TEST BANK 21ST CENTURY
ASTRONOMY THE SOLAR SYSTEM 5TH EDITION BY KAY
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Chapter 15: Star Formation and the Interstellar Medium
Learning Objectives.
Define the bold-faced vocabulary terms within the chapter.
15.1 The Interstellar Medium Fills the
Space between the Stars
Describe
the observational signatures of interstellar dust.
Multiple
Choice: 2, 13, 14, 15, 16, 17, 18
Short
Answer: 3
Differentiate between interstellar extinction and reddening.
Multiple
Choice: 33
Short
Answer: 7
Compare and contrast the densities and temperatures of the
gas components of the interstellar medium.
Multiple
Choice: 1, 3, 4, 6, 7, 10, 11, 12, 20, 21, 28, 29, 31
Short
Answer: 1, 2, 4, 10, 11, 13, 14
Describe the observational signatures of each gas component
of the interstellar medium.
Multiple
Choice: 5, 8, 22, 23, 24, 25, 26, 27, 30, 32
Short
Answer: 5, 6, 8, 9
15.2 Molecular Clouds Are the Cradles of
Star Formation
Describe
the process of fragmentation during the collapse of a cloud.
Multiple
Choice: 35, 36, 37, 39, 40, 41, 42, 43
Short
Answer: 15, 16
Evaluate why molecular clouds are the cradles of star
formation.
Multiple
Choice: 34, 38
Short
Answer: 17, 18
15.3 Formation and Evolution of Protostars
Explain
why conversion of gravitational to thermal energy heats a collapsing gas.
Multiple
Choice: 47
Short
Answer: 20, 21, 23
Describe how hydrostatic equilibrium supports a
self-gravitating object.
Illustrate
the chain of events leading from molecular cloud to protostar.
Multiple
Choice: 9, 44, 45, 48, 53
Short
Answer: 19
Distinguish between the conditions under which a protostar
becomes a star and a brown dwarf.
Multiple
Choice: 49, 50, 51, 52
Short
Answer: 22
15.4 Evolution before the Main Sequence
Describe
how the H−
ion acts as a natural thermostat for a star.
Multiple
Choice: 54
Short
Answer: 24
Explain why a protostar’s temperature rises but its
luminosity drops as it settles onto the main sequence.
Multiple
Choice: 46, 55, 56, 57, 58, 59, 60, 62, 64
Short
Answer: 25
Illustrate the observational features and possible origins of
bipolar outflows.
Multiple
Choice: 67, 68
Short
Answer: 26
Establish why a protostar’s mass influences the rate at which
it collapses to become a star.
Multiple
Choice: 61, 63, 65, 66, 69
Short
Answer: 28
Describe the conditions necessary for planets to form around
protostars.
Multiple
Choice: 70
Short
Answer: 30
Working It Out 15.1
Compute
the peak wavelength of emission from dust grains.
Multiple
Choice: 19
Short
Answer: 12
Working It Out 15.2
Use
the blackbody luminosity, temperature, and size
relationship to relate how changing a protostar’s size changes its luminosity.
Short
Answer: 27, 29
MULTIPLE CHOICE
1.
The average density of the interstellar
medium is
a. much
denser than the Earth’s atmosphere.
b. much
less dense than the best vacuum on Earth.
c. about
the same density as air on the peak of Mount Everest.
d. zero.
2.
The dust in the interstellar medium comes
primarily from
a. the
stellar winds of main-sequence stars.
b. the
cooled material ejected from supernova explosions.
c. cold
cores of molecular clouds.
d. all
of the above
3.
The lowest-density gas in the interstellar
medium is also the
a. coldest.
b. least
ionized.
c. hottest.
d. most
localized, being found mostly around protostars.
4.
The interstellar medium is divided up into
three different kinds of gas clouds. These are
a. cold
gas at 100 K, warm gas at 8000 K, and hot gas at about 1 million K.
b. warm
gas at 8000 K, hot gas at 1 million K, and superhot gas at 10 million K.
c. warm
gas at 5000 K, warm-hot gas at 100,000 K, and hot gas at about 1 million K.
d. cold
gas at 100 K, cool gas at 1000 K, and warm gas at 8000 K.
5.
We observe neutral hydrogen gas using
a. X-ray
radiation from highly ionized atoms.
b. visible
radiation at 656.3 nm from re-combined hydrogen.
c. 21-cm
emission.
d. ultraviolet
radiation from helium and oxygen.
6.
Molecular hydrogen atoms are found
a. everywhere
throughout interstellar space.
b. only
in dense clouds where they are shielded from stellar radiation.
c. in
low density clouds of hot gas surrounding hot stars.
d. only
in the atmospheres of the giant planets, such as Jupiter.
7. The
coldest molecular clouds in our galaxy have temperatures of approximately
a. 1000
K.
b. 100
K.
c. 10
K.
d. 0
K.
8. Electronic
transitions from the H2 molecule are easily seen at
a. X-ray
wavelengths.
b. visible
wavelengths.
c. radio
wavelengths.
d. infrared
wavelengths.
9. If
you could watch stars forming out of a gas cloud, which stars would form first?
a. low-mass
stars
b. medium-mass
stars
c. high-mass
stars
d. stars
with low temperatures
e. stars
with more heavy elements
10. When
looking at the space between stars, what might you see?
a. nothing;
it is empty.
b. spacecraft
c. gas
d. dark
matter
e. none
of the above
11. The
average density of the interstellar medium is
a. 1
atom/cm3.
b. 1,000
atom/cm3.
c. 104
atom/cm3.
d. 106
atom/cm3.
e. 1012
atom/cm3.
12. If
you wanted to observe heavy elements in the interstellar medium, where would be
the best place to look?
a. dust
grains
b. cold
gas
c. hot
gas
d. warm
gas
13. When
radiation from an object passes through the interstellar medium,
a. the
object appears dimmer.
b. the
object appears bluer.
c. the
object appears bluer and dimmer.
d. the
object appears redder and dimmer.
e. the
object’s apparent velocity changes.
14. Dust
in the ISM appears dark in _________ wavelengths and bright in _________
wavelengths.
a. visible;
ultraviolet
b. infrared;
radio
c. infrared;
visible
d. radio;
ultraviolet
e. visible;
infrared
15. Dust
reddens starlight because it
a. re-emits
the light it absorbs at red wavelengths.
b. emits
mostly in the infrared due to its cold temperature.
c. is
made mostly of hydrogen, which produces the red H-alpha emission line.
d. preferentially
affects light at visible and shorter wavelengths.
e. primarily
moves away from Earth.
16. What
is the most likely explanation for the dark area in the figure shown below?
a. It
is a region where there are no stars.
b. It
is a region with lots of dark matter.
c. It
is a super-massive black hole.
d. It
is a region with thick dust blocking the starlight coming from behind.
e. It
is a dark star cluster.
17. The
figure below shows the spectrum of a star, along with five other spectra
labeled A through E. Which one of the labeled spectra shows what the spectrum
of that star would look like if it were viewed through a significant amount of
interstellar dust?
a. A
b. B
c. C
d. D
e. E
18. The
figure below shows three pictures of the disk of the Milky Way, taken in three
different wavelength ranges. Put the three pictures in order from shortest to
longest wavelength.
a. I,
II, III
b. II,
III, I
c. I,
III, II
d. II,
I, III
e. III,
I, II
19. Dust
that is heated to 30 K will emit a blackbody spectrum that peaks at
a. 1
µm.
b. 30
µm.
c. 50
µm.
d. 100
µm.
e. 500
µm.
20. Sitting
in a 100°F hot tub feels much hotter than standing outside on a 100°F day. This
analogy illustrates why
a. interstellar
dust is dark at optical wavelengths but bright in the infrared.
b. supernovae
can heat their shells to such high temperatures.
c. an
astronaut would feel cold standing in the 106 K intercloud gas.
d. the
Solar System is immersed in a hot bubble of gas.
e. fusion
occurs only in the cores of stars.
21. Which
of the following is responsible for heating the bulk of the very hot intercloud
gas?
a. high-energy
radiation from stars
b. supernovae
c. young
O and B stars
d. planetary
nebulae
e. The
heating is an even mix of all of the sources above.
22. Warm
ionized gas in the interstellar medium appears _________ when imaged in the
optical region of the electromagnetic spectrum.
a. red
b. yellow
c. white
d. blue
e. dark
23. The
red emission in the figure shown below is due to
a. carbon
monoxide (CO).
b. warm,
neutral hydrogen.
c. molecular
hydrogen (H2).
d. ionized
hydrogen (H II region).
e. dust.
24. An
H II region signals the presence of
a. newly
formed stars.
b. young
stars.
c. ionized
hydrogen gas.
d. O-
and B-type stars.
e. all
of the above
25. If
you wanted to study regions where star formation is currently happening, you
could use
a. H-alpha
emission to look for O and B stars.
b. 21-cm
radiation to find neutral hydrogen clouds.
c. radio
emission from carbon monoxide (CO) to find molecular cloud cores.
d. infrared
emission to identify T Tauri stars.
e. all
of the above
26. 21-cm
radiation is important because it
a. allows
us to study the deep interiors of stars.
b. allows
us to image magnetic fields directly.
c. allows
us to study neutral hydrogen in the interstellar medium.
d. is
produced by every object in the universe.
e. is
the longest wavelength of light that can naturally be produced.
27. We
detect neutral gas in the interstellar medium by looking for radiation at 21 cm
that arises when
a. an
electron moves from the n = 1 to n = 2 state in a hydrogen atom.
b. an
electron is ionized from a hydrogen atom.
c. carbon
monoxide (CO) gas is excited by stellar radiation.
d. the
spin of an electron flips and aligns with the spin of a proton in a hydrogen
atom.
e. an
electron combines with a proton to make a hydrogen atom.
28. In
the interstellar medium, molecules survive only in regions with
a. low
temperatures.
b. high
densities.
c. lots
of dust.
d. all
of the above
29. Interstellar
clouds are
a. hydrogen
gas, condensed out of the interstellar medium, like water clouds in the Earth’s
atmosphere.
b. regions
where hydrogen tends to be denser than the surrounding gas.
c. regions
where water condenses out of the interstellar medium.
d. oxygen
gas, condensed out of the interstellar medium, like water clouds in the Earth’s
atmosphere.
e. regions
where hydrogen combines with oxygen to create water molecules.
30. What
primarily makes it difficult to observe the process of star formation?
a. They
occur in dusty regions.
b. They
have low luminosities.
c. They
do not shine at any wavelength until they become T Tauri stars.
d. The
star formation process happens so quickly.
e. They
are too small to be seen.
31. A
typical molecular cloud has a temperature of approximately
a. 0.3
K.
b. 10
K.
c. 80
K.
d. 300
K.
e. 1000
K.
32. Molecular
clouds, which have temperatures of around 10 K, are best observed at _________
wavelengths.
a. X-ray
b. ultraviolet
c. optical
d. infrared
e. radio
33. Interstellar
extinction compared to interstellar reddening is like _______ as opposed to
_______
a. viewing
the Sun through a fog in Earth’s atmosphere; viewing the Sun through a cloud of
haze from a forest fire.
b. viewing
the Sun through a cloud of haze from a forest fire; viewing the Sun looking
outward from underwater.
c. viewing
the Sun through a cloud of haze from a forest fire; viewing the Sun through a
fog in Earth’s atmosphere.
d. viewing
the Sun looking outward from underwater; viewing the Sun through a prism.
34. Molecular
cloud cores are places where you might find
a. protostars
b. Herbig-Haro
objects.
c. molecular
hydrogen (H2).
d. carbon
monoxide (CO).
e. all
of the above
35. For
an object in hydrostatic equilibrium, if the temperature inside the object were
to increase, the object would
a. expand.
b. contract.
c. implode.
d. remain
the same size.
e. explode.
36. Because
angular momentum must be conserved, as a gas cloud contracts due to gravity it
will also
a. spin
slower.
b. spin
faster.
c. increase
in temperature.
d. decrease
in temperature.
e. stay
the same temperature.
37. Star
formation in a molecular cloud can be slowed by
a. the
presence of dust.
b. the
strength of its magnetic field.
c. turbulence
caused by supernovae and stellar winds from massive stars.
d. all
of the above
38. Stars
forming in molecular clouds tend to form first in
a. the
low-density periphery.
b. the
high-density core.
c. random
locations.
d. any
location where the temperature is highest.
39. Of
the following processes at work in molecular clouds, which is the one that
inevitably dominates the clouds’ evolution?
a. magnetic
fields
b. conservation
of angular momentum
c. pressure
d. gravity
e. turbulence
40. Magnetic
fields inside a molecular cloud act to
a. inhibit
gravitational collapse.
b. fragment
the cloud into numerous cores.
c. modulate
the temperature of the molecules.
d. increase
the formation of dust grains.
e. increase
the formation of protostars.
41. The
entire process of star formation is really just an evolving balance between
a. heat
and rotation.
b. core
temperature and surface temperature.
c. pressure
and gravity.
d. radiation
and heat.
e. luminosity
and distance.
42. Which
of the following traits does not
help slow or prevent the collapse of a gas cloud?
a. high
mass
b. high
temperature
c. turbulence
d. magnetic
fields
e. angular
momentum
43. An
accretion disk forms around a collapsing protostar because infalling material
must conserve
a. energy.
b. centrifugal
force.
c. gravity.
d. velocity.
e. angular
momentum.
.
44. As
a protostar evolves, its temperature
a. decreases
because it is radiating.
b. decreases
because of gravitational contraction.
c. decreases
because of angular momentum.
d. increases
because of nuclear fusion.
e. increases
due to the kinetic energy of infalling material.
45. A
protostar is
a. in
hydrostatic equilibrium as it collapses.
b. far
out of hydrostatic equilibrium when it collapses.
c. heated
to millions of degrees as it collapses.
d. flattened
into a disk as it collapses.
46. A
young protostar is _________ than the Sun even though its surface temperature
is _________
a. less
luminous; hotter.
b. larger;
cooler.
c. smaller;
the same.
d. more
luminous; cooler.
e. smaller;
hotter.
47. The
source of energy for a contracting protostar comes from
a. thermonuclear
energy.
b. kinetic
energy.
c. chemical
energy.
d. gravitational
potential energy.
e. radiation
energy.
48. What
happens as a protostar contracts?
a. Its
density rises.
b. Its
temperature rises.
c. Its
radius decreases.
d. Its
pressure rises.
e. All
of the above are true.
49. What
critical event transforms a protostar into a normal main-sequence star?
a. Planets
form in the accretion disk.
b. The
star grows suddenly larger in radius.
c. Triple
alpha reactions begin in the core.
d. Nuclear
fusion begins in the core.
e. Convection
begins throughout the star’s interior.
50. Stars
with a mass from 0.01 M⊙ to 0.08 M⊙ are
very different from the Sun because they
a. do
not have strong enough gravity to form planets.
b. have
much higher temperatures than the Sun.
c. cannot
successfully execute the proton-proton chain reactions.
d. form
much faster than the Sun did.
e. do
not exhibit sunspots.
51. A
_________ is a failed star that shines primarily because of energy derived from
its gravitational collapse rather than nuclear burning.
a. black
hole
b. brown
dwarf
c. Herbig-Haro
object
d. protostar
e. T
Tauri star
52. Brown
dwarfs are considered failed stars because
a. they
never reach masses larger than 50 Jupiter masses.
b. hydrogen
fusion never begins in their cores.
c. convection
never plays a role in their energy transport.
d. they
shine primarily at infrared wavelengths.
e. they
are never as luminous as the Sun.
53. The
H−
atom is important in protostars because it acts as a
a. source
of friction, stopping the cloud from collapsing too rapidly.
b. source
of infrared radiation, causing the cloud to cool off rapidly.
c. temperature
regulator.
d. source
of buoyancy, allowing the atmosphere of the protostar to expand.
54. The
H−
ion is very important in protostars because it
a. reacts
with oxygen to produce water.
b. undergoes
fusion and produces energy.
c. helps
make the protostars denser.
d. acts
as a temperature regulator.
e. reduces
angular momentum.
55. A
protostar’s evolutionary “track” in the H-R diagram traces out
a. only
how the protostar’s radius changes with time.
b. how
the protostar’s luminosity, temperature, and radius change with time.
c. only
how the protostar’s luminosity changes with time.
d. only
how the protostar’s spectral type changes with time.
e. the
protostar’s location in the molecular cloud.
56. The
Hayashi track of a low-mass protostar in the H-R diagram is a path of
approximately constant
a. density.
b. luminosity.
c. age.
d. temperature.
e. radius.
57. Use
the figure shown below to complete the following statement. A high-mass
protostar remains roughly constant in _________ and increases in _________ as
it follows its evolutionary track.
a. temperature;
luminosity
b. radius;
temperature
c. luminosity;
radius
d. luminosity;
temperature
e. radius;
luminosity
58. Use
the figure shown below to complete the following statement. A low-mass
protostar remains roughly constant in _________ and decreases in _________ as
it follows its evolutionary track.
a. temperature;
luminosity
b. radius;
temperature
c. luminosity;
radius
d. luminosity;
temperature
e. radius;
luminosity
59. Use
the figure shown below to complete the following statement. At the start of the
evolution of a protostar, the radius of a 60 M⊙ protostar is roughly _________ that of a 1 M⊙ main-sequence star.
a. 10
times bigger than
b. 100
times bigger than
c. 10
times smaller than
d. 100
time smaller than
e. the
same as
60. Use
the figure shown below to complete the following statement. As a protostar
contracts,
a. the
luminosity decreases.
b. the
luminosity increases.
c. the
temperature increases.
d. the
temperature decreases.
e. either
the luminosity decreases or the temperature increases.
61. Star
formation is an inefficient process, with only a few percent of the initial
cloud fragment ending up as stars. This means the initial mass of a molecular
cloud fragment that formed a 2 M⊙ star
was probably close to
a. 1
M⊙.
b. 50
M⊙.
c. 100
M⊙.
d. 5000
M⊙.
e. 1,000,000
M⊙.
62. If
a 1 M⊙ protostar starts out on the Hayashi track with
a temperature of 3300 K and a luminosity of 320 L⊙, what is its
approximate radius?
a. 5
R⊙
b. 50
R⊙
c. 100
R⊙
d. 200
R⊙
e. 500
R⊙
63. Which
of the following stars spend the longest time on their Hayashi tracks?
a. 100
M⊙ stars
b. 10
M⊙ stars
c. 1
M⊙ stars
d. 0.1
M⊙ stars
e. 0.08
M⊙ stars
64. A
surprising fact about a 1 M⊙ protostar is that, even though nuclear
reactions have not yet started in their cores, they are _________ than the Sun
a. hotter
b. rotating
faster
c. smaller
d. denser
e. more
luminous
65. How
long does it typically take for a protostar to form a 1 M⊙ star?
a. 3
× 107 years
b. 3
× 105 years
c. 3,000
years
d. 300
years
e. 30
years
66. The
most common types of stars in our galaxy are
a. high-mass
stars.
b. low-mass
stars.
c. an
equal mix of high- and low-mass stars.
d. low-mass
stars near the Sun and high-mass stars far away.
e. We
do not yet know which types of stars are most common in our galaxy.
67. Herbig-Haro
objects are almost always found
a. in
pairs on either side of a young protostar.
b. far
away from molecular clouds where stars form.
c. close
to planets that are forming around protostars.
d. deep
inside molecular clouds.
68. When
winds blow the gas away from a forming protostar, the protostar
a. expands
rapidly to 100 times its original size.
b. is
revealed as a main-sequence star.
c. becomes
visible as a T Tauri star.
d. is
unable to reach the main sequence.
69. When
a molecular cloud fragments,
a. the
least massive stars are the first to form, while the most massive stars take
longer.
b. the
most massive star are the first to form, while the least massive star take
longer.
c. the
most massive stars promptly explode as supernovae, destroying all remaining
gas.
d. the
stars form at the same rate, regardless of their mass.
70. Where
have astronomers observed the existence of planets?
a. in
our Solar System
b. orbiting
stars other than the Sun
c. orbiting
stars in binary systems
d. traveling
on their own through the Milky Way, not orbiting a star
e. all
of the above
SHORT ANSWER
1.
Compare the volume of the Sun with the
volume of interstellar space it occupies. Is the occupied percentage large or
small? Consider the volume around the Sun to be a sphere whose radius is equal
to the distance to the nearest star, which is equal to 5 light-years. (Note:
the radius of the Sun is 7 ×
105 km, and 1 light-year = 9.5 × 1012 km.)
2.
What is the interstellar medium made of?
Give rough percentages of each.
3.
Why can we see dust in the interstellar
medium better at far-infrared wavelengths than we can at optical wavelengths?
4.
How are H II regions and the hot intercloud
gas heated?
5.
How are each of the following types of ISM
detected by astronomers: hot intercloud gas, H II regions, neutral hydrogen
gas, and molecular clouds.
6.
At what wavelength are H II regions most
clearly visible, and why do H II regions mark the regions where new stars are
currently being formed?
7.
What is the difference between interstellar
extinction and interstellar reddening?
8.
Suppose the 21-cm photon of neutral hydrogen
were instead emitted at 500 nm (i.e., a visible blue photon). Would it still be
a useful probe of the Milky Way’s structure? Why?
9.
Why do H II regions mark the regions where
new stars are currently being formed?
10. How
are typical interstellar gas clouds different from the clouds that we see in
the Earth’s sky?
11. Why
do molecules readily exist in Earth’s atmosphere but not in most of
interstellar space?
12. Suppose
we observe two molecular clouds containing dust. The dust in Cloud 1 peaks in
emission at 50 mm, while the dust in Cloud 2 peaks in emission at 78 mm. How
much warmer is the dust in Cloud 1 compare to Cloud 2?
13. In
the densest molecular clouds, the average density is approximately 300 atoms/cm3.
If a cube of molecular cloud gas with this density contained 100 M⊙ of
material (the amount needed to make a 1 M⊙ star), what would be the length of a side of
the cube in units of AU? For reference, the mass of the Sun is 2 × 1030 kg,
the mass of a hydrogen atom is 1.7 × 10−27
kg, and 1 AU =
1.5 × 1011 m.
14. Why
is it possible for self-gravity to dominate pressure in molecular clouds but
not in most interstellar clouds?
15. Some
molecular clouds have so much internal pressure that it exceeds their
self-gravity. What keeps them from expanding and dissipating?
16. Why
do molecular clouds collapse from the inside out?
17. Why
do many stars form from a single molecular cloud?
18. Why
do stars form most often within molecular clouds?
19. Describe
the general process of how the interstellar medium can create a star.
20. Why
can’t very bright protostars be seen in visible light?
21. Why
does a protostar continue to collapse as it is forming?
22. What
is the energy source that powers brown dwarf stars?
23. Explain
why a star of higher mass must have a higher core temperature.
24. Why
does the surface temperature of a low-mass protostar remain nearly constant as
its core contracts?
25. In
the figure shown below, the portion of the H-R diagram corresponding to the
Hayashi track of a 1 M⊙ star is shown. Temperature increases toward
the right, and luminosity increases toward the top of the diagram. Even though
the temperature of the protostar is hardly changing as it approaches the main
sequence, its luminosity is decreasing. Why?
26. How
are Herbig-Haro objects related to T Tauri stars?
27. When
a 3 M⊙ protostar forms, it starts out at the top of
the Hayashi track with a luminosity of 4,000 L⊙ and a
temperature of 3600 K. What is its radius at this point (give the answer in
units of R⊙),
and how many times larger is it at this stage compared to its radius as a
main-sequence star, which is about 2.5 R⊙? For reference, the Sun’s temperature is
5800 K.
28. Astronomers
cannot observe the entire process of star formation during a human lifetime.
What property of star clusters allows them to circumvent much of this problem?
29. Suppose
a protostar shrinks in size from 100 R⊙ down to 20 R⊙,
while maintaining a constant temperature. By what factor does its luminosity
decrease?
30. Name
four conditions necessary for planets to exist with conditions suitable for
life.
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assignments, plagiarism free and to custom requirement.
We will always meet deadlines.
Our support will be 24/27, even
in holidays.
Our pricing will be fair.
We will do free revisions if
you want to make changes in provided work.
Email us for more information,
query and quote.
WHISPERHILLS@GMAIL.COM
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