Question 1

The rotation curve of a galaxy can be used to determine

Accepted Answer

The rotation curve of a galaxy can be used to determine the mass of the galaxy, as the rotation of the galaxy is dependent on the amount of mass within it. The other choices, such as the number of young stars and the amount of gas and dust, may be related to the mass of the galaxy, but they are not directly determined by the rotation curve.

Question 2

We should expect galaxies to collide fairly often because

Accepted Answer

Galaxies are large with respect to their separation distances and they occur in clusters. Both of these factors increase the probability of galaxies colliding with one another. Galaxies have significant gravity that can affect other galaxies nearby, increasing the likelihood of collisions. The high density of galaxies in clusters also makes collisions more likely. Hence, we should expect galaxies to collide fairly often.

Question 3

Gravitational lensing

Accepted Answer

Gravitational lensing occurs when light passes near a massive object and is deflected by the object's gravitational field. This phenomenon can be used to study the distribution of dark matter in the universe and to detect and study distant objects such as galaxies and quasars.

Question 4

__________ can be used to determine the galaxy's mass if the galaxy is reasonably close, so that the Doppler shift of the galaxy disk material can be measured at several distances from the galaxy's center relative to the center.

Accepted Answer

A galaxy's rotation curve can be used to determine the galaxy's mass if the galaxy is reasonably close, so that the Doppler shift of the galaxy disk material can be measured at several distances from the galaxy's center relative to the center. By plotting the rotation speed against the distance from the center, the mass of the galaxy can be inferred from the amount of gravitational pull needed to maintain the observed rotation curve.

Question 5

___________ have elongated nuclei with spiral structure extending from the ends of the elongations. The Milky Way is a member of this class of galaxy.

Accepted Answer

Barred spiral galaxies have elongated nuclei with a bar-like structure, and the Milky Way is classified as a barred spiral galaxy.

Question 6

The look-back time is

Accepted Answer

The look-back time is defined as the time it takes for light from an object to reach Earth. It is also numerically equal to the distance in light-years. Therefore, E is the correct answer. The statement that it is smaller for more distant objects is incorrect as the look-back time increases with the distance of the object. Hence, D is incorrect.

Question 7

Mathematical models indicate that ___________ galaxies are produced by high-speed collisions in which a smaller galaxy passes through another galaxy almost perpendicular to the disk of the galaxy.

Accepted Answer

Ring galaxies are formed as a result of high-speed collisions where a smaller galaxy passes almost perpendicular through the disk of a larger galaxy, creating a ring-like structure.

Question 8

The total mass of galaxies in a cluster of galaxies divided by the number of galaxies in the cluster can be used to determine a typical galaxy's ___________.

Accepted Answer

Dividing the total mass of galaxies in a cluster by the number of galaxies gives the average mass of each galaxy in the cluster, which can be used to determine a typical galaxy's mass.

Question 9

Poor clusters

Accepted Answer

Poor clusters contain fewer than 1000 galaxies and are characterized by their irregular shapes, distinguishing them from rich clusters which are more densely populated and have a more defined structure.

Question 10

A ___________ generally contains well over 1000 galaxies and is quite dense. They often contain many giant elliptical galaxies.

Accepted Answer

Rich clusters are known to contain well over 1000 galaxies and are quite dense compared to poor clusters. They are the largest known gravitationally bound structures in the universe and often contain many giant elliptical galaxies.

Question 11

Most of the mass of a galaxy is contained in the

Accepted Answer

Dark matter makes up about 85% of the total matter in a galaxy and is responsible for most of the gravitational force that holds the galaxy together. The other options listed contain only a small fraction of the total mass of a galaxy.

Question 12

The mass of a single galaxy might be found by

Accepted Answer

The rotation curve method is the best choice for finding the mass of a single galaxy. This method involves measuring the velocities of stars or gas clouds in the galaxy as a function of their distance from the galactic center. From this data, the mass of the galaxy can be estimated using the laws of gravity and motion. The other methods listed (double galaxy and cluster method) are better suited for measuring the mass of groups of galaxies rather than individual ones.

Question 13

___________ galaxies contain large clouds of gas and dust, both young and old stars, but have no obvious spiral arms or nucleus.

Accepted Answer

Irregular galaxies, as the name suggests, do not have a distinct shape or structure. They are often characterized by large clouds of gas and dust, as well as young and old stars. They do not have a well-defined nucleus or spiral arms, making them the best choice for this question. Option B) S0 is a lenticular galaxy with a disk-like structure but no spiral arms, while options C) E7 and E) E0 are elliptical galaxies with no gas, dust or recent star formation. Option D) Sa is a type of spiral galaxy with a well-defined nucleus and tightly-wound spiral arms.

Question 14

The Hubble law is a relation between a galaxy's

Accepted Answer

The Hubble law describes the relationship between a galaxy's distance and its recession velocity, stating that the farther away a galaxy is, the faster it appears to be moving away from us. This is the basis for the expansion of the universe. The other choices, such as mass and luminosity, are not directly related to the Hubble law.

Question 15

___________ are produced when two galaxies pass near each other and pull large streamers of stars, gas, and dust away from the galaxies.

Accepted Answer

Tidal tails are produced as a result of tidal forces when two galaxies pass near each other. These forces pull large streamers of stars, gas, and dust away from the galaxies, creating long, extended tails that can stretch into space for thousands of light years. Tidal tails are a common feature of galaxy interactions and can provide insight into the dynamics of these events.

Question 16

The Milky Way is part of 
I.a poor cluster.
II.a rich cluster.
III.the Virgo Cluster.
IV.the Local Group.

Accepted Answer

The Milky Way is not part of a rich cluster like choice II and it is not part of the Virgo Cluster as a whole but rather part of the Local Group, which includes the Andromeda Galaxy and smaller galaxies. Therefore, choices I and III are incorrect. The correct choices are I and IV, as the Milky Way is part of a poor cluster called the Local Group.

Question 17

A mega-parsec (Mpc) is equivalent to

Accepted Answer

A mega-parsec (Mpc) is equivalent to approximately 3.26 million light-years, making option D correct.

Question 18

A megaparsec is equivalent to

Accepted Answer

A megaparsec is a unit of distance in astronomy that is equal to one million parsecs. A parsec is approximately 3.26 light-years, so a megaparsec represents a much larger distance than the other options suggest.

Question 19

Galactic cannibalism refers to

Accepted Answer

Galactic cannibalism refers to the merging of galaxies, where one galaxy absorbs another galaxy or a smaller satellite galaxy. This process is also known as galactic merger or accretion. As the galaxies merge, their central black holes also combine, leading to the formation of a single, more massive black hole at the center of the resulting galaxy. Galactic cannibalism is believed to be a common phenomenon in the universe, and it plays a significant role in galaxy evolution.

Question 20

Astronomers now speculate that a galaxy's shape depends on all of the following except

Accepted Answer

All of the other choices may be important in determining a galaxy's shape. The rate of star formation affects the distribution of gas and dust within the galaxy, which may impact its shape. The history of past collisions can also alter a galaxy's shape, depending on the direction and angle of the collisions. The mass of a galaxy can affect the gravitational forces that shape and hold it together. Therefore, all of these factors are important in determining a galaxy's shape.

Quiz 13: Galaxies: Normal and Active