TEST BANK 21ST CENTURY ASTRONOMY THE SOLAR SYSTEM 5TH EDITION BY KAY
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Chapter 23: Large-Scale
Structure in the Universe
Learning
Objectives
Define the boldfaced vocabulary terms within the chapter.
23.1 Galaxies Form Groups, Clusters, and
Larger Structures
Compare and contrast groups, clusters, superclusters, and
walls.
Multiple Choice: 1, 2, 3, 4, 6, 7, 9, 10, 13, 18
Short Answer: 1, 8
Summarize the evidence for dark matter dominating the mass of
groups and clusters.
Multiple Choice: 12, 14, 15, 16, 17
Short Answer: 2, 3, 4, 5, 7
Describe how Hubble’s law helps astronomers map the structure
of mass in the universe.
Multiple Choice: 5, 8, 11
Short Answer: 6
23.2 Gravity Forms Large-Scale Structure
Illustrate the steps that led to large-scale structure
formation.
Multiple Choice: 20, 21, 26, 37, 38
Describe how gravitational instabilities created the seeds of
large-scale structure.
Multiple Choice: 19, 22, 23, 29, 36
Short Answer: 11
Relate the presence of dark matter to the formation of
galaxies in the early universe.
Multiple Choice: 24, 25, 34, 39
Short Answer: 14
Summarize the observational evidence that dark matter cannot
be composed of ordinary matter.
Multiple Choice: 27, 30, 33, 35
Compare and contrast the properties and possible constituents
of cold and hot dark matter.
Multiple Choice: 28, 31, 32
Short Answer: 9, 15, 16
Describe the collapse of cold dark matter into a galaxy halo
after recombination.
Short Answer: 10
23.3 First Light of Stars and Galaxies
Describe the properties of the very first generation of stars
and whether these are based on observations or hypotheses.
Multiple Choice: 44, 47, 48, 52
Short Answer: 24
Explain why the first generation of stars were expected to be
very massive, while subsequent generations could have high and low mass.
Multiple Choice: 45, 53, 54
Short Answer: 25, 28
Describe the properties of the first generation of galaxies
and whether these are based on observations or hypotheses.
Multiple Choice: 46, 49, 55
Short Answer: 12, 13, 27
Compare and contrast the processes of star and galaxy
formation.
Multiple Choice: 50, 51
Short Answer: 23, 26
23.4 Galaxies Evolve
Describe the hierarchical formation scenario that built up
fragments into today’s galaxies.
Short Answer: 29
Summarize the observational evidence that galaxies formed by
hierarchical merging.
Multiple Choice: 57, 65, 67, 68
Short Answer: 32
Relate the formation of supermassive black holes to galaxy
evolution and star-formation rates.
Multiple Choice: 58, 66, 69, 71, 73
Compare and contrast the results of cosmological simulations
to measurements of cosmic structure.
Multiple Choice: 59, 60, 63, 64, 70
Short Answer: 30, 31
Describe the expected stages of future evolution of our
universe.
Multiple Choice: 56, 61, 62, 72
Working It Out 23.1
Use orbital properties of galaxies to calculate their mass.
Working It Out 23.2
Calculate the observed wavelength of highly redshifted light.
Multiple Choice: 40, 41, 42, 43
Short Answer: 17, 18, 19, 20, 21, 22
MULTIPLE CHOICE
1.
Which of these shows
the correct order of collections of galaxies, starting with the smallest and
ending with the largest?
a.
group, supercluster,
cluster
b.
cluster, supercluster,
group
c.
group, cluster,
supercluster
d.
cluster, group,
supercluster
e.
supercluster, group,
cluster
2.
The most common type of
galaxy found in a galaxy cluster is a ___________ galaxy.
a.
spiral
b.
giant elliptical
c.
giant irregular
d.
dwarf
e.
barred spiral
3.
What does the
large-scale structure of the universe look most like?
a.
a sponge with many
large holes
b.
a loaf of wheat bread
with many tiny holes
c.
a plate of flat noodles
d.
a jar of marbles
e.
a pizza with evenly
distributed pepperoni
4.
What is our cosmic
address?
a.
Earth, Solar System,
Milky Way, Local Group, Laniakea Supercluster
b.
Earth, Solar System,
Andromeda, the Great Attractor, Local Group
c.
Earth, Local Group,
Solar System, Milky Way, Cosmic Microwave Background
d.
Earth, Local Group,
Solar System, Milky Way, Laniakea Supercluster
e.
Earth, Solar System,
Andromeda, the Great Attractor, Laniakea Supercluster
5.
Peculiar velocities are
produced by
a.
erroneous redshifts.
b.
gravity.
c.
supernovae.
d.
eclipsing binary stars.
e.
interstellar winds.
6.
The most common galaxy
collections are called _______ and most of their members are _______ galaxies.
a.
clusters; spiral
b.
groups; dwarf
c.
superclusters;
elliptical
d.
voids; peculiar
e.
walls; lenticular S0
7.
How many times would
our Local Group fit along the distance that separates it from the Virgo
Cluster?
a.
5
b.
10
c.
200
d.
1000
e.
2
8.
Understanding the
distribution of galaxies in the universe requires the construction of a 3D map
where for each galaxy we need to know its position and
a.
mass.
b.
redshift.
c.
color.
d.
morphological type.
e.
star formation rate.
9.
The peculiar velocity
of a galaxy describes its motion relative to the
a.
Local Group.
b.
center of the Milky
Way.
c.
center of the universe.
d.
Great Attractor.
e.
cosmic microwave
background.
10.
The figure below shows
a small section of the Virgo galaxy cluster. The indicated galaxy can be
classified as
a.
elliptical.
b.
peculiar.
c.
dwarf.
d.
ultrafaint.
e.
quasar.
11.
Virgo galaxy cluster is
at an estimated distance of 54 million ly. What is the average recession speed
of the cluster, assuming a Hubble constant of 70km/s/Mpc?
a.
1,200 km/s
b.
32,000 km/s
c.
300 km/s
d.
10,000 km/s
e.
3800 km/s
12.
Scientists estimate the
following quantities for the Coma cluster of galaxies: the total mass of the
cluster is Mtotal ~ 3.3 × 1015 M⊙, the total mass of all stars Mstars
~ 3 × 1013 M⊙, and the mass of the hot X-ray−emitting gas Mgas ~ 1 × 1014 M⊙. What is corresponding
percentage of dark matter within the Coma cluster?
a.
4 percent
b.
25 percent
c.
72 percent
d.
96 percent
e.
There is no dark matter
contribution.
13.
Which of the following
is not true about the Great Attractor?
a.
It is about 75 Mpc
away.
b.
It has a mass of
several thousand times the mass of the Milky Way.
c.
It is at the center of
the Laniakea supercluster.
d.
It is in fact a black
hole the size of a galaxy.
e.
It has gravitational
effects on the motion of galaxies and groups of galaxies.
14.
Choose the incorrect
statement about the gas that fills the space between galaxies in a cluster?
a.
It is very hot and
glows in X-rays.
b.
Its total mass far
exceeds the combined mass of all the stars in the galaxy members of the
cluster.
c.
Its particles move so
fast that they easily escape the gravity of the cluster.
d.
It originates in
stellar winds and/or it is stripped away from colliding galaxies.
e.
Its temperature gives
us clues about the total gravitational mass of the cluster.
.
15.
Which of the following
does not provide direct evidence for the existence of dark
matter?
a.
the rotation curves of
spiral galaxies
b.
the motions of galaxies
in clusters
c.
the temperature of the
diffuse intergalactic gas within clusters
d.
the gravitational
lensing produced by galaxy clusters
e.
the changing fraction
of peculiar galaxies as a function of redshift
16.
Which of the following
is not a way in which astronomers detect dark matter in clusters
of galaxies?
a.
by determining the
amount of mass necessary to gravitationally collapse clouds of gas to form the
number of stars present
b.
by determining the
amount of mass necessary to gravitationally hold onto the hot gas within galaxy
clusters
c.
by determining the
amount of mass necessary to gravitationally hold a cluster of galaxies together
d.
by determining the amount
of mass necessary to gravitationally lens images of distant objects
e.
None of the above; all
of these are ways that astronomers detect dark matter in galaxy clusters.
17.
Which of the following
components makes up the largest amount of normal matter in a typical large
cluster of galaxies?
a.
supermassive black
holes
b.
stars
c.
cold gas
d.
hot gas
e.
neutron and white dwarf
stars
18.
If a galaxy is a member
of a large cluster of galaxies, like the Coma cluster, the galaxy would have a
typical velocity of 1,000 km/s. If the cluster is 10 Mpc in diameter, how long
would it take the galaxy to cross from one side of the cluster to another?
a.
10,000 years
b.
1 million years
c.
10 million years
d.
100 million years
e.
10 billion years
19.
What has the dominant
role in defining the large-scale structure of the universe?
a.
supernovae from the
first generation of stars
b.
gravity
c.
matter/antimatter
annihilation
d.
magnetic fields
e.
electric force
.
20.
Structure formation in
our universe
a.
occurs for the largest
structures first.
b.
occurs for the smallest
structures first.
c.
begins on all spatial
scales at the same time.
d.
begins after clusters
form.
e.
begins with planets.
21.
Structure formation in
the universe proceeds hierarchically, meaning that
a.
large objects collapse
and then fragment to form smaller objects.
b.
large objects form at
the same times as smaller objects.
c.
small objects collapse
and then merge to form larger objects.
d.
only small objects form
and are stable over time.
e.
normal matter collapses
first and dark matter collapses later.
.
22.
Quantum fluctuations in
the early universe
a.
were the seeds that
grew into today’s galaxies.
b.
are the reason dark
matter exists.
c.
were made of small
black holes.
d.
had no effect on the
current structure of the universe.
e.
can be observed with
radio telescopes.
23.
The “Lambda-CDM” model
combines the properties of __________ to explain the formation of structure in
the universe.
a.
black holes and neutron
stars
b.
dark energy and cold
dark matter
c.
star formation and
angular momentum
d.
nucleosynthesis and hot
dark matter
e.
gravity and nuclear
forces
24.
Our current ideas on
galaxy formation suggest that the visible parts of galaxies
a.
form first and are
incorporated into dark matter halos later.
b.
form only in the
densest parts of dark matter halos.
c.
can tell you the total
size of the dark matter halo.
d.
can tell you everything
about the formation history of that galaxy.
e.
spread out over
distances larger than those of dark matter halos.
25.
Why can’t dark matter
halos collapse to be the same size as the visible parts of galaxies?
a.
Dark matter can’t
dissipate its energy through radiation from collisions.
b.
Dark matter is made
mostly of mini−black holes.
c.
Dark matter has much
more angular momentum.
d.
Dark matter annihilates
when it begins to get that dense.
e.
Dark matter particles
are too large to collapse that much.
26.
The figure below shows
snapshots taken from the Bolshoi simulation of the formation of the large-scale
structure in the universe. Which one of these images shows the current
structure of the universe?
a.
A
b.
B
c.
C
d.
D
e.
All of these occur at
the same redshift, just in different regions of the universe.
27.
Which of the following
is not a possible candidate for dark matter?
a.
axions
b.
positrons
c.
photinos
d.
neutrinos
e.
WIMPS
28.
Scientists think that
neutrinos cannot be the dominant form of dark matter in the universe. Why?
a.
Neutrinos are an
example of hot dark matter that could form large superclusters but not smaller
structures.
b.
Neutrinos interact too
strongly with ordinary matter.
c.
Neutrinos would decay
over time and disappear, causing galaxies to fall apart.
d.
Neutrinos would not
gravitationally lens background galaxies.
e.
Neutrinos are charged
particles.
29.
The small density
variations that subsequently led to the formation of large-scale structure in
the universe are thought to have formed
a.
from quantum
fluctuations during inflation.
b.
due to the supernovae
of the very first stars.
c.
at the end of the
recombination epoch.
d.
as
particle-antiparticle pairs annihilated.
e.
as supermassive black
holes powered the first quasars.
30.
The density of normal
matter in the early universe was ______________ in the present epoch universe.
a.
much higher than the
density of normal matter
b.
much lower than the
density of normal matter
c.
about the same as the
density of normal matter
d.
much higher than the
density of dark matter
e.
about the same as the
density of dark matter
.
31.
Which of the following
is true about neutrinos?
a.
They are an example of
cold dark matter.
b.
They are an example of
hot dark matter.
c.
They have been
theoretically predicted, yet never detected.
d.
They must be much more
massive than the dark matter candidate called photino.
e.
They account for all
the dark matter in the universe.
32.
Which of the following
statements about dark matter is incorrect?
a.
Cold and hot dark
matter play differently on the formation of small and large-scale structure.
b.
Cold dark matter has
the dominant role in the formation of individual galaxies.
c.
Dark matter most likely
consists of elementary particles with no electric charge.
d.
Physicists use particle
accelerators to look for hypothesized dark matter candidates.
e.
Hot dark matter has the
dominant effect in the formation of individual galaxies.
33.
If dark matter
consisted of ordinary particles like protons and neutrons,
a.
the fraction of light
elements produced in the Big Bang nucleosynthesis would have been severely
different from what scientists observe.
b.
it wouldn’t have
affected gravitationally the large scale structure of the universe.
c.
it would have prevented
the expansion of the universe.
d.
scientists would easily
be able to measure the decay of proton in the lab.
e.
it would manifest
differently in individual galaxies and in large superclusters of galaxies.
34.
Dark matter is
essential in understanding the formation of the large scale structure in the
universe in that it
a.
was clumpier than
normal matter in the early universe.
b.
consists exclusively of
antimatter particles.
c.
has a repulsive effect,
just like the dark energy.
d.
explains the physics of
black holes.
e.
cannot be made of
elementary particles.
35.
The best hypothesis
about the nature of dark matter is that it consists of particles with no electric charge. Why would such particles have no electric
charge?
a.
They cannot be more
massive than an electron.
b.
If they did, they would
emit photons as they move in external magnetic fields.
c.
Charged particles would
have been all annihilated in particle-antiparticle collisions in the early
universe.
d.
No elementary particle
has electric charge.
e.
Charged particles
formed only later inside stars.
36.
How do the properties
of the CMB give support to the existence of dark matter?
a.
The CMB has the same
temperature as the cold dark matter.
b.
The faint glow of the
CMB was actually produced by dark matter particles as they annihilated normal
matter particles.
c.
The opaque CMB is
essentially hiding the dark matter that existed earlier in the universe.
d.
The CMB is too smooth
to account for the structure we observe in the universe.
e.
The observed spatial
scale of CMB clumpiness perfectly matches that of the dark matter.
37.
In the early universe,
why were inhomogeneities in the distribution of normal matter much smaller than
inhomogeneities in the dark matter?
a.
Normal matter is pushed
away by supernova explosions.
b.
Magnetic fields
smoothed the distribution of charged particles in the normal matter but not in
dark matter.
c.
Dark matter particles
were more massive than and cooled off before normal matter, thus dark matter
fluctuations had a longer time over which to grow.
d.
Dark matter was 10
times more massive than normal matter.
e.
Radiation pressure
affected normal matter but not dark matter.
38.
The figure below shows
snapshots taken from the Bolshoi simulation of the formation of the large-scale
structure in the universe. Which one of these images represents the state of
the universe at the highest redshift?
a.
A
b.
B
c.
C
d.
D
e.
All of these occur at
the same redshift, just in different regions of the universe.
39.
Telescopes like ALMA
(working in the range 0.4-3 mm) and JWST (working in IR, in the range 0.6-28.5
micro-m) would help astronomers close a gap of observations that corresponds to
the window
a.
z = 2−3, when the star formation rate peaked.
b.
z = 10−1000, between the epochs of recombination and reionization.
c.
z = 0−0.5, when there was a big change in the relative fraction of
galaxies with peculiar morphologies.
d.
z > 1100, to directly observe the inflation epoch.
e.
such telescopes are
actually designed to only explore planetary systems within the boundaries of
our Milky Way.
40.
The future James Webb
telescope is designed to observe the most distant galaxies in the universe. It
will observe them in
a.
UV.
b.
IR.
c.
visible.
d.
X-ray.
e.
radio.
41.
The most distant
galaxies detected at z ≈ 10 are best observed with __________ wavelengths of light.
a.
infrared
b.
visible
c.
X-ray
d.
gamma ray
e.
radio
42.
At what redshift would
a quasar’s emission line emitted at 121.6 nm show up at the “normal” wavelength
of 486.1 nm of the Balmer Hฮฒ line?
a.
1
b.
2
c.
3
d.
5
e.
7
43.
What would be the
observed wavelength for the Balmer Hฮฒ line emitted at
486.1 nm by a quasar at redshift z = 5?
a.
2.9 ยตm
b.
81.0 nm
c.
21.0 cm
d.
121.6 nm
e.
1.2 ยตm
44.
Reionization of the
neutral gas in the universe occurred due to the
a.
decay of dark matter
particles.
b.
emission of neutrinos
by the first stars that formed.
c.
release of jets of
charged particles from supermassive black holes.
d.
radiation from the
first stars, supernovae, and black holes that formed.
e.
positron and electron
annihilations.
45.
The first stars formed
in the universe had ___________ compared with the stars formed today.
a.
higher heavy element
content and higher mass
b.
higher heavy element
content and lower mass
c.
lower heavy element
content and higher mass
d.
lower heavy element
content and lower mass
e.
higher mass and longer
lifetimes
46.
If astronomers discover
a new ultrafaint galaxy, where would it most likely to be found?
a.
on its own, away from
other galaxies
b.
a few billion light
years away from Earth
c.
at high redshift
d.
in a large galaxy
cluster
e.
orbiting the Milky Way
47.
Which of the following
does not describe the current view on the very first stars?
a.
They formed inside dark
matter minihalos.
b.
There was no dust
available to help the process of star formation.
c.
They must have been
tens of times more massive than our Sun.
d.
The material from which
they formed contained no elements more massive than lithium.
e.
The formed in large
clusters with numerous members.
48.
Which of the following
best explains the difference between the heavy-element abundances seen in the
first stars and those seen in stars that we observe today?
a.
Stars today have more
heavy elements, because modern stars have higher masses, allowing them to
create more heavy elements through nuclear fusion.
b.
Stars today have more
heavy elements, because the gas that formed the current stars was enriched by
the higher mass elements formed in previous generations of stars.
c.
Stars today have a
fewer heavy elements, because they have been around long enough to use up the
larger mass atoms.
d.
Stars today have a
smaller abundance of heavy elements, because they haven’t been around long
enough to make as many of the larger atoms.
e.
The stars that
astronomers observe now are the first generation of stars.
49.
Which of the following
is not true about ultrafaint dwarf galaxies?
a.
They may be the remains
of the first galaxies or first minihalos.
b.
They may offer support
for the bottom-up scenario.
c.
They have been
predicted but never been observed.
d.
They are dominated by
dark matter.
e.
They have fewer stars
than globular clusters do.
50.
The processes of galaxy
and star formation differ in all but one of the
following aspects. Which one?
a.
Star formation follows
a “top-down” sequence whereas galaxy formation involves a “bottom-up” sequence.
b.
Dark matter is
essential in the formation of galaxies, but it is not involved in the formation
of stars.
c.
Galaxy angular momentum
originates in interactions of clumps whereas star angular momentum is caused by
the turbulence of the original molecular clouds.
d.
The formation of a star
is a very slow process whereas a galaxy forms in a very short timescale due to
the huge difference in gravitational forces at play.
e.
When stars form, they
acquire most of the mass of the collapsing system whereas in a Milky Way−
like galaxy much of the matter remains distributed in a disk.
51.
of these is not
also true for galaxy formation?
a.
Angular momentum leads
to the formation of a disk.
b.
For both stars and
galaxies, the largest objects form first, with smaller objects coming together
later.
c.
A gas cloud radiates
energy, allowing it to collapse further than when it was hotter.
d.
Gravitational
instability leads to collapse.
e.
The original large gas
cloud splits into smaller fragments, because areas with higher density also
have greater gravitational pull.
52.
Which of these lists
shows the correct chronological order of the events listed, starting with the
earliest and ending with the most recent?
a.
reionization, dark
matter halos collapse, recombination, first galaxies are formed
b.
dark matter halos
collapse, reionization, first galaxies are formed, recombination
c.
reionization, first
galaxies are formed, dark matter halos collapse, reionization
d.
recombination, dark
matter halos collapse, first galaxies are formed, reionization
e.
first galaxies are formed,
dark matter halos collapse, reionization, recombination
53.
Low-mass stars could
form in the second generation because
a.
massive elements
produced in the first stars coalesced into dust grains.
b.
they formed in
minihalos of cold dark matter.
c.
gravitational waves led
to the fragmentation of dark matter minihalos into microhalos.
d.
there was a lot more
raw material available for star formation after the demise of the first stars.
e.
different types of
fundamental forces controlled the formation of the first and second generation.
54.
Choose the answer that
does not correctly describe the second generation of stars.
a.
They could have form
with low mass, because they formed in cooler environments.
b.
They contain small
amounts of many massive elements.
c.
A few of the low-mass
second-generation stars have been identified in the halo of the Milky Way.
d.
Their formation process
is very different fromm that of the first generation stars.
e.
The low-mass
second-generation stars are very hot and luminous and thus easy to detect.
55.
Panel (b) of the figure
below shows the enhanced infrared glow obtained after nearby stars and galaxies
are subtracted from a standard Spitzer Space Telescope exposure. Scientists
ascribe this faint signature to
a.
the CMB.
b.
the first stars and
galaxies formed.
c.
GRBs and quasars.
d.
supernovae.
e.
our Sun.
56.
What do astronomers
predict will be the final state of our universe?
a.
a Big Crunch in which
everything collapses back in on itself
b.
an ever-expanding
universe filled with nothing but hydrogen and helium gas
c.
a universe that stops
expanding and is filled with nothing but white dwarfs, neutron stars, and black
holes
d.
an ever-expanding
universe filled with photons and elementary particles
e.
a universe that stops
expanding once enough stars become black holes
57.
We expect the kinds of
galaxies that we see at redshift of z ≈ 4 to be
a.
much like what we see
today.
b.
smaller and much more
irregular looking than today.
c.
smaller versions of
what we see today.
d.
far more numerous but
with fewer spiral galaxies.
e.
larger versions of what
we see today.
58.
Compared with what we
see today, galaxies in the past were
a.
more ordered and more
likely to have spiral structure.
b.
more ordered and less
likely to have spiral structure.
c.
messier and more likely
to have spiral structure.
d.
messier and less likely
to have spiral structure.
e.
exactly the same as
they are today.
59.
Which of these
statements about galaxy clusters is true?
a.
Galaxy clusters do not
require dark matter in order to form.
b.
Galaxy clusters are the
largest structures in the universe.
c.
Small galaxy clusters
form first and then merge together to form larger galaxy clusters.
d.
Galaxy clusters are
evenly distributed throughout the universe.
e.
There are such large
distances between galaxy clusters that they never actually run into each other.
60.
Which probably formed
last in the course of the evolution of the universe?
a.
a typical proton inside
a water molecule on the Earth
b.
a helium atom in the
surface of the Sun
c.
a typical star that is
a member of a globular cluster star in our Milky Way
d.
the Milky Way
e.
the Virgo Supercluster
61.
Cosmologists estimate
that the last stars will form about ________ years from now.
a.
109
b.
1014
c.
1065
d.
1098
e.
10100
62.
Scientists estimate
that, in the distant cosmic future, before the universe becomes filled
exclusively with elementary particles, the last large concentrations of mass
will be
a.
white dwarfs.
b.
neutron stars.
c.
black holes.
d.
brown dwarfs.
e.
ultrafaint galaxies.
63.
If dark energy is
embedded within the vacuum of space, then the best places to study it would
probably be the
a.
spiral galaxies.
b.
interacting, peculiar
galaxies.
c.
cosmic walls and
filaments.
d.
cosmic voids.
e.
clusters of galaxies.
64.
The largest cosmic
supervoid ever discovered spans an estimated length of about 1.8 Gly. How many
Milky Way galaxies would fit side-to-side within this apparently empty region
in space?
a.
1.8
b.
18
c.
180
d.
18,000
e.
1.8 × 109
65.
Which of the following
is not likely to happen when two spiral galaxies collide?
a.
A more massive
elliptical galaxy might form out of the merger.
b.
The two supermassive
black holes at their centers could form a binary black hole system.
c.
Individual stars
collide to create many supernovae.
d.
A burst of star
formation will occur in the merged galaxy.
e.
The cold gas in the
merged galaxy might be blown away by supernovae.
66.
By measuring the star
formation rate in galaxies as a function of their redshift, we have learned
that the average star formation rate in galaxies peaked approximately _________
years ago.
a.
1 billion
b.
3 billion
c.
5 billion
d.
7 billion
e.
11 billion
67.
How has the fraction of
galaxies with peculiar morphologies evolved from z ≈ 0.4 to the present
epoch?
a.
About 10 percent of
today’s galaxies are peculiar, whereas at z ≈ 0.4 the fraction
increases to more than half.
b.
The fraction has been
the same 50 percent over the last 4−5 billion years.
c.
At the present epoch
there are far more interacting galaxies than when the universe was about 9−10 billion years
old.
d.
The fraction has been
unchanged 10 percent over the last 4−5 billion years.
e.
There are no peculiar
galaxies today, whereas at z ≈ 0.4 the fraction is close to 10 percent.
68.
Which of the following
may not necessarily be indicative of a “bottom-up” scenario for
galaxy formation?
a.
Galaxies observed at
very high redshift are typically 20 times smaller than the Milky Way.
b.
There are many more
peculiar galaxies at high redshift compared with those at low redshift.
c.
Our own galaxy, the
Milky Way, is classified as a barred spiral.
d.
Quasars exist even at
redshifts exceeding z = 7.
e.
The star formation rate
has changed over cosmological time.
69.
Ignoring the effect of
redshift, we expect the galaxies that we see at a redshift of z = 3 will be _____________ than galaxies today.
a.
more irregular and
redder
b.
larger and redder
c.
smaller and bluer
d.
smaller and redder
e.
larger and bluer
70.
Which of the following
is not a reason that supercomputer cosmological simulations like
Bolshoi are extremely valuable?
a.
They produce images
aesthetically suitable for the general public.
b.
Comparing simulations
to actual observational data sets constraints on fundamental parameters of the
universe.
c.
They can trace the
evolution of both visible and invisible matter in the universe.
d.
They can make
predictions that can be cross-checked against observations.
e.
They allow the study of
a sequential process of galaxy evolution.
71.
Which of the following
is not a consequence of intergalactic encounters and mergers?
a.
the rate of star
formation
b.
the activity of the
galactic supermassive black holes
c.
the formation of
supermassive black holes
d.
the changing
proportions of various morphological types with the age of the universe
e.
the cosmological
recession of galaxies
72.
The expansion of the
universe will eventually render the CMB invisible because its photons will
a.
have wavelengths that
will exceed than the size of the observable universe.
b.
be swamped by the light
from the ever-increasing star-formation rates in the universe.
c.
not have enough energy
to escape the gravity of degenerate stellar remnants.
d.
all combine and again
produce pairs of massive particles.
e.
not escape the strong
gravity of supermassive black holes the size of galaxy clusters.
73.
Which of these
statements about black holes in the early universe is not true?
a.
Supermassive black
holes affected the star formation rates in early galaxies.
b.
The growth of
supermassive black holes is likely linked with galaxy mergers.
c.
The first generation of
stars had high enough masses to leave black holes behind after exploding as
supernovae.
d.
The black holes in the
early universe should have been larger than those seen today.
e.
Supermassive black
holes may have formed from mergers of smaller black holes.
SHORT ANSWER
1.
Describe the large-scale
structure of the universe.
2.
In the context of the
galaxy clusters, rank the proportions of stellar, intergalactic (intra-cluster)
X-ray− emitting gas, and
dark matter mass.
3.
Studying galaxies of
various morphological types, scientists have estimated equivalent mass-to-light
ratios (M/L) of about 1−30 in solar units
(1 M⊙/ 1 L⊙), being lower for
spiral and higher for elliptical galaxies. In galaxy clusters, however, the
typical total mass-to-light ratio is estimated in the
range 300−600 (M⊙/L⊙). What is the
implication of these numbers?
4.
Explain what the arcs
seen in the Hubble Space Telescope image shown below represent.
5.
Scientists quantified
the following amounts of mass for the Coma cluster of galaxies: the total mass
of the cluster is Mtotal ~ 3.3 × 1015 M⊙, the total mass of all stars Mstars
~ 3 × 1013 M⊙, and the mass of the hot X-ray−emitting gas Mgas ~ 1 × 1014 M⊙. What is corresponding
percentage of dark matter within the Coma cluster?
6.
Use Hubble’s law to
explain how measurements of redshift help astronomers map out the large-scale
structure of the universe.
7.
Describe two ways in
which you could measure the mass of a galaxy cluster.
8.
How do we know how fast
the Milky Way is moving relative to the local universe? What are we moving
toward, and what do we think is mostly responsible for this motion?
9.
What is the fundamental
difference between the two types of dark matter candidates? List an example of
each type.
10.
Why do astronomers
think that cold dark matter (as opposed to hot dark matter) is the primary component
of dark matter in galaxies?
11.
How are the observed
properties of the CMB leading to the idea that dark matter plays a crucial role
in the formation of structure in the universe?
12.
Explain why the physics
of formation of the second generation stars is even more complex than that of
the first generation.
13.
Based on the figure and
chart shown below, roughly estimate the range of redshift defining (i.e.,
bracketing) the epoch of reionization.
14.
Explain why a galaxy
can collapse to a much smaller size than its dark matter halo.
15.
What are some other
possible candidates (macroscopic objects) for dark matter besides elementary
particles?
16.
What is the only
identified form of dark matter?
17.
What would be the
observed wavelength for the Lyman-alpha emission at 121.6 nm from the distant
galaxy at redshift z = 8.68?
18.
An astronomer wants to
study the epoch of reionization, which occurred roughly in the range of 6 < z < 11. What range of wavelength must the astronomer be able to
detect corresponding to light emitted at 500nm?
19.
In the immediate
aftermath of the recombination epoch, neutral hydrogen produced 21-cm photons.
What would be the corresponding observed wavelength (at the present epoch) for
such photons emitted at redshift z ~ 100?
20.
The Hubble Space
Telescope is equipped with an infrared camera WFC3/IR installed on it in 2009
during the last servicing mission, sensitive to photons up to about 1.7 ยตm. It is estimated
that the youngest (i.e., most distant) galaxy detected in the Hubble XDF
(eXtreme Deep Field; see the images in the figure shown below) existed just 450
million years after the Big Bang. What is the emitted wavelength from that
galaxy that was still detectable with the aforementioned infrared camera? (Note
that the redshift is z ~ 10.2 when the universe has the indicated very young age.)
21.
The Mid-Infrared
Instrument (MIRI) that will be attached to the James Webb Space Telescope
covers the wavelength range of 5 to 28 microns. Calculate over what redshift
range it can detect the 500 nm photons emitted by galaxies.
22.
What was temperature
and wavelength of the cosmic background blackbody signature at the epoch of
reionization, about 400 million years after Big Bang?
23.
Explain why dark matter
dominates the halos of galaxies but does not play a role in the formation of
small structures (stars, planets, etc.) within galaxies.
24.
What stage in the
evolution of the universe is coined as “the epoch of reionization,” and what is
the significance of this name?
25.
What was the cooling
mechanism that allowed the first stars to form?
26.
Explain and contrast
the top-down vs. bottom-up scenarios for star, galaxy, and galaxy cluster
formation, respectively.
27.
One of the most distant
galaxies observed to date shows a redshift z = 8.68, whereas one
of the most distant candidates (not fully confirmed yet) is a galaxy at a
redshift of about z ~ 10.7. Why are such discoveries, rare for now, so exciting?
28.
Outline a few
fundamental differences between the formation of the very first stars and that
of the second or subsequent generations.
29.
How do astronomers explain
the formation of elliptical galaxies?
30.
Explain how computer
simulations of structure formation and observations of the structure in the
universe today can help astronomers determine the nature of dark matter.
31.
Based on the snapshot
of a Bolshoi cosmological simulation in the figure below, roughly estimate the
size of the largest void captured in the frame. Note that each side of the
square field in the simulation represents 89 Mpc.
32.
Explain why the Bullet
Cluster is considered a strong example for the existence of dark matter, based
on the figure below.
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