Question 1

Imagine that Hubble discovered that the recession velocity of a galaxy increased proportionally to the square of the galaxy's distance from the Milky Way.Which of the following would NOT be true?
A) Astronomers could calculate a galaxy's distance from its redshift.
B) The density of the Universe would decrease with time.
C) Astronomers would observe more distance galaxies as they were farther back in time.
D) Astronomers in any other galaxy would measure the same relationship.

Accepted Answer

The correct relationship discovered by Hubble is that the recession velocity of a galaxy increases linearly with its distance from the Milky Way (or any other observation point), not proportionally to the square of the distance. This linear relationship is fundamental to the cosmological principle, which states that the universe is homogeneous and isotropic on large scales, meaning it looks the same in all directions and from all points. If the recession velocity increased with the square of the distance, this would imply a different kind of expansion, not consistent with the observed isotropy and homogeneity of the universe. Thus, astronomers in other galaxies would not necessarily measure the same squared relationship, making option D incorrect based on the hypothetical scenario provided.

Question 2

Which of the following objects will produce the strongest gravitational lensing,all other things being equal?
A) the hottest galaxy cluster
B) the most distant galaxy cluster
C) the most massive galaxy cluster
D) the galaxy cluster with the largest radius

Accepted Answer

The most massive galaxy cluster will produce the strongest gravitational lensing because it has a greater amount of dark matter, which is the main contributor to creating the gravitational pull that causes lensing.

Question 3

A region 1 Mpc across contains a total mass of 10¹³ MSᵤn.What kind of object is this most likely to be?
A) a spiral galaxy
B) an elliptical galaxy
C) a galaxy group
D) a galaxy cluster

Accepted Answer

A region 1 Mpc across with a total mass of 10¹³ MSun is most likely a galaxy group. Galaxy groups are collections of galaxies that are smaller than galaxy clusters, typically containing a few to several dozen galaxies, and can have masses in the range of 10¹³ MSun. This size and mass do not typically correspond to individual galaxies (spiral or elliptical) or larger galaxy clusters, which can contain hundreds or thousands of galaxies and have much higher masses.

Question 4

Suppose Hubble's constant was equal to 300 km/s/Mpc.If you approximate 1 Mpc = 3 x 10¹⁹ km,and 1 year = 3 x 10⁷ s,how old would the Universe be?
A) 500 Myr
B) 3 Gyr
C) 13 Gyr
D) 50 Gyr

Accepted Answer

The age of the Universe is approximately the inverse of Hubble's constant. Converting Hubble's constant to s⁻¹ and taking the inverse gives an age of about 3 Gyr.

Question 5

Two galaxy clusters have identical radii,but the galaxies in cluster A have a typical orbital velocity of 700 km/s,while the galaxies in cluster B have a typical velocity of 1,400 km/s.How do the masses of these clusters compare to each other?
A) Cluster B is half as massive as cluster A.
B) Cluster B is twice as massive as cluster A.
C) Cluster B is four times as massive as cluster A.
D) Cluster B is eight times as massive as cluster A.

Accepted Answer

The orbital velocity of a galaxy within a cluster is related to the mass of the cluster through the equation v=√(GM/r), where v is the velocity, G is the gravitational constant, M is the mass of the cluster, and r is the radius of the cluster. If we assume that the two clusters have the same radius, we can set their orbital velocities equal to each other and solve for the ratio of their masses:

v_A = √(GM_A/r)
v_B = √(GM_B/r)
v_B/v_A = √(M_B/M_A)

We are given that v_B = 2v_A, so substituting for both velocities and solving for M_B/M_A, we get:

2 = √(M_B/M_A)
4 = M_B/M_A

Therefore, cluster B is four times as massive as cluster A.

Question 6

Imagine that an astronomer in an alternate universe observes all galaxies to be blueshifted relative to the Milky Way.Which of the following would this imply?
A) The Big Bang happened in the recent past.
B) Space is contracting.
C) The Milky Way is the center of the universe.
D) Galaxies do not rotate

Accepted Answer

In our universe, galaxies are observed to be redshifted, which indicates that the universe is expanding. If all galaxies were blueshifted in an alternate universe, it would suggest that space itself is contracting, bringing all the galaxies closer together.

Question 7

The high temperature and pressure of gas in the intracluster medium of galaxy clusters implies that:
A) clusters are in the midst of expanding.
B) clusters host powerful active galactic nuclei.
C) many of the cluster galaxies are obscured by absorption from the intracluster medium.
D) clusters are dominated by dark matter.

Accepted Answer

The high temperature and pressure of the gas in the intracluster medium suggest that galaxy clusters are dominated by dark matter. This is because the gravitational pull of a large amount of mass is required to heat and confine the intracluster gas, and dark matter is the most plausible source of this mass, given that it constitutes about 85% of the total matter in the universe.

Question 8

An astronomer observes three large spiral galaxies within a radius of 1 Mpc of each other.This is most likely a galaxy:
A) group.
B) cluster.
C) association.
D) merger.

Accepted Answer

Groups of galaxies are smaller collections typically containing a few to several dozen galaxies within a few million light-years of each other, fitting the description of the observation.

Question 9

Which physical law allows astronomers to probe the Universe's past?
A) gravitational lensing
B) the Doppler effect
C) the finite speed of light
D) the inverse square law

Accepted Answer

The finite speed of light allows astronomers to probe the Universe's past. This is because it takes time for light from distant objects to reach us, so we can see them as they were in the past. By looking at objects that are further away, we can observe events that happened billions of years ago.

Question 10

What is the most likely source of the hot gas halos (with temperatures of 10 million K)within galaxy clusters?
A) ram pressure stripping of molecular clouds within galaxies
B) the individual halos of the constituent galaxies
C) by-products of stellar fusion
D) gas expelled from a central active galactic nucleus

Accepted Answer

The answer of What is the most likely source of...

Question 11

If an astronomer looked at the field shown in the image below with an X-ray telescope,what would he or she see? 
A) small blobs of high-temperature emission around each of the large galaxies
B) a few bright point-like emitters
C) a large, high-temperature-emitting region spanning all the galaxies
D) no significant emission

Accepted Answer

The answer of If an astronomer looked at the field...

Question 12

Imagine that the expansion of the Universe proceeds at a constant rate at later times.How will the redshift of a particular galaxy change?
A) It will decrease.
B) It will remain the same, because the light will spend more time traveling.
C) It will remain the same, because all lengths expand by the same factor.
D) It will increase.

Accepted Answer

If the Universe is expanding at a constant rate, the distance between galaxies is constantly increasing, causing the wavelength of light emitted by a galaxy to stretch and the redshift to increase. Therefore, the answer is D, it will increase.

Question 13

What is the typical environment of a spiral galaxy?
A) isolated
B) inside a group of a few dozen members
C) inside a group with 100 members
D) inside a cluster with 1,000 or more members

Accepted Answer

Spiral galaxies are typically found inside groups that contain a few dozen members. These environments allow for the conditions necessary for spiral structures to form and persist.

Question 14

Which nearby object has at least 1,300 galaxies in a region about 5 Mpc across?
A) the Virgo Cluster
B) the Great Wall
C) the Local Group
D) the Taurus cluster

Accepted Answer

The Virgo Cluster is a nearby galaxy cluster that contains at least 1,300 galaxies in a region about 5 Mpc (16 million light-years) across. This makes it one of the closest and largest galaxy clusters to our own Milky Way galaxy. The Great Wall is a large-scale structure of galaxies that extends over a much larger distance of about 500 million light-years and is not localized to a region 5 Mpc across. The Local Group is a group of galaxies that includes the Milky Way and several nearby galaxies, but does not contain 1,300 galaxies within a region of 5 Mpc. The Taurus cluster is a relatively small and distant galaxy cluster that is not known to contain at least 1,300 galaxies within 5 Mpc.

Question 15

An astronomer observes many galaxies in distant parts of the sky to have emission lines redshifted relative to the same lines seen in a laboratory.What is the most likely explanation?
A) Space is expanding.
B) The galaxy is experiencing gravitational lensing.
C) The galaxy has a strong wind.
D) The galaxy is moving through space away from the Milky Way.

Accepted Answer

The redshift of emission lines is a common observation in astronomy and is explained as a result of the expansion of the universe. As the galaxies are moving away from us, the light they emit is stretched out, resulting in a redshift of the observed lines.

Question 16

Imagine that astronomers in an alternate universe discover that galaxies at all distances from the Milky Way have similar luminosities,stellar properties,and structures.Which of the following is most likely to follow in this universe?
A) The Big Bang did not occur.
B) Galaxies cannot form new stars.
C) There is very little obscuring dust between galaxies.
D) The universe is shaped like a sphere.

Accepted Answer

If galaxies at all distances have similar properties, it suggests a static universe without the expansion and evolution predicted by the Big Bang theory.

Question 17

Collisions are important in forming:
A) elliptical galaxies.
B) galaxy groups.
C) galaxy clusters.
D) barred spiral galaxies.

Accepted Answer

Collisions and mergers of smaller galaxies are a key process in the formation of elliptical galaxies.

Question 18

Which of the following astronomical objects has the largest look-back time?
A) a galaxy with z = 1
B) a supernova with z = 3
C) a quasar with z = 6
D) a gamma-ray burst with z = 8

Accepted Answer

Look-back time increases with redshift (z), and the gamma-ray burst with z = 8 has the highest redshift, indicating it is the most distant and thus has the largest look-back time.

Question 19

Which of the following discoveries disproved Aristotle's conception of an unchanging cosmos?
A) the existence of galaxies
B) the finite speed of light
C) Hubble's law
D) the cosmic microwave background

Accepted Answer

Hubble's law, which states that galaxies are moving away from us at speeds proportional to their distance, directly contradicted Aristotle's idea of an unchanging universe by demonstrating that the universe is expanding.

Question 20

Which of the following configurations is most likely to produce an Einstein ring?
A) a massive galaxy in the center of a spherical galaxy cluster
B) a massive galaxy in the center of a football-shaped galaxy cluster
C) a distant galaxy situated behind a football-shaped galaxy cluster
D) a distant galaxy situated behind a spherical galaxy cluster

Accepted Answer

A distant galaxy situated behind a spherical galaxy cluster is most likely to produce an Einstein ring as the gravitational lensing effect produced by the massive cluster will distort and magnify the light from the background galaxy in a circular pattern, creating an Einstein ring. In option A and B, the presence of a massive galaxy in the center of the cluster may cause gravitational lensing, but it would not necessarily produce an Einstein ring. Option C only mentions a football-shaped galaxy cluster which may cause gravitational lensing, but it does not guarantee the formation of an Einstein ring.

Quiz 17: The Cosmic Web: the Large-Scale Structure of the Universe

Imagine that Hubble discovered that the recession velocity of a galaxy increased proportionally to the square of the galaxy's distance from the Milky Way.Which of the following would NOT be true?

Which of the following objects will produce the strongest gravitational lensing,all other things being equal?

A region 1 Mpc across contains a total mass of 10¹³ MSᵤn.What kind of object is this most likely to be?

Suppose Hubble's constant was equal to 300 km/s/Mpc.If you approximate 1 Mpc = 3 x 10¹⁹ km,and 1 year = 3 x 10⁷ s,how old would the Universe be?

Two galaxy clusters have identical radii,but the galaxies in cluster A have a typical orbital velocity of 700 km/s,while the galaxies in cluster B have a typical velocity of 1,400 km/s.How do the masses of these clusters compare to each other?

Imagine that an astronomer in an alternate universe observes all galaxies to be blueshifted relative to the Milky Way.Which of the following would this imply?

The high temperature and pressure of gas in the intracluster medium of galaxy clusters implies that:

An astronomer observes three large spiral galaxies within a radius of 1 Mpc of each other.This is most likely a galaxy:

Which physical law allows astronomers to probe the Universe's past?

What is the most likely source of the hot gas halos (with temperatures of 10 million K) within galaxy clusters?

If an astronomer looked at the field shown in the image below with an X-ray telescope,what would he or she see?

Imagine that the expansion of the Universe proceeds at a constant rate at later times.How will the redshift of a particular galaxy change?

What is the typical environment of a spiral galaxy?

Which nearby object has at least 1,300 galaxies in a region about 5 Mpc across?

An astronomer observes many galaxies in distant parts of the sky to have emission lines redshifted relative to the same lines seen in a laboratory.What is the most likely explanation?

Imagine that astronomers in an alternate universe discover that galaxies at all distances from the Milky Way have similar luminosities,stellar properties,and structures.Which of the following is most likely to follow in this universe?

Collisions are important in forming:

Which of the following astronomical objects has the largest look-back time?

Which of the following discoveries disproved Aristotle's conception of an unchanging cosmos?

Which of the following configurations is most likely to produce an Einstein ring?