Deck 23: Large-Scale Structure in the Universe

Question 1

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

Answer 1

a sponge with many large holes

Question 2

The Virgo Cluster is at an estimated distance of 16.5 Mpc.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) 3,800 km/s

Answer 2

1,200 km/s

Question 3

Which of the following is true about the Great Attractor?

A) It is about 5 Mpc away.
B) It is in fact a black hole the size of a galaxy.
C) It can only be detected in radio wavelengths.
D) It is at the center of the Laniakea Supercluster.
E) It has no gravitational effects.

Answer 3

It is at the center of the Laniakea Supercluster.

Question 4

Astronomers estimate distances to large numbers of distant galaxies using

A) the cosmological constant.
B) Cepheid variable stars.
C) parallax.
D) Type II supernovae.
E) redshifts.

Question 5

The diameter of the Local Group of galaxies is closest to which of the following distances?

A) 50 AU
B) 100,000 light-years
C) 3 million parsecs
D) 200 million light-years
E) 1 billion parsecs

Question 6

Which of the following fills the space between galaxies in a cluster?

A) young blue stars
B) old red stars
C) hot gas that glows at X-ray wavelengths
D) cold, dark gas that only glows in radio wavelengths
E) supermassive black holes

Question 7

Our galaxy is part of the ________ Supercluster.

A) Laniakea
B) Solar
C) Milky Way
D) Great Attractor
E) Andromeda

Question 8

Which of the following is a way in which astronomers detect dark matter in clusters of galaxies?

A) by determining the amount of mass necessary to gravitationally lens images of distant objects
B) by directly measuring the dark matter using infrared light
C) by measuring the peculiar velocity of the galaxy cluster
D) by determining the amount of mass necessary to gravitationally collapse clouds of gas to form the number of stars present
E) None of these; dark matter cannot be detected in any way.

Question 9

Astronomers can estimate distances to the galaxies in the figure below because of

A) the expansion of the universe.
B) our location at the center of the universe.
C) dark matter.
D) peculiar velocities.
E) gravitational redshift.

Question 10

The figure below shows a small section of the Virgo Cluster.The indicated galaxy can be classified as

A) elliptical.
B) peculiar.
C) dwarf.
D) ultrafaint.
E) quasar.

Question 11

Scientists estimate the following quantities for the Coma Cluster: the total mass of the cluster is M_total ~ 1.3 *10¹⁵ M_SUN, the total mass of all stars is M_stars ~ 3 *10¹³ M_SUN, and the mass of the hot X-ray-emitting gas is M_gas ~ 1 * 10¹⁴ M_SUN.What is the corresponding percentage of dark matter within the Coma Cluster?

A) 4 percent
B) 25 percent
C) 72 percent
D) 90 percent
E) There is no dark matter contribution.

Question 12

Which of the following provides 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) all of these

Question 13

A galaxy has a peculiar velocity due to the effects of

A) erroneous redshifts.
B) local gravitational attraction.
C) supernovae.
D) eclipsing binary stars.
E) interstellar winds.

Question 14

Filaments and voids are hallmarks of

A) reionization.
B) large-scale structure.
C) spiral galaxies.
D) elementary particles.
E) hot dark matter.

Question 15

Understanding the distribution of galaxies in the universe requires the construction of a three-dimensional map where for each galaxy we need to know its position and

A) mass.
B) redshift.
C) dust content.
D) morphological type.
E) star formation rate.

Question 16

Which of these is the correct order of collections of galaxies, from smallest to largest?

A) group, supercluster, cluster
B) cluster, supercluster, group
C) group, cluster, supercluster
D) cluster, group, supercluster
E) supercluster, group, cluster

Question 17

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

Question 18

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.

Question 19

Dark matter constitutes ________ of the mass in galaxy clusters, while the majority of non-dark matter mass is found in ________.

A) the majority; supermassive black holes
B) a minority; supermassive black holes
C) a minority; cold gas
D) the majority; hot gas
E) none; old stars

Question 20

In order to use Hubble's law to find the distance to a galaxy, astronomers need to measure that galaxy's

A) radius.
B) rotational velocity.
C) mass.
D) peculiar velocity.
E) redshift.

Question 21

Structure in our universe evolved by initially forming

A) giant galaxies, some of which later fragmented into dwarf galaxies.
B) dwarf galaxies that later merged to form bigger galaxies.
C) individual, free-floating stars, that later aggregated to form galaxies.
D) hot dark matter that later cooled into cold dark matter.
E) all types and sizes of galaxies at the same time.

Question 22

The expansion of the universe will eventually render the CMB invisible because its photons will

A) have wavelengths that will exceed 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.

Question 23

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.

Question 24

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.

Question 25

In the early universe, why were inhomogeneities in the distribution of normal matter much smaller than inhomogeneities in the dark matter?

A) Normal matter was pushed away by supernova explosions.
B) Large-scale 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, and so dark matter fluctuations had more time to grow.
D) Dark matter was 10 times more massive than normal matter.
E) Radiation pressure affected normal matter but not dark matter.

Question 26

What has the dominant role in defining the large-scale structure of the universe?

A) supernovae from the first generation of stars
B) the gravitational attraction of matter
C) matter/antimatter annihilation
D) magnetic fields
E) electric force

Question 27

The best hypothesis about the nature of dark matter is that it consists of particles with no electric charge.What is one reason why dark matter particles must have zero 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) All charged particles would have been annihilated in particle-antiparticle collisions in the early universe.
D) No elementary particle has electric charge.
E) Charged particles formed only later inside stars.

Question 28

Which of the following is true about neutrinos?

A) They are a possible example of cold dark matter.
B) They are a possible 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.

Question 29

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

Question 30

Our current understanding of galaxy formation suggests 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 over distances larger than those of dark matter halos.

Question 31

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.

Question 32

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 particles of normal matter.
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 unless dark matter exists.
E) The observed spatial scale of CMB clumping perfectly matches that of the dark matter.

Question 33

You observe two galaxy clusters, cluster A and cluster B.If the outer galaxies of both clusters have the same circular velocities, but cluster A has twice the mass of cluster B, then the size of cluster A must be

A) 4 times that of cluster B.
B) one-fourth that of cluster B.
C) twice that of cluster B.
D) half that of cluster B.
E) the same as cluster B.

Question 34

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.

Question 35

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.

Question 36

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.

Question 37

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.

Question 38

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.

Question 39

You observe two galaxy clusters, cluster A and cluster B.Both have the same radius, but cluster B's outer galaxies are orbiting the cluster with circular velocities that are twice that of cluster A's circular velocities.The mass of cluster B is

A) 2 times cluster A's mass
B) 4 times cluster A's mass.
C) half of cluster A's mass.
D) one-quarter of cluster A's mass.
E) equal to cluster A's mass.

Question 40

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) heating from the motion of high-velocity black holes.
D) radiation from the first stars, supernovae, and black holes that formed.
E) positron and electron annihilations.

Question 41

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

Question 42

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 fewer heavy elements because they have been around long enough to use up the larger 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.

Question 43

The second generation of stars

A) is indistinguishable from the first generation.
B) have all left the main sequence.
C) can only be found in galactic disks.
D) are all giant stars.
E) contain some elements heavier than lithium.

Question 44

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 H $\alpha$ line?

A) 1
B) 2
C) 3
D) 5
E) 7

Question 45

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

Question 46

Which of the following is true about ultrafaint dwarf galaxies?

A) They are surrounded by dark dust and gas.
B) They are sites of active star formation.
C) They are dominated by dark matter.
D) They have been predicted but have never been observed.
E) They are more massive than most dwarf galaxies.

Question 47

Which of the following statements about galaxy and star formation is true?

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 gravitational interactions of clumps whereas star angular momentum is caused by the turbulence of the original molecular clouds.
D) 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.
E) All of these statements are true.

Question 48

Telescopes like ALMA (working in the range 0.4-3.0 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 = 10-1,000, between the epochs of recombination and reionization.
C) z = 0-0.5, when there was a big change in the relative fraction of irregular galaxies.
D) z $\gt$ 1,100, to directly observe the inflation epoch.
E) Such telescopes are actually designed to only explore planetary systems within the boundaries of our Milky Way.

Question 49

The James Webb Space Telescope is designed to observe the most distant galaxies in the universe.It will observe them in

A) UV wavelengths.
B) IR wavelengths.
C) visible wavelengths.
D) X-ray wavelengths.
E) radio wavelengths.

Question 50

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.

Question 51

Each of these statements describes the steps that occur during star formation.Which 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.

Question 52

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.

Question 53

How has the fraction of galaxies with irregular morphologies evolved from 4 billion years ago to the present epoch?

A) About 10 percent of today's galaxies are peculiar, whereas 4 billion years ago more than half the galaxies were peculiar.
B) The fraction has remained at 50 percent over the last 4 billion to 5 billion years.
C) At the present epoch there are far more interacting galaxies than when the universe was about 9 billion to 10 billion years old.
D) The fraction has remained at 10 percent over the last 4 billion to 5 billion years.
E) There are no peculiar galaxies today, whereas 4 billion years ago they comprised nearly 10 percent of galaxies.

Question 54

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.

Question 55

What would be the observed wavelength for the Balmer H $\alpha$ line emitted at 486.1 nm by a quasar at redshift z =5?

A) 2.9 µm
B) 81.0 nm
C) 21.0 cm
D) 121.6 nm
E) 1.2 µm

Question 56

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, recombination
D) recombination, dark matter halos collapse, first galaxies are formed, reionization
E) first galaxies are formed, dark matter halos collapse, reionization, recombination

Question 57

Where would a newly-discovered ultrafaint galaxy most likely be found?

A) on its own, away from other galaxies
B) a few billion light-years from Earth
C) at high redshift
D) in a large galaxy cluster
E) orbiting the Milky Way

Question 58

Which of the following must be true about the very first stars?

A) They couldn't form until billions of years after the Big Bang.
B) They were made of dark matter.
C) They all had low (less than 1 M_SUN) masses.
D) They formed in large clusters of millions of stars, which became galaxies.
E) The material from which they formed contained no elements more massive than lithium.

Question 59

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.

Question 60

Spiral galaxies

A) were present during the Big Bang.
B) formed immediately after recombination.
C) formed at the same time as the first stars.
D) took some time to form, after the first stars appeared.
E) can have existed only for the last billion years or so.

Question 61

Describe two ways in which you could measure the mass of a galaxy cluster.

Question 62

What is the expected future of our galaxy?

A) Its contents will eventually be pulled in by the supermassive black hole at its center, Sagittarius A*.
B) Eventually all its matter will be in the form of iron atoms.
C) It will eventually be made of nothing but white dwarfs, neutron stars, and black holes, and then will collapse in on itself in a Big Crunch.
D) It will merge with nearby galaxies and then eventually decay into photons.
E) It will expand with the universe, but will stop expanding once enough stars become black holes.

Question 63

Out of all the mass and energy in the universe, ordinary matter (the stuff that makes up stars and gas, and all the things we interact with in everyday life) constitutes about

A) 4-5 percent.
B) 10 percent.
C) half.
D) 85 percent.
E) 99 percent.

Question 64

Describe the large-scale structure of the universe.

Question 65

Which probably formed last in the course of the evolution of the universe?

A) a typical proton inside a water molecule on 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

Question 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

Question 67

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 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.

Question 68

According to the figure below, the maximum star formation rate in the past was about ________ the star formation rate today.

A) the same as
B) 5 times
C) 20 times
D) 100 times
E) 10,000 times

Question 69

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, irregular galaxies.
C) cosmic walls and filaments.
D) cosmic voids.
E) clusters of galaxies.

Question 70

A galaxy cluster is measured to have a radius of 8 x10¹⁹ km, and the small outer galaxies are measured to orbit the cluster center with a circular velocity of 900 km/s.What is the mass of this cluster's core? (Recall that G = 6.67 *10^-11 N m² kg^-2.)

Question 71

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.

Question 72

Which of the following is 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) A burst of star formation will occur in the merged galaxy.
D) The cold gas in the merged galaxy might be blown away by supernovae.
E) All of these are likely.

Question 73

What role do cosmological computer simulations play in the scientific method?

A) They create virtual observations, allowing scientists to test hypotheses without gathering data.
B) They design experiments.
C) They create predictions that can be tested with additional observations.
D) Simulations do not tie into the scientific method; they are only used to verify the math within theories.
E) Simulations do not tie into the scientific method; they only provide scientists tools to visualize concepts.

Question 74

In 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_SUN/1 L_SUN), with ratios being lower for spiral galaxies and higher for elliptical galaxies.In galaxy clusters, however, the typical total mass-to-light ratio is estimated in the range 300-600 (M_SUN/L_SUN).What is the implication of these numbers?

Question 75

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

Question 76

Use Hubble's law to explain how measurements of redshift help astronomers map the large-scale structure of the universe.

Question 77

What do the arcs seen in the Hubble Space Telescope image below represent?

Question 78

Explain why the Bullet Cluster is considered a strong example for the existence of dark matter, based on the figure below.

Question 79

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?

Question 80

Scientists quantified the following amounts of mass for the Coma Cluster: the total mass of the cluster is M_total ~ 1.3 * 10¹⁵ M_SUN, the total mass of all stars M_stars ~ 3 * 10¹³ M_SUN, and the mass of the hot X-ray-emitting gas M_gas ~ 1 * 10¹⁴ M_SUN.What is the corresponding percentage of dark matter within the Coma Cluster?