Question 1

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.

Accepted Answer

The current understanding of cosmic structure formation suggests that small structures like dwarf galaxies formed first and then merged over time to create larger galaxies. This is consistent with the hierarchical model of galaxy formation.

Question 2

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.

Accepted Answer

As the universe expands, the wavelengths of the CMB photons will continue to stretch, eventually becoming so long that they will exceed the size of the observable universe, making them effectively invisible.

Question 3

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.

Accepted Answer

Quantum fluctuations in the early universe are believed to have been the initial irregularities that, through gravitational attraction, led to the formation of large-scale structures like galaxies.

Question 4

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.

Accepted Answer

Dark matter was clumpier than normal matter in the early universe, which helped in the formation of galaxies and large-scale structures by providing gravitational wells for normal matter to fall into.

Question 5

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.

Accepted Answer

Radiation pressure from photons in the early universe smoothed out fluctuations in normal matter, which interacts with radiation, while dark matter does not interact with radiation and thus retained its inhomogeneities.

Question 6

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

Accepted Answer

The gravitational attraction of matter is the dominant force shaping the large-scale structure of the universe, as it governs the formation and evolution of galaxies, clusters, and larger cosmic structures.

Question 7

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.

Accepted Answer

If dark matter particles had electric charge, they would interact with electromagnetic fields and emit photons, which is not observed.

Question 8

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.

Accepted Answer

Neutrinos are considered a possible example of hot dark matter because they are light and move at relativistic speeds. They have been detected and do not account for all dark matter.

Question 9

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

Accepted Answer

Dark energy and cold dark matter are the two main components of the Lambda-CDM model, which is the most widely accepted cosmological model. Dark energy is a hypothetical form of energy that is believed to be responsible for the observed acceleration of the expansion of the universe, while cold dark matter is a hypothetical form of matter that is believed to make up most of the matter in the universe.

Question 10

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.

Accepted Answer

The visible parts of galaxies form in the densest regions of dark matter halos, where gas can cool and condense to form stars.

Question 11

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.

Accepted Answer

The answer of The figure below shows snapshots taken from...

Question 12

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.

Accepted Answer

The CMB's smoothness and uniformity suggest that normal matter alone couldn't have formed the large-scale structures we see today without the gravitational influence of dark matter.

Question 13

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.

Accepted Answer

The circular velocity of galaxies in a cluster is determined by the balance between gravitational force and centripetal force. If cluster A has twice the mass of cluster B but the same circular velocity, then the radius of cluster A must be twice that of cluster B to maintain this balance.

Question 14

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.

Accepted Answer

Quantum fluctuations during the inflationary period of the early universe are believed to have been stretched to macroscopic scales, leading to the small density variations that eventually grew into the large-scale structures we observe in the universe today.

Question 15

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.

Accepted Answer

The answer of The figure below shows snapshots taken from...

Question 16

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.

Accepted Answer

Neutrinos are considered hot dark matter because they move at relativistic speeds. This means they cannot clump together to form smaller structures like galaxies, which is inconsistent with observations of the universe's structure.

Question 17

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.

Accepted Answer

In hierarchical structure formation, small objects like galaxies and star clusters form first and then merge over time to create larger structures such as galaxy clusters and superclusters.

Question 18

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.

Accepted Answer

Dark matter does not interact electromagnetically, so it cannot lose energy through radiation and thus cannot collapse to form dense structures like the visible parts of galaxies.

Question 19

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.

Accepted Answer

The mass of a galaxy cluster can be determined using the formula for circular velocity: $v^2 = \frac{GM}{r}$. Since the velocities are squared, if cluster B's velocities are twice that of cluster A, then the mass of cluster B must be four times that of cluster A to maintain the same radius.

Question 20

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.

Accepted Answer

Reionization occurred due to the radiation from the first stars, supernovae, and black holes, which emitted high-energy photons capable of ionizing the neutral hydrogen in the universe.

Quiz 23: Large-Scale Structure in the Universe

Structure in our universe evolved by initially forming

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

Quantum fluctuations in the early universe

Dark matter is essential in understanding the formation of the large-scale structure in the universe in that it

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

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

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?

Which of the following is true about neutrinos?

The Lambda-CDM model combines the properties of ________ to explain the formation of structure in the universe.

Our current understanding of galaxy formation suggests that the visible parts of galaxies

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?

How do the properties of the CMB give support to the existence of dark matter?

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

The small density variations that subsequently led to the formation of large-scale structure in the universe are thought to have formed

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?

Scientists think that neutrinos cannot be the dominant form of dark matter in the universe.Why?

Structure formation in the universe proceeds hierarchically, meaning that

Why can't dark matter halos collapse to be the same size as the visible parts of galaxies?

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

Reionization of the neutral gas in the universe occurred due to the