminosity increases.
E) Its
surface temperature and luminosity remain the same.
Answer: A
28) What happens to the surface temperature and luminosity when a
protostar undergoes convective contraction?
A) Its surface
temperature and luminosity increase.
B) Its surface temperature
remains the same and its luminosity decreases.
C) Its surface
temperature and luminosity decrease.
D) Its surface temperature
decreases and its luminosity increases.
E) Its surface
temperature and luminosity remain the same.
Answer: B
29) What happens to the surface temperature and luminosity when a
protostar radiatively contracts?
A) Its surface temperature and
luminosity increase.
B) Its surface temperature remains the same
and its luminosity decreases.
C) Its surface temperature and
luminosity decrease.
D) Its surface temperature decreases and
its luminosity increases.
E) Its surface temperature and
luminosity remain the same.
Answer: A
30) When does hydrogen first begin to fuse into helium in the star
formation process?
A) when the cloud first begins to contract
B) when the thermal pressure is trapped at the center of the
cloud
C) when the protostars undergoes convective contraction
D) when the protostar undergoes radiative contraction
E)
only when the star reaches the main-sequence
Answer: D
31) About how many times more luminous than our Sun is a young solar
mass protostar just beginning convective contraction?
A) 2-5
B) 5-10
C) 10-100
D) 100-1000
E) a million
Answer: C
32) What is the smallest mass a newborn star can have?
A) 8
times the mass of Jupiter
B) 80 times the mass of Jupiter
C) 800 times the mass of Jupiter
D) about 1/80 the mass of
our Sun
E) about 1/800 the mass of our Sun
Answer: B
33) What are the letters that follow the spectral sequence OBAFGKM?
A) NP
B) YZ
C) LT
D) CD
E) UV
Answer: C
34) What is the greatest mass a newborn star can have
A) 10
solar masses.
B) 20 solar masses.
C) 50 solar masses.
D) 150 solar masses.
E) 300 solar masses.
Answer: D
35) No stars have been found with masses greater than 300 times our
Sun because
A) molecular clouds do not have enough material to
form such massive stars.
B) they would fragment into binary
stars because of their rapid rotation.
C) they would generate so
much power that they would blow themselves apart.
D) they shine
exclusively at X-ray wavelengths and become difficult to detect.
E) they are not bright enough to be seen nearby.
Answer: C
36) For every star with a mass greater than 10 solar masses, about
how many stars are there with masses less than a solar mass?
A)
1
B) 3
C) 10
D) 30
E) 200
Answer: E
37) Which of the following discoveries, if they existed, would
necessitate a reevaluation of our ideas of stellar formation?
A)
a cluster of stars that appeared to be 13 billion years old
B) a
100-solar-mass star
C) a 0.01-solar-mass star
D) a
molecular cloud without any stars
E) planetary systems around
other stars than our own
Answer: C
38) What prevents a brown dwarf from undergoing nuclear fusion?
A) Degeneracy pressure halts the contraction of a protostar so
the core never becomes hot or dense enough for nuclear fusion.
B) There is not enough mass to maintain nuclear reactions in a
self-sustaining way.
C) The surface temperature never rises high
enough for the radiation to be trapped and heat their interior to the
temperatures required for nuclear fusion.
D) Radiation pressure
halts the contraction of a protostar so the core never becomes hot or
dense enough for nuclear fusion.
E) There are too many heavy
elements and not enough hydrogen for fusion to occur in a
self-sustaining way.
Answer: A
39) What is the eventual fate of a brown dwarf?
A) It remains
the same forever.
B) It gradually cools down and becomes ever
dimmer.
C) It gradually contracts and heats up until nuclear
fusion ignites in its interior and it becomes a faint star.
D)
It becomes ever denser and hotter until it becomes a white dwarf.
E) Gravity ultimately "wins" and it becomes a small
black hole.
Answer: B
40) Where would a brown dwarf be located on an H-R diagram?
A)
upper right
B) on the lower part of the main sequence
C)
below and to the right of the lowest part of the main sequence
D) lower left
E) above and to the left of the main sequence
Answer: C
1) The most common constituent of molecular clouds, H2, is rarely detected within them.
Answer: TRUE
2) Molecular clouds appear more transparent at longer wavelengths.
Answer: TRUE
3) Clouds that appear dark in visible light often glow when observed at long infrared wavelengths.
Answer: TRUE
4) Most stars are born in clusters containing thousands of stars.
Answer: TRUE
5) Stars only form in molecular clouds that contain more than 100 times the mass of our Sun.
Answer: FALSE
6) No stars have been found composed solely of Hydrogen and Helium (and no heavier elements).
Answer: TRUE
7) Photographs of many young stars show long jets of material apparently being ejected from their poles.
Answer: TRUE
9) Protostars start off more luminous than the main sequence stars they become.
Answer: TRUE
10) In any star cluster, stars with lower masses greatly outnumber those with higher masses.
Answer: TRUE
1) What do we mean by the interstellar medium?
A) The gas and
dust that lies in between the stars in the Milky Way Galaxy.
B)
The dust that fills the halo of the Milky Way Galaxy.
C) The
middle section of the Milky Way Galaxy.
D) The name of an oracle
who can channel messages from beings that live near the star called Vega.
Answer: A
2) The interstellar clouds called molecular clouds are
A) the
clouds in which elements such as carbon, nitrogen, and oxygen are
made.
B) clouds that are made mostly of complex molecules such as
carbon dioxide and sulfur dioxide.
C) the hot clouds of gas
expelled by dying stars.
D) the cool clouds in which stars form.
Answer: D
3) Which of the following types of molecule is the most abundant in
an interstellar molecular cloud?
A) CO
B) H2O
C) H2
D) NH3
Answer: C
4) Interstellar dust consists mostly of
A) ozone
"smog."
B) microscopic particles of carbon and
silicon.
C) hydrogen and helium atoms.
D) tiny grains of
water ice.
E) the same tiny particles found in household dust.
Answer: B
5) Which part of the electromagnetic spectrum generally gives us our
best views of stars forming in dusty clouds?
A) visible light
B) ultraviolet
C) infrared
D) blue light
Answer: C
6) Suppose you look by eye at a star near the edge of a dusty
interstellar cloud. The star will look ________ than it would if it
were outside the cloud.
A) dimmer and bluer
B) more
redshifted
C) brighter and redder
D) dimmer and redder
Answer: D
7) Most interstellar clouds remain stable in size because the force
of gravity is opposed by ________ within the cloud.
A)
degeneracy pressure
B) radiation pressure
C) stellar winds
D) thermal pressure
Answer: D
8) What kind of gas cloud is most likely to give birth to stars?
A) a hot, dense gas cloud
B) a cold, dense gas cloud
C) a cold, low-density gas cloud
D) a hot, low-density gas cloud
Answer: B
9) What effect are magnetic fields thought to have on star formation
in molecular clouds?
A) They can help resist gravity, so that
more total mass is needed before the cloud can collapse to form stars.
B) They accelerate the star formation process.
C) They
allow small stars to form in isolation within gas clouds.
D)
None—there are no magnetic fields in interstellar space.
Answer: A
10) Which of the following statements is probably true about the very
first stars in the universe?
A) They were made only from
hydrogen and helium.
B) They were made from pure energy.
C) They were probably orbited only by terrestrial planets, but
no jovian planets.
D) They were made approximately of 98%
hydrogen and helium, and 2% of heavier elements.
Answer: A
11) What is a protostar?
A) a star that has planets
B) an
intermediate-mass star
C) a star that is still in the process of
forming
D) a star in its final stage of life
Answer: C
12) Which of the following phenomena is not commonly associated with
the star formation process?
A) the formation of a spinning disk
of material around a protostar
B) powerful "jets"
shooting out along the rotation axis of a protostar
C) strong
winds of particles blowing out into space from a protostar
D)
intense ultraviolet radiation coming from a protostar
Answer: D
13) What law explains why a collapsing cloud usually forms a
protostellar disk around a protostar?
A) Kepler's third law
B) the universal law of gravitation
C) Wien's law
D)
conservation of angular momentum
Answer: D
14) What can we learn about a star from a life track on an H-R
diagram?
A) the star's age
B) the surface temperature and
luminosity the star will have at each stage of its life
C) the
star's current stage of life
D) how the star's distance from
Earth varies at different times in its life
Answer: B
15) When does a protostar become a main-sequence star?
A) when
the rate of hydrogen fusion becomes high enough to balance the rate at
which the star radiates energy into space
B) when a piece of a
molecular cloud first begins to contract into a star
C) when it
becomes luminous enough to emit thermal radiation
D) at the
instant that the first hydrogen fusion reactions occur in the
protostar's core
Answer: A
16) Approximately what core temperature is required before hydrogen
fusion can begin in a star?
A) 10,000 K
B) 10 million K
C) 1 billion K
D) 10 billion K
E) 10 trillion K
Answer: B
17) Which star spends the longest time in the protostellar phase of
life?
A) a 1-solar-mass star
B) a 2-solar-mass star
C) a 3-solar-mass star
D) a 4-solar-mass star
E) a
5-solar-mass star
Answer: A
18) What is the approximate range of masses that newborn
main-sequence stars can have?
A) 0.001 to 150 solar masses
B) 0.1 to 1,000 solar masses
C) 0.1 to 150 solar masses
D) 0.001 to 10 solar masses
E) 0.1 to 10 solar masses
Answer: C
19) The vast majority of stars in a newly formed star cluster
are
A) very high-mass, type O and B stars.
B) red
giants.
C) about the same mass as our Sun.
D) less massive
than the Sun.
Answer: D
20) Which of the following statements about brown dwarfs is not true?
A) Brown dwarfs eventually collapse to become white dwarfs.
B) Brown dwarfs are supported against gravity by degeneracy
pressure, which does not depend on the object's temperature.
C)
Brown dwarfs form like ordinary stars but are too small to sustain
nuclear fusion in their cores.
D) All brown dwarfs have masses
less than about 8% that of our Sun.
Answer: A
1) Which two processes can generate energy to help a star or gas
cloud maintain its internal thermal pressure?
A) nuclear fusion
and nuclear fission
B) nuclear fusion and supernovae
C)
nuclear fission and supernovae
D) nuclear fusion and
gravitational contraction
Answer: D
3) How do we learn the chemical composition of the interstellar
medium?
A) We make an educated guess based on the Sun's
composition.
B) By studying spectra of interstellar gas clouds.
C) We collect samples of gas and dust from interstellar space.
D) We use computer simulations of the interstellar medium.
Answer: B
4) What happens to the visible light radiated by stars located within
a dusty gas cloud?
A) It is blocked by dust and its energy is
thereby lost.
B) It is absorbed by dust, which heats the dust
grains so that they emit the absorbed energy as infrared light.
C) It is reflected by dust back to the star from whence it came.
D) It passes through the cloud unaffected.
Answer: B
5) Under which circumstances can you be sure that the thermal
pressure within a gas cloud is increasing?
A) The cloud's
temperature and density are both increasing.
B) The cloud's
temperature is increasing and its density is decreasing.
C) The
cloud's temperature and density are both decreasing.
D) The
cloud's temperature is decreasing and its density is increasing.
E) It is impossible to say.
Answer: A
6) Which process is required to allow a gravitationally-collapsing
gas cloud to continue to collapse?
A) The cloud must trap most
of its thermal energy.
B) The cloud must collide with other
clouds.
C) New dust particles must continually be made in the
cloud.
D) The cloud must radiate away much of its thermal energy.
Answer: D
7) According to current understanding, how did the first generation
of stars differ from stars born today?
A) They contained much
more hydrogen and helium than stars born today.
B) They were
much cooler in temperature than most stars born today.
C) They
were much more likely to be members of binary star systems than stars
are born today.
D) They were much more massive than most stars
born today.
Answer: D
8) Angular momentum plays an important role in star formation. Which
of the following characteristics of a protostellar system is probably
not strongly affected by the star's angular momentum?
A) the
existence of protostellar jets
B) the strength of protostellar
winds
C) the onset of core hydrogen fusion
D) the formation of a protostellar disk
Answer: C
9) Close binary star systems are thought to form when
A) two
interstellar gas clouds happen to contract so close together that
there's no room for a disk or planets.
B) the protostellar disk
around a protostar has enough material to form a second star.
C)
gravity pulls two neighboring protostars quite close together, but
angular momentum causes them to orbit each other rather than
colliding.
D) a protostar emits two jets, each of which turns
into a star.
Answer: C
10) Generally speaking, how does the surface temperature and
luminosity of a protostar compare to the surface temperature and
luminosity of the main-sequence star it becomes?
A) A
main-sequence star is hotter and brighter than it was as a protostar.
B) A main-sequence star is cooler and dimmer than it was as a
protostar.
C) A main-sequence star is cooler and brighter than
it was as a protostar.
D) A main-sequence star is hotter and
dimmer than it was as a protostar.
Answer: D
11) Where does a 1-solar-mass protostar appear on an H-R diagram?
A) to the right of the main sequence, and lower down than the
Sun
B) to the right of the main sequence, and higher up than the
Sun
C) to the left of the main sequence, and higher up than the
Sun
D) Nowhere—only stars that have fusion in their cores can be
shown on H-R diagrams.
Answer: B
12) Why does the rotation of a protostar slow down over time?
A) All rotating objects slow down over time.
B) Magnetic
fields can transfer angular momentum to the protostellar disk and
protostellar winds can carry angular momentum away.
C) The onset
of fusion causes the rotation rate to slow dramatically.
D)
Magnetic fields of other stars interact with the magnetic fields of
the protostars, slowing its rotation.
Answer: B
13) The surface of a protostar radiates energy while its core
A)
shrinks and cools.
B) shrinks and maintains a constant
temperature.
C) shrinks and heats.
D) expands and cools.
Answer: C
14) The core of a protostar that will eventually become a brown dwarf
shrinks until
A) the type of pressure called degeneracy pressure
becomes important.
B) its central temperature is high enough to
support fusion reactions.
C) it forms a rocky core.
D) it
radiates brown light.
Answer: A
15) If a star is extremely massive (well over 100 solar masses), why
isn't it likely to survive for long?
A) It explodes as a
supernova after just a few dozen years.
B) It may blow itself
apart because of radiation pressure.
C) It eventually divides
into two lower-mass stars.
D) Its great mass will cause it to
suck itself into becoming a black hole.
Answer: B
16) Consider a large molecular cloud that will give birth to a
cluster of stars. Which of the following would you expect to be true?
A) All the stars in the cluster will be of about the same mass.
B) A few massive stars will form, live, and die before the
majority of the star's clusters even complete their protostar stage.
C) All the stars in the cluster will become main-sequence stars
at about the same time.
D) All the stars in the cluster will
have approximately the same luminosity and surface temperature.
Answer: B
17) We do not know for certain whether the general trends we observe
in stellar birth masses also apply to brown dwarfs. But if they do,
then which of the following would be true?
A) Brown dwarfs would
outnumber all ordinary stars.
B) Brown dwarfs would be
responsible for most of the overall luminosity of our Milky Way
Galaxy.
C) Brown dwarfs would be extremely rare.
D) Most
of the brown dwarfs in the Milky Way Galaxy would be quite young in age.
Answer: A
18) Where would a brown dwarf be located on an H-R diagram?
A)
above and to the left of the highest part of the main sequence
B) in the upper right corner of the H-R diagram
C) in the
lower left corner of the H-R diagram
D) below and to the right
of the lowest part of the main sequence
Answer: D
1) What do astronomers mean when they say that we are all "star
stuff"?
A) that life would be impossible without energy
from the Sun
B) that Earth formed at the same time as the Sun
C) that the carbon, oxygen, and many elements essential to life
were created by nucleosynthesis in stellar cores
D) that the Sun
formed from the interstellar medium: the "stuff" between the
stars
E) that the Universe contains billions of stars
Answer: C
3) What type of star is our Sun?
A) low-mass star
B)
intermediate-mass star
C) high-mass star
Answer: A
4) What is the range of star masses for high-mass stars?
A)
between 500 and about 1,000 solar masses
B) between 200 and
about 500 solar masses
C) between 8 and about 100 solar masses
D) between 2 and about 10 solar masses
E) between 2 and
about 5 solar masses
Answer: C
5) What can we learn about a star from a life track on an H-R
diagram?
A) how long ago it was born
B) when it will die
C) where it is located
D) what surface temperature and
luminosity it will have at each stage of its life
E) all of the above
Answer: D
6) Which of the following statements about degeneracy pressure is not
true?
A) Degeneracy pressure varies with the temperature of the
star.
B) Degeneracy pressure can halt gravitational contraction
of a star even when no fusion is occurring in the core.
C)
Degeneracy pressure keeps any protostar less than 0.08 solar mass from
becoming a true, hydrogen-fusing star.
D) Degeneracy pressure
arises out of the ideas of quantum mechanics.
E) Degeneracy
pressure supports white dwarfs against gravity.
Answer: A
7) All of the following are involved in carrying energy outward from
a star's core except
A) convection.
B) radiative
diffusion.
C) conduction.
D) neutrinos.
Answer: C
8) Which stars have convective cores?
A) low-mass stars
B) intermediate-mass stars
C) high-mass stars
D) all
of the above
E) none of the above
Answer: C
9) Which of the following spectral types is more likely to be a flare
star?
A) KIII
B) MV
C) GV
D) I
E) BII
Answer: B
10) 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
Answer: E
11) What happens when a star exhausts its core hydrogen supply?
A) Its core contracts, but its outer layers expand and the star
becomes bigger and brighter.
B) It contracts, becoming smaller
and dimmer.
C) It contracts, becoming hotter and brighter.
D) It expands, becoming bigger but dimmer.
E) Its core
contracts, but its outer layers expand and the star becomes bigger but
cooler and therefore remains at the same brightness.
Answer: A
12) What is happening inside a star while it expands into a subgiant?
A) It is fusing hydrogen into helium in the core.
B) It is
fusing hydrogen into helium in a shell outside the core.
C) It
is fusing helium into carbon in the core.
D) It is fusing helium
into carbon in a shell outside the core.
E) It is not fusing any
element; it is contracting and heating up.
Answer: B
13) Compared to the star it evolved from, a red giant is
A)
hotter and brighter.
B) hotter and dimmer.
C) cooler and
brighter.
D) cooler and dimmer.
E) the same temperature
and brightness.
Answer: C
14) At approximately what temperature can helium fusion occur?
A) 100,000 K
B) 1 million K
C) a few million K
D) 100 million K
E) 100 billion K
Answer: D
15) Why does a star grow larger after it exhausts its core hydrogen?
A) The outer layers of the star are no longer gravitationally
attracted to the core.
B) Hydrogen fusion in a shell outside the
core generates enough thermal pressure to push the upper layers
outward.
C) Helium fusion in the core generates enough thermal
pressure to push the upper layers outward.
D) Helium fusion in a
shell outside the core generates enough thermal pressure to push the
upper layers outward.
E) The internal radiation generated by the
hydrogen fusion in the core has heated the outer layers enough that
they can expand after the star is no longer fusing hydrogen.
Answer: B
16) How many helium nuclei fuse together when making carbon?
A)
2
B) 3
C) 4
D) varies depending on the reaction
E) none of the above
Answer: B
17) The helium fusion process results in the production of
A)
hydrogen.
B) oxygen.
C) carbon.
D) nitrogen.
E) iron.
Answer: C
18) What happens after a helium flash?
A) The core quickly
heats up and expands.
B) The star breaks apart in a violent
explosion.
C) The core suddenly contracts.
D) The core
stops fusing helium.
E) The star starts to fuse helium in a
shell outside the core.
Answer: A
19) What is a carbon star?
A) a red giant star whose atmosphere
becomes carbon-rich through convection from the core
B) a star
that fuses carbon in its core
C) another name for a white dwarf,
a remnant of a star made mainly of carbon
D) a star that
produces carbon by fusion in its atmosphere
E) a star that is
made at least 50 percent of carbon
Answer: A
20) What is a planetary nebula?
A) a disk of gas surrounding a
protostar that may form into planets
B) what is left of the
planets around a star after a low-mass star has ended its life
C) the expanding shell of gas that is no longer gravitationally
held to the remnant of a low-mass star
D) the molecular cloud
from which protostars form
E) the expanding shell of gas that is
left when a white dwarf explodes as a supernova
Answer: C
21) What happens to the core of a star after a planetary nebula
occurs?
A) It contracts from a protostar to a main-sequence
star.
B) It breaks apart in a violent explosion.
C) It
becomes a white dwarf.
D) It becomes a neutron star.
E)
none of the above
Answer: C
22) Which of the following sequences correctly describes the stages
of life for a low-mass star?
A) red giant, protostar,
main-sequence, white dwarf
B) white dwarf, main-sequence, red
giant, protostar
C) protostar, red giant, main-sequence, white
dwarf
D) protostar, main-sequence, white dwarf, red giant
E) protostar, main-sequence, red giant, white dwarf
Answer: E
23) Compared to the star it evolved from, a white dwarf is
A)
hotter and brighter.
B) hotter and dimmer.
C) cooler and
brighter.
D) cooler and dimmer.
E) the same temperature
and brightness.
Answer: B
24) Most interstellar dust grains are produced in
A) the Big
Bang.
B) the interstellar medium.
C) the atmospheres of
red giant stars.
D) supernova explosions.
E) the solar nebula.
Answer: C
25) During which stage is the star's energy supplied by gravitational
contraction?
A) ii
B) iii
C) v
D) vi
E) viii
Answer: A
26) During which stage does the star have an inert (nonburning)
helium core?
A) iii
B) iv
C) vi
D) vii
E) viii
Answer: B
27) During which stage does the star have an inert (nonburning)
carbon core?
A) ii
B) iii
C) iv
D) vi
E) viii
Answer: E
28) Which stage lasts the longest?
A) i
B) iii
C)
iv
D) vi
E) viii
Answer: B
29) What will happen to the star after stage viii?
A) It will
explode in a supernova.
B) It will begin burning carbon in its
core.
C) It will eject a planetary nebula.
D) It will
collapse to make a neutron star.
E) It will gain mass until it
collapses under its own weight.
Answer: C
30) In the end, the remaining core of this star will be left behind
as
A) a white dwarf made primarily of carbon and oxygen.
B) a white dwarf made primarily of silicon and iron.
C) a
neutron star.
D) a black hole.
E) a supernova.
Answer: A
31) Based on its main-sequence turnoff point, the age of this cluster
is
A) less than 1 billion years.
B) about 1 billion years.
C) about 2 billion years.
D) about 10 billion years.
E) more than 15 billion years.
Answer: D
32) Which statement about this cluster is not true?
A) It is
likely to be located in the halo of the galaxy.
B) It contains
some stars that are burning helium in their cores.
C) It is the
type of cluster known as an open cluster of stars.
D) It
probably contains no young stars at all.
E) It is likely to be
spherical in shape.
Answer: C
33) Consider the star to which the arrow points. How is it currently
generating energy?
A) by gravitational contraction
B) by
hydrogen shell burning around an inert helium core
C) by core
hydrogen fusion
D) by core helium fusion combined with hydrogen
shell burning
E) by both hydrogen and helium shell burning
around an inert carbon core
Answer: B
34) Consider the star to which the arrow points. Which of the
following statements about this star is not true?
A) It is
significantly less massive than the Sun.
B) It is larger in
radius than the Sun.
C) It is brighter than the Sun.
D)
Its surface temperature is lower than the Sun's.
E) Its core
temperature is higher than the Sun's.
Answer: A
35) What is the CNO cycle?
A) the process by which helium is
fused into carbon, nitrogen, and oxygen
B) the process by which
carbon is fused into nitrogen and oxygen
C) a type of hydrogen
fusion that uses carbon, nitrogen, and oxygen atoms as catalysts
D) the period of a massive star's life when carbon, nitrogen,
and oxygen are fusing in different shells outside the core
E)
the period of a low-mass star's life when it can no longer fuse
carbon, nitrogen, and oxygen in its core
Answer: C
37) What happens when the gravity of a massive star is able to
overcome neutron degeneracy pressure?
A) The core contracts and
becomes a white dwarf.
B) The core contracts and becomes a ball
of neutrons.
C) The core contracts and becomes a black hole.
D) The star explodes violently, leaving nothing behind.
E)
Gravity is not able to overcome neutron degeneracy pressure.
Answer: C
38) What types of stars end their lives with supernovae?
A) all
stars that are red in color
B) all stars that are yellow in
color
C) stars that are at least several times the mass of the
Sun
D) stars that are similar in mass to the Sun
E) stars
that have reached an age of 10 billion years
Answer: C
39) Which of the following statements about stages of nuclear burning
(i.e., first-stage hydrogen burning, second-stage helium burning,
etc.) in a massive star is not true?
A) Each successive stage of
fusion requires higher temperatures than the previous stages.
B)
As each stage ends, the core shrinks further.
C) Each successive
stage creates an element with a higher atomic weight.
D) Each
successive stage lasts for approximately the same amount of time.
Answer: D
40) Suppose the star Betelgeuse (the upper left shoulder of Orion)
were to become a supernova tomorrow (as seen here on Earth). What
would it look like to the naked eye?
A) Because the supernova
event destroys the star, Betelgeuse would suddenly disappear from
view.
B) We'd see a cloud of gas expanding away from the
position where 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.
Answer: C
43) Why is Supernova 1987A particularly important to astronomers?
A) It occurred only a few dozen light-years from Earth.
B)
It provided the first evidence that supernovae really occur.
C)
It provided the first evidence that neutron stars really exist.
D) It was the first supernova detected in nearly 400 years.
E) It was the nearest supernova detected in nearly 400 years.
Answer: E
45) You discover a binary star system in which one member is a15MSun
main-sequence star and the other star is a 10MSun giant. How do we
believe that a star system such as this might have come to exist?
A) The giant must once have been the more massive star but
transferred some of its mass to its companion.
B) Despite the
low odds of finding a system with two such massive stars, there is
nothing surprising about the fact that such systems exist.
C)
The two stars probably were once separate but became a binary when a
close encounter allowed their mutual gravity to pull them together.
D) The main-sequence star probably is a pulsating variable star
and therefore appears to be less massive than it really is.
E)
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 star millions of years later than its less massive companion.
Answer: A
46) Why do scientists think that our solar system must have formed
sometime after nearby supernovae explosions?
A) Existence of
heavy elements
B) Solar temperature too low
C) Our Sun is
a G-type star
D) They don't—scientists believe our Sun is among
the first generation of stars.
Answer: A
1) Photographs of many young stars show long jets of material apparently being ejected from their poles.
Answer: TRUE
2) Although some photographs show what looks like jets of material near many young stars, we now know that these "jets" actually represent gas from the surrounding nebula that is falling onto the stars.
Answer: FALSE
3) In any star cluster, stars with lower masses greatly outnumber those with higher masses.
Answer: TRUE
5) Stars with high masses live longer than stars with lower masses.
Answer: FALSE
4) There is no limit to the mass with which a star can be born.
Answer: FALSE
6) Stars of lower mass have deeper convection zones outside their cores than stars of higher mass.
Answer: TRUE
7) Convection never occurs in the core of any type of star.
Answer: FALSE
8) The helium fusion process works by fusing two helium nuclei into one beryllium nucleus.
Answer: FALSE
) Our Sun will end its life in a planetary nebula and become a white dwarf.
Answer: TRUE
10) The most massive stars generate energy at the end of their lives by fusing iron in their cores.
Answer: FALSE
11) The heaviest element produced by stars or in supernovae is silicon.
Answer: FALSE
12) All stars that become supernovae will leave behind a neutron star.
Answer: FALSE
A. H fusion by the proton-proton chain
B. H fusion by the CNO cycle
C. helium fusion
D. matter-antimatter
annihilation
E. gravitational contraction
1) Which method of energy generation is used by the Sun today?
Answer: A
A. H fusion by the proton-proton chain
B. H fusion by the CNO
cycle
C. helium fusion
D. matter-antimatter
annihilation
E. gravitational contraction
2) Which one provided the energy that made the Sun hot in the first place?
Answer: E
A. H fusion by the proton-proton chain
B. H fusion by the CNO
cycle
C. helium fusion
D. matter-antimatter
annihilation
E. gravitational contraction
3) Which method of energy generation provides the source of energy for a protostar?
Answer: E
A. H fusion by the proton-proton chain
B. H fusion by the CNO
cycle
C. helium fusion
D. matter-antimatter
annihilation
E. gravitational contraction
4) Which process leads to the production of carbon?
Answer: C
A. H fusion by the proton-proton chain
B. H fusion by the CNO
cycle
C. helium fusion
D. matter-antimatter
annihilation
E. gravitational contraction
5) When a 1-solar-mass star stabilizes as a giant for about a billion years, which method of energy generation occurs in its central core?
Answer: C
A. H fusion by the proton-proton chain
B. H fusion by the CNO
cycle
C. helium fusion
D. matter-antimatter
annihilation
E. gravitational contraction
6) Which one is used by a main-sequence star of spectral type B2?
Answer: B
A. H fusion by the proton-proton chain
B. H fusion by the CNO
cycle
C. helium fusion
D. matter-antimatter
annihilation
E. gravitational contraction
7) Which method of energy generation provides the source of energy for a 10MSun main-sequence star?
Answer: B
1) Which of the following stars will live longest?
A) a
1-solar-mass star
B) a 2-solar-mass star
C) a 3-solar-mass
star
D) a 4-solar-mass star
E) a 5-solar-mass star
Answer: A
2) In the context of understanding stellar lives,
"high-mass" stars have masses
A) more than about 8
times the mass of our Sun.
B) more than about 3 times the mass of
our Sun.
C) more than twice the mass of our Sun.
D) more
than 20 times the mass of our Sun.
Answer: A
3) Which of the following lists the stages of life for a low-mass
star in the correct order?
A) protostar, main-sequence star, red
giant, planetary nebula, white dwarf
B) protostar, main-sequence
star, red giant, supernova, neutron star
C) protostar,
main-sequence star, planetary nebula, red giant
D) main-sequence
star, white dwarf, red giant, planetary nebula, protostar
Answer: A
4) What happens when a main-sequence star exhausts its core hydrogen
fuel supply?
A) The entire star shrinks in size.
B) The
core shrinks while the rest of the star expands.
C) The core
immediately begins to fuse its helium into carbon.
D) The star
becomes a neutron star.
Answer: B
5) The main source of energy for a star as it grows in size to become
a red giant is
A) hydrogen fusion in the central core.
B)
helium fusion in the central core.
C) hydrogen fusion in a shell
surrounding the central core.
D) gravitational contraction.
Answer: C
6) The overall helium fusion reaction is
A) three helium nuclei
fuse to form one carbon nucleus.
B) two helium nuclei fuse to
form one beryllium nucleus.
C) two hydrogen nuclei fuse to form
one helium nucleus.
D) four helium nuclei fuse to form one
oxygen nucleus.
Answer: A
7) What is a helium flash?
A) The ignition of helium shell
burning in a high-mass star with a carbon core.
B) A sudden
brightening of a low-mass star, detectable from Earth by observing
spectral lines of helium.
C) It is another name for the helium
fusion reaction.
D) The sudden onset of helium fusion in the
core of a low-mass star.
Answer: D
8) An H-R diagram for a globular cluster will show a horizontal
branch—a line of stars above the main-sequence but to the left of the
subgiants and red giants.
Which of the following statements about
these horizontal branch stars is true?
A) They have inert
(non-burning) carbon cores.
B) Their sole source of energy is
hydrogen shell burning.
C) They generate energy through both
hydrogen fusion and helium fusion.
D) In a particular star
cluster, all horizontal branch stars have the same spectral type.
Answer: C
9) What is a planetary nebula?
A) gas created from the remains
of planets that once orbited a dead star
B) interstellar gas
from which planets are likely to form in the not-too-distant future
C) the remains of a high-mass star that has exploded
D)
gas ejected from a low-mass star in the final stage of its life
Answer: D
10) The ultimate fate of our Sun is to
A) explode in a
supernova.
B) become a white dwarf that will slowly cool with
time.
C) become a rapidly spinning neutron star.
D) become a
black hole.
Answer: B
11) Which low-mass star does not have fusion occurring in its central
core?
A) a main-sequence star
B) a red giant
C) a
helium-burning star
Answer: B
12) How are low-mass red giant stars important to our existence?
A) These stars manufactured virtually all the elements out of
which we and our planet are made.
B) These stars generate the
energy that makes life on Earth possible.
C) These stars
manufactured most of the carbon atoms in our bodies.
D) These
stars provide most of the light that reaches us from globular clusters.
Answer: C
13) Which of the following pairs of atomic nuclei would feel the
strongest repulsive electromagnetic force if you tried to push them
together?
A) helium and helium
B) hydrogen and hydrogen
C) hydrogen and helium
D) hydrogen and deuterium
Answer: A
14) Which of the following stars will certainly end its life in a
supernova?
A) the Sun
B) a red giant star
C) a
10-solar-mass star
D) a neutron star
Answer: C
15) What is the CNO cycle?
A) a set of steps by which four
hydrogen nuclei fuse into one helium nucleus
B) the process by
which helium is fused into carbon, nitrogen, and oxygen
C) the
process by which carbon is fused into nitrogen and oxygen
D) the
set of fusion reactions that have produced all the carbon, nitrogen,
and oxygen in the universe
Answer: A
16) In order to predict whether a star will eventually fuse oxygen
into a heavier element, what do you need to know about the star?
A) its luminosity
B) its overall abundance of elements
heavier than helium
C) how much oxygen it now has in its core
D) its mass
Answer: D
17) Why is iron significant to understanding how a supernova occurs?
A) Iron is the heaviest of all atomic nuclei, and thus no
heavier elements can be made.
B) Supernovae often leave behind
neutron stars, which are made mostly of iron.
C) The fusion of
iron into uranium is the reaction that drives a supernova explosion.
D) Iron cannot release energy either by fission or fusion.
Answer: D
18) After a supernova explosion, the remains of the stellar
core
A) will always be a neutron star.
B) be either a
neutron star or a black hole.
C) will always be a black
hole.
D) may be either a white dwarf, neutron star, or black hole
Answer: B
19) Why is Supernova 1987A particularly important to astronomers?
A) It is the nearest supernova to have occurred at a time when
we were capable of studying it carefully with telescopes.
B) It
was the first supernova detected in nearly 400 years.
C) It
provided the first evidence that supernovae really occur.
D) It
occurred only a few light-years from Earth.
Answer: A
20) Algol consist of a 3.7 MSun main-sequence star and a 0.8 MSun
subgiant. Why does this seem surprising, at least at first?
A)
The two stars in a binary system should both be at the same stage of
life; that is, they should either both be main-sequence stars or both
be subgiants.
B) It doesn't make sense to find a subgiant in a
binary star system.
C) The two stars should be the same age, so
we'd expect the subgiant to be more massive than the main-sequence
star.
D) A star with a mass of 3.7 MSun is too big to be a
main-sequence star.
Answer: C
21) Where does gold (the element) come from?
A) It is produced
by mass transfer in close binaries.
B) It is produced during the
supernova explosions of high-mass stars.
C) It is produced
during the late stages of fusion in low-mass stars.
D) It was
produced during the Big Bang.
Answer: B
1) Sun is considered to be a
A) low-mass star.
B)
intermediate-mass star
C) high-mass star.
D) brown dwarf.
Answer: A
2) Which of the following types of data provide evidence that helps
us understand the life tracks of low-mass stars?
A) H-R diagrams
of open clusters
B) observing a low-mass star over many years
C) H-R diagrams of globular clusters
D) spacecraft
observations of the Sun
Answer: C
3) Why is a 1 solar-mass red giant more luminous than a 1 solar-mass
main-sequence star?
A) The red giant has a hotter core.
B)
The red giant's surface is hotter.
C) The red giant is more
massive.
D) Fusion reactions are producing energy at a greater
rate in the red giant.
Answer: D
4) Which of the following describes a star with a hydrogen-burning
shell and an inert helium core?
A) It is a red giant that grows
in luminosity until it dies in a planetary nebula.
B) It is a
subgiant that gradually grows dimmer as its hydrogen-burning shell
expands and cools.
C) It is a subgiant that grows in luminosity
until helium fusion begins in the central core.
D) It is what is
known as a helium-burning star, which has both helium fusion in its
core and hydrogen fusion in a shell.
Answer: C
5) 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) decades of continuous monitoring of red
giants in a globular cluster
C) observing the structures of
planetary nebulae
D) neutrino detections from nearby supernovae
Answer: B
6) Which is more common: a star blows up as a supernova, or a star
forms a planetary nebula/white dwarf system?
A) Supernovae are
more common.
B) Planetary nebula formation is more common.
C) They both occur in about equal numbers.
D) It is
impossible to say.
Answer: B
12) Carbon fusion occur in high-mass stars but not in low-mass stars
because
A) the cores of low-mass stars never contain significant
amounts of carbon.
B) the cores of low-mass stars never get hot
enough for carbon fusion.
C) only high-mass stars do fusion by
the CNO cycle.
D) carbon fusion can occur only in the stars known
as carbon stars.
Answer: B
14) Which event marks the beginning of a supernova?
A) the
sudden collapse of an iron core into a compact ball of neutrons
B) the onset of helium burning after a helium flash
C) the
beginning of neon burning in an extremely massive star
D) the
sudden initiation of the CNO cycle
Answer: A
16) 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) Stars would be less massive.
C) All
stars would be red giants.
D) Nuclear fusion could not power stars.
Answer: D
17) 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) The
apparent pattern is thought to be a random coincidence.
B)
Elements with atomic mass numbers divisible by 4 tend to be more
stable than elements in between.
C) At the end of a high-mass
star's life, it produces new elements through a series of helium
capture reactions.
D) This pattern in elemental abundances was
apparently determined during the first few minutes after the Big Bang.
Answer: C
18) A spinning neutron star has been observed at the center of
a
A) planetary nebula.
B) supernova remnant.
C) red
supergiant.
D) protostar.
Answer: B
20) Tidal forces are very 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 in a system like the Algol
system are small compared to their physical separation.
B)
Main-sequence stars are too big to be affected by tidal forces.
C) Main-sequence stars are too massive to be affected by tidal
forces.
D) Main-sequence stars are unaffected by tidally-induced
mass transfer.
Answer: A
1) Degeneracy pressure is the source of the pressure that stops the
crush of gravity in all the following except
A) a brown dwarf.
B) a white dwarf.
C) a neutron star.
D) a very
massive main-sequence star.
E) the central core of the Sun after
hydrogen fusion ceases but before helium fusion begins.
Answer: D
2) White dwarfs are so called because
A) they are both very hot
and very small.
B) they are the end-products of small, low-mass
stars.
C) they are the opposite of black holes.
D) it
amplifies the contrast with red giants.
E) they are supported by
electron degeneracy pressure.
Answer: A
3) A teaspoonful of white dwarf material on Earth would weigh
A) the same as a teaspoonful of Earth-like material.
B)
about the same as Mt. Everest.
C) about the same as Earth.
D) a few tons.
E) a few million tons.
Answer: D
4) Which of the following is closest in mass to a white dwarf?
A) the Moon
B) Earth
C) Jupiter
D)
Neptune
E) the Sun
Answer: E
6) What is the ultimate fate of an isolated white dwarf?
A) It
will cool down and become a cold black dwarf.
B) As gravity
overwhelms the electron degeneracy pressure, it will explode as a
nova.
C) As gravity overwhelms the electron degeneracy pressure,
it will explode as a supernova.
D) As gravity overwhelms the
electron degeneracy pressure, it will become a neutron star.
E)
The electron degeneracy pressure will eventually overwhelm gravity and
the white dwarf will slowly evaporate.
Answer: A
8) Which of the following statements about novae is not true?
A) A star system that undergoes a nova may have another nova
sometime in the future.
B) A nova involves fusion taking place
on the surface of a white dwarf.
C) Our Sun will probably
undergo at least one nova when it becomes a white dwarf about 5
billion years from now.
D) When a star system undergoes a nova,
it brightens considerably, but not as much as a star system undergoing
a supernova.
E) The word nova means "new star" and
originally referred to stars that suddenly appeared in the sky, then
disappeared again after a few weeks or months.
Answer: C
9) What kind of pressure supports a white dwarf?
A) neutron
degeneracy pressure
B) electron degeneracy pressure
C)
thermal pressure
D) radiation pressure
E) all of the above
Answer: B
11) How does a 1.2-solar-mass white dwarf compare to a 1.0-solar-mass
white dwarf?
A) It has a larger radius.
B) It has a
smaller radius.
C) It has a higher surface temperature.
D)
It has a lower surface temperature.
E) It is supported by
neutron, rather than electron, degeneracy pressure.
Answer: B
12) Which of the following is closest in size (radius) to a white
dwarf?
A) Earth
B) a small city
C) a football
stadium
D) a basketball
E) the Sun
Answer: A
13) What kind of star is most likely to become a white-dwarf
supernova?
A) an O star
B) a star like our Sun
C) a
binary M star
D) a white dwarf star with a red giant binary
companion
E) a pulsar
Answer: D
14) Observationally, how can we tell the difference between a
white-dwarf supernova and a massive-star supernova?
A) A
massive-star supernova is brighter than a white-dwarf supernova.
B) A massive-star supernova happens only once, while a
white-dwarf supernova can repeat periodically.
C) The spectrum
of a massive-star supernova shows prominent hydrogen lines, while the
spectrum of a white-dwarf supernova does not.
D) The light of a
white-dwarf supernova fades steadily, while the light of a
massive-star supernova brightens for many weeks.
E) We cannot
yet tell the difference between a massive-star supernova and a
white-dwarf supernova.
Answer: C
16) A teaspoonful of neutron star material on Earth would weigh
A) about the same as a teaspoonful of Earth-like material.
B) a few tons.
C) more than Mt. Everest.
D) more
than the Moon.
E) more than Earth.
Answer: C
17) Which of the following is closest in size (radius) to a neutron
star?
A) Earth
B) a city
C) a football stadium
D) a basketball
E) the Sun
Answer: B
18) Which of the following best describes what would happen if a
1.5-solar-mass neutron star, with a diameter of a few kilometers, were
suddenly (for unexplained reasons) to appear in your hometown?
A) The entire mass of Earth would end up as a thin layer, about
1 cm thick, over the surface of the neutron star.
B) It would
rapidly sink to the center of Earth.
C) The combined mass of
Earth and the neutron star would cause the neutron star to collapse
into a black hole.
D) It would crash through Earth, creating a
large crater, and exit Earth on the other side.
E) It would
crash into Earth, throwing vast amounts of dust into the atmosphere
which in turn would cool Earth. Such a scenario is probably what
caused the extinction of the dinosaurs.
Answer: A
19) From an observational standpoint, what is a pulsar?
A) a
star that slowly changes its brightness, getting dimmer and then
brighter with a period of anywhere from a few hours to a few weeks
B) an object that emits flashes of light several times per
second or more, with near perfect regularity
C) an object that
emits random "pulses" of light that sometimes occur only a
fraction of a second apart and other times stop for several days at a
time
D) a star that changes color rapidly, from blue to red and
back again
E) a star that rapidly changes size as it moves off
the main sequence
Answer: B
]20) From a theoretical standpoint, what is a pulsar?
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
Answer: B
21) What causes the radio pulses of a pulsar?
A) The star
vibrates.
B) As the star spins, beams of radio radiation sweep
through space. If one of the beams crosses Earth, we observe a pulse.
C) The star undergoes periodic explosions of nuclear fusion that
generate radio emission.
D) The star's orbiting companion
periodically eclipses the radio waves emitted by the main pulsar.
E) A black hole near the star absorbs energy and re-emits it as
radio waves.
Answer: B
22) How do we know that pulsars are neutron stars?
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
Answer: C
23) What is the ultimate fate of an isolated pulsar?
A) It will
spin ever faster, becoming a millisecond pulsar.
B) As gravity
overwhelms the neutron degeneracy pressure, it will explode as a
supernova.
C) 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.
E)
The neutron degeneracy pressure will eventually overwhelm gravity and
the pulsar will slowly evaporate.
Answer: D
24) What is the basic definition of a black hole?
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
Answer: C
25) How does the gravity of an object affect light?
A) Light
doesn't have mass; therefore, it is not affected by gravity.
B)
Light coming from a compact massive object, such as a neutron star,
will be redshifted.
C) Light coming from a compact massive
object, such as a neutron star, will be blueshifted.
D) Visible
light coming from a compact massive object, such as a neutron star,
will be redshifted, but higher frequencies such as X rays and gamma
rays will not be affected.
E) Less energetic light will not be
able to escape from a compact massive object, such as a neutron star,
but more energetic light will be able to.
Answer: B
26) How does a black hole form from a massive star?
A) During a
supernova, if a star is massive enough for its gravity to overcome
neutron degeneracy of the core, the core will be compressed until it
becomes a black hole.
B) Any star that is more massive than 8
solar masses will undergo a supernova explosion and leave behind a
black-hole remnant.
C) If enough mass is accreted by a
white-dwarf star so that it exceeds the 1.4-solar-mass limit, it will
undergo a supernova explosion and leave behind a black-hole remnant.
D) If enough mass is accreted by a neutron star, it will undergo
a supernova explosion and leave behind a black-hole remnant.
E)
A black hole forms when two massive main-sequence stars collide.
Answer: A
27) Which of the following statements about black holes is not true?
A) 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.
B) 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.
C) A black hole is truly a hole in spacetime,
through which we could leave the observable universe.
D) 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.
E) If you
fell into a black hole, you would experience time to be running
normally as you plunged rapidly across the event horizon.
Answer: D
28) In some cases, a supernova in a binary system may lead to the
eventual formation of an accretion disk around the remains of the star
that exploded. All of the following statements about such accretion
disks are true except
A) X rays are emitted by the hot gas in the
accretion disk.
B) the accretion disk consists of material that
spills off the companion star.
C) the central object about which
the accretion disk swirls may be either a neutron star or a black
hole.
D) several examples of flattened accretion disks being
"fed" by a large companion star can be seen clearly in
photos from the Hubble Space Telescope.
E) the radiation from an
accretion disk may vary rapidly in time.
Answer: D
29) 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) bright X-ray emission
that varies on a time scale of a few hours
B) spectral lines
from the companion star that alternately shift to shorter and longer
wavelengths
C) sudden, intense X-ray bursts
D) visible and
ultraviolet light from the companion star
Answer: C
A) 3 km
B) 30 km
C) 3,000 km
D) 300 million km
E) 3 million km
Answer: D
32) What do we mean by the singularity of a 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.
Answer: C
31) A 10-solar-mass main-sequence star will produce which of the
following remnants?
A) white dwarf
B) neutron star
C) black hole
D) none of the above
Answer: B
33) How do we know what happens at the event horizon of a black hole?
A) Physicists have created miniature black holes in the lab.
B) Astronomers have sent spacecraft through the event horizon of
a nearby black hole.
C) Astronomers have analyzed the light from
matter within the event horizon of many black holes.
D)
Astronomers have detected X rays from accretion disks around black
holes.
E) We don't know for sure: we only know what to expect
based on the predictions of general relativity.
Answer: E
34) Prior to the 1990s, most astronomers assumed that gamma-ray
bursts came from neutron stars with accretion disks. How do we now
know that this hypothesis was wrong?
A) We now know that
gamma-ray bursts come not from neutron stars but from black holes.
B) Theoretical work has proven that gamma rays cannot be
produced in accretion disks.
C) Observations from the Compton
Gamma-Ray Observatory show that gamma-ray bursts come randomly from
all directions in the sky.
D) Observations from the Compton
Gamma-Ray Observatory show that gamma-ray bursts occur too frequently
to be attributed to neutron stars.
E) Observations from the
Compton Gamma-Ray Observatory have allowed us to trace gamma-ray
bursts to pulsating variable stars in distant galaxies.
Answer: C
35) Why do astronomers consider gamma-ray bursts to be one of the
greatest mysteries in astronomy?
A) because they are so rare
B) because we know they come from pulsating variable stars but
don't know how they are created
C) because the current evidence
suggests that they are the most powerful bursts of energy that ever
occur anywhere in the universe, but we don't know how they are
produced
D) because current evidence suggests that they come
from our own Milky Way, but we have no idea where in the Milky Way
they occur
E) because current evidence suggests that they come
from massive black holes in the centers of distant galaxies, adding to
the mystery of black holes themselves
Answer: C
39) If you were to come back to our Solar System in 6 billion years,
what might you expect to find?
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.
Answer: B
40) Black holes, by definition, cannot be observed directly. What
observational evidence do scientists have of their existence?
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.
Answer: B
1) Brown dwarfs, white dwarfs, and neutrons stars are all kept from collapsing by degeneracy pressure.
Answer: TRUE
2) The upper limit to the mass of a white dwarf is 1.4 solar masses.
Answer: TRUE
3) More massive white dwarfs are smaller than less massive white dwarfs.
Answer: TRUE
4) There is no upper limit to the mass of a neutron star.
Answer: FALSE
The remnant left behind from a white-dwarf supernova is a neutron star.
Answer: FALSE
Our Sun will likely undergo a nova event in about 5 billion years.
Answer: FALSE
All pulsars are neutron stars, but not all neutron stars are pulsars.
Answer: TRUE
8) Neutron stars are the densest objects that we can observe in the universe.
Answer: TRUE
) No visible light can escape a black hole, but things such as gamma rays, X rays, and neutrinos can.
Answer: FALSE
10) Light from white dwarfs shows a gravitational redshift.
Answer: TRUE
All massive-star supernovae leave behind black holes as remnants.
Answer: FALSE
Planets have been detected around a pulsar.
Answer: TRUE
1) A white dwarf is
A) a precursor to a black hole.
B) an
early stage of a neutron star.
C) what most stars become when
they die.
D) a brown dwarf that has exhausted its fuel for
nuclear fusion.
Answer: C
2) A typical white dwarf is
A) as large in diameter as the Sun
but only about as massive as Earth.
B) as massive as the Sun but
only about as large in size as Earth.
C) 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 Jupiter.
Answer: B
4) The maximum mass of a white dwarf is
A) about the mass of our
Sun.
B) limitless; there is no theoretical limit to the maximum
mass of a white dwarf.
C) about 3 times the mass of our
Sun.
D) about 1.4 times the mass of our Sun.
Answer: D
5) 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
Answer: B
6) According to our modern understanding, what is a nova?
A) an
explosion on the surface of a white dwarf in a close binary system
B) the explosion of a massive star at the end of its life
C) the sudden formation of a new star in the sky
D) a rapidly spinning neutron star
Answer: A
7) Suppose that a white dwarf is gaining mass through accretion in a
binary system. What happens if the mass someday reaches the 1.4 solar
mass limit?
A) The white dwarf will collapse in size, becoming a
neutron star.
B) The white dwarf will undergo a nova explosion.
C) The white dwarf will explode completely as a white dwarf
supernova.
D) The white dwarf will collapse to become a black hole.
Answer: C
8) A neutron star is
A) the remains of a star that died by
expelling its outer layers in a planetary nebula.
B) a star made
mostly of elements with high atomic mass numbers, so that they have
lots of neutrons.
C) the remains of a star that died in a massive
star supernova (if no black hole was created).
D) an object that
will ultimately become a black hole.
Answer: C
9) A typical neutron star is more massive than our Sun and about the
size (radius) of
A) a small asteroid (10 km in
diameter).
B) Earth.
C) the Moon.
D) Jupiter.
Answer: A
11) Pulsars are thought to be
A) accreting white dwarfs.
B)
rapidly rotating neutron stars.
C) unstable high-mass
stars.
D) accreting black holes.
Answer: B
12) How is an X-ray burst (in an X-ray binary system) similar to a
nova?
A) Both involve explosions on the surface of stellar
corpse.
B) Both typically recur every few hours to every few
days.
C) Both are thought to involve fusion of hydrogen into
helium.
D) Both result in the complete destruction of their host stars.
Answer: A
13) What is the basic definition of a black hole?
A) a dead
star that has faded from view
B) any object made from dark
matter
C) an object with gravity so strong that not even light
can escape
D) a compact mass that emits no visible light
Answer: C
14) Based on current understanding, the minimum mass of a black hole
that forms during a massive star supernova is roughly
A) 0.5
solar masses.
B) 1.4 solar masses.
C) 3 solar
masses.
D) 10 solar masses.
Answer: C
15) What do we mean by the event horizon of a black hole?
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.
Answer: D
16) 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 almost instantly be sucked into
oblivion in the black hole.
B) Earth would orbit faster, but at
the same distance.
C) Earth would slowly spiral inward until it
settled into an orbit about the size of Mercury's current orbit.
D) Nothing—Earth's orbit would remain the same.
Answer: D
18) What makes us think that the star system Cygnus X-1 contains a
black hole?
A) It emits X rays characteristic of an accretion
disk, but the unseen star in the system is too massive to be a neutron
star.
B) No light is emitted from this star system, so it must
contain a black hole.
C) The fact that we see strong X-ray
emission tells us that the system must contain a black hole.
D)
Cygnus X-1 is a powerful X-ray burster, so it must contain a black hole.
Answer: A
19) The Schwarzschild radius of a black hole depends on
A) the
observationally measured radius of the black hole.
B) the way in
which the black hole formed.
C) only the mass of the black
hole.
D) both the mass and chemical composition of the black hole.
Answer: C
20) Scientists have detected thousands of gamma ray bursts. The
evidence suggests that most or all of these bursts
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.
Answer: B
21) 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) The life of a white dwarf is an ongoing
battle between electron degeneracy pressure and neutron degeneracy
pressure.
D) In a black hole, the pressure coming from neutron
degeneracy pressure is slightly greater than that coming from electron
degeneracy pressure.
Answer: A
1) Which of the following statements about degeneracy pressure is not
true?
A) Degeneracy pressure can continue to support an object
against gravitational collapse even if the object becomes extremely
cold.
B) Degeneracy pressure arises from a quantum mechanical
effect that we don't notice in our daily lives.
C) Black holes
form when gravity overcomes neutron degeneracy pressure.
D)
Degeneracy pressure can arise only from interactions among electrons.
Answer: D
2) The more massive a white dwarf, the
A) higher its
temperature.
B) smaller its radius.
C) larger its
radius.
D) higher its luminosity.
Answer: B
3) Which of the following best describes why a white dwarf cannot
have a mass greater than the 1.4-solar-mass limit?
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.
Answer: A
4) The white dwarf that remains when our Sun dies will be mostly made
of
A) hydrogen.
B) helium.
C) carbon.
D) neutrons.
Answer: C
5) Which statement about accretion disks is not true?
A) The
gas in the inner parts of the disk travels faster than the gas in the
outer parts of the disk.
B) The gas in the inner parts of the
disk is hotter than the gas in the outer parts of the disk.
C)
The primary factor determining whether a white dwarf has an accretion
disk is the white dwarf's mass.
D) Accretion disks are made
primarily of hydrogen and helium gas.
Answer: C
6) According to present understanding, a nova is caused by
A)
hydrogen fusion on the surface of a white dwarf.
B) carbon fusion
in the core of a white dwarf.
C) hydrogen fusion on the surface
of a neutron star.
D) a white dwarf that gains enough mass to
exceed the 1.4-solar-mass limit.
Answer: A
7) Which of the following is not true about differences between novae
and supernovae?
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.
Answer: B
8) Will our Sun ever undergo a white dwarf supernova explosion? Why
or why not?
A) Yes, right at the end of its double-shell burning
stage of life.
B) Yes, about a million years after it becomes a
white dwarf.
C) No, because it is not orbited by another star.
D) No, because the Sun's core will never be hot enough to fuse
carbon and other heavier elements into iron.
Answer: C
10) 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?
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.
Answer: D
11) Which statement about pulsars is not thought to be true?
A)
All pulsars are neutron stars, but not all neutron stars are pulsars.
B) Pulsars can form only in close binary systems.
C) A
pulsar must have a very strong magnetic field and rotate quite
rapidly.
D) Pulsars are kept from collapsing by neutron
degeneracy pressure.
Answer: B
12) How does an accretion disk around a neutron star differ from an
accretion disk around a white dwarf?
A) The accretion disk
around a neutron star is made mostly of helium while the accretion
disk around a white dwarf is made mostly of hydrogen.
B) The
accretion disk around a neutron star is more likely to give birth to
planets.
C) The accretion disk around a neutron star is much
hotter and emits higher-energy radiation.
D) The accretion disk
around a neutron star always contains much more mass.
Answer: C
13) Which statement concerning black hole masses and Schwarzschild
radii is not true?
A) In a binary system with a black hole, the
Schwarzschild radius depends on the distance from the black hole to
the companion star.
B) The more massive the black hole, the
larger the Schwarzschild radius.
C) Even an object as small as
you could become a black hole if there were some way to compress you
to a size smaller than your Schwarzschild radius.
D) For black
holes produced in massive star supernovae, Schwarzschild radii are
typically a few to a few tens of kilometers.
Answer: A
14) Suppose you drop a clock toward a black hole. As you look at the
clock from a high orbit, what will you notice?
A) Time on the
clock will run faster as it approaches the black hole, and light from
the clock will be increasingly blueshifted.
B) 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.
C)
The clock will fall faster and faster, reaching the speed of light as
it crosses the event horizon.
D) Time on the clock will run
slower as it approaches the black hole, and light from the clock will
be increasingly redshifted.
Answer: D
17) Which of the following observatories is most likely to discover a
black hole in a binary system?
A) the Hubble Space Telescope
B) the Chandra X-Ray Observatory
C) the SOFIA airborne
infrared observatory
D) the Arecibo Radio Observatory
Answer: B
18) Which of the following statements about gamma ray bursts is not
true?
A) Gamma ray bursts are among the most luminous events
that ever occur in the universe.
B) The events responsible for
gamma ray bursts apparently produce only gamma rays, and no other
light that we can hope to detect.
C) Gamma ray bursts were
originally discovered by satellites designed to look for signs of
nuclear bomb tests on Earth.
D) Based on their distribution in
the sky, we can rule out a connection between gamma ray bursts and
X-ray binaries in the Milky Way Galaxy.
Answer: D
19) Imagine an advanced civilization living on a planet orbiting at a
distance of 10 AU (1.5 billion kilometers) from a close binary star
system that consists of a 15 MSun red giant star and a 10 MSun black
hole. The black hole is surrounded by an accretion disk. Sometime
within the next million years or so, the civilization's planet is
likely to be doomed because
A) the red giant will probably
supernova within the next million years.
B) jets of material shot
out of the accretion disk will shoot down their planet.
C) the
red giant star, which provides most of energy the civilization needs
to exist, will soon be destroyed in the accretion disk.
D) tidal
forces from the black hole will rip the planet apart.
Answer: A
20) Consider again the civilization described in the previous
question. (They live on a planet orbiting 10 AU from a close binary
star system that consists of a 15 MSun red giant star and a 10 MSun
black hole surrounded by an accretion disk.) One foolhardy day, a
daring individual in their space force (let's call him Major Tom)
decides to become the first of his species 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 to start the process of
killing him first)?
A) tidal forces due to the black hole
B) X rays from the accretion disk
C) the crush of gravity
at the singularity embedded within the black hole
D) the sucking
force from the black hole, which will cause his head to explode
Answer: B
21) Consider again the civilization described in the previous
question. (They live on a planet orbiting 10 AU from a close binary
star system that consists of a 15 MSun red giant star and a 10 MSun
black hole surrounded by an accretion disk.) Through a bizarre (and
scientifically unexplainable) fluctuation in the space-time continuum,
a copy of a book from that civilization arrives on your desk; it is
entitled Iguoonos: How We Evolved. In the first chapter, you learn
that these beings 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?
A) As a result of traumatic
experiences to their evolutionary ancestors, they dislike television.
B) Their immediate ancestors were chimpanzees.
C) They
believe that the presence of two stars in their system was critical to
their evolution.
D) 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.
E)
They evolved on a different planet in a different star system, and
moved to their current location.
Answer: E