Question 1

When does gravitational lensing occur?

Accepted Answer

Gravitational lensing occurs when light passes near a massive object and is deflected by the object's gravitational field. This can cause the light to bend and be distorted, creating a magnified or multiple image of the original source. The amount of lensing depends on the mass of the intervening object and the distance between the object and the observer.

Question 2

Which of the following types of objects is the Milky Way part of?

Accepted Answer

The Milky Way is part of a poor cluster of galaxies known as the Local Group, which contains fewer than 50 galaxies. It is not part of a rich or globular cluster, and while the Virgo Cluster is nearby, it is not a part of it.

Question 3

What does the term "galactic cannibalism" refer to?

Accepted Answer

Galactic cannibalism refers to the merging of galaxies, where one galaxy absorbs another.

Question 4

Which of the following best describes poor clusters?

Accepted Answer

Poor clusters contain fewer than 1000 galaxies and have irregular shapes. They tend to have a mix of spiral and elliptical galaxies and are found more often at the outskirts of galaxy clusters.

Question 5

What type of galaxy has an elongated nucleus with a spiral structure extending from the ends of the elongations?

Accepted Answer

This description matches the characteristics of a barred spiral galaxy, which has a central elongated bar structure with spiral arms extending out from the ends of the bar.

Question 6

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

Accepted Answer

Tidal tails are produced when two galaxies pass near each other and pull large streamers of stars, gas, and dust away from each other. Ring galaxies are formed when a smaller galaxy passes through the center of a larger galaxy, leaving a ring of stars. Rotation curves are graphs that show the velocity of stars and gas in a galaxy as a function of their distance from the center. Irregular galaxies are galaxies that do not fit into any other classification scheme and have no particular shape or structure.

Question 7

What is look-back time?

Accepted Answer

Look-back time is defined as the amount of time it takes for light from a distant object to reach Earth, which means it is directly related to the distance of the object from Earth. The farther an object is, the longer the look-back time is. Therefore, option A is the correct answer, and all other options are incorrect.

Question 8

What does an irregular galaxy contain?

Accepted Answer

Irregular galaxies are characterized by their lack of symmetry and structure. They contain both upper and lower main-sequence stars as well as gas and dust.

Question 9

What evidence leads astronomers to conclude that galaxies' shapes may be affected by the environment in which they are located?

Accepted Answer

The different fractions of galaxy types in rich clusters and poor clusters suggest that environmental factors play a role in shaping galaxy morphology. Rich clusters are denser and may have more interactions between galaxies, leading to a higher fraction of elliptical galaxies, while poor clusters have lower densities and may have more isolated galaxies, leading to a higher fraction of spiral galaxies. The other options (A, B, and C) do not directly suggest a link between environment and galaxy shapes.

Question 10

Mathematical models indicate that one type of galaxy is produced by high speed collisions in which a smaller galaxy passes through a larger galaxy almost perpendicular to the disk of the larger galaxy.What is this type of galaxy called?

Accepted Answer

A ring galaxy is formed when a smaller galaxy passes through a larger galaxy, often perpendicular to the disk, creating a ring-like structure.

Question 11

If you wanted to measure the distance to a galaxy,what kind of objects within it could you observe?

Accepted Answer

Cepheid variable stars have a well-defined relationship between their period of variability and their luminosity, making them useful for determining distances to galaxies. The other choices (A, B, and D) are not as useful for distance measurements.

Question 12

If a disk galaxy is reasonably close and edge-on,the Doppler shift of the galaxy disk material relative to the centre can be measured at several distances from the galaxy's centre.What does this measurement tell us about the galaxy?

Accepted Answer

The Doppler shift measurement of the galaxy disk material tells us about the galaxy's mass since this measurement relates to the rotational speed of the galaxy. The faster the rotational speed, the more massive the galaxy. This is known as the Tully-Fisher relation. The other choices are not directly related to the Doppler shift measurements.

Question 13

What does an elliptical galaxy contain?

Accepted Answer

Elliptical galaxies contain mostly lower main-sequence stars and giants. They have little gas and dust, and therefore, they are not active in star formation.

Question 14

Which of the following generally contain well over 1000 galaxies (mainly ellipticals)packed closely together?

Accepted Answer

Rich clusters are known to contain well over 1000 galaxies, mainly ellipticals, packed closely together. Local groups are small collections of a few dozen galaxies that include the Milky Way, whereas poor clusters contain fewer than 1000 galaxies. Tidal tails are elongated streams of stars, gas, and dust that are stretched out by gravitational interactions between galaxies.

Question 15

How might the mass of a single galaxy be found?

Accepted Answer

The rotation curve method involves observing the speeds of objects within a galaxy at different distances from the center. By analyzing this data, astronomers can determine the mass distribution of the galaxy, and hence estimate its total mass.

Question 16

What is a mega-parsec equivalent to?

Accepted Answer

A mega-parsec is equal to one million parsecs. One parsec is equal to 3.26 light years, so one mega-parsec is equal to 3.26 million light years. Therefore, the best choice is D.

Question 17

What information about a cluster of galaxies can lensing of background galaxies by the cluster be used to determine?

Accepted Answer

Lensing of background galaxies by a cluster of galaxies can be used to determine the mass of the cluster through the bending of light by the gravitational pull of the cluster. The other options, luminosity, distance, and diameter, cannot be directly determined through gravitational lensing.

Question 18

What does a spiral (S or SB)galaxy contain?

Accepted Answer

Spiral (S or SB) galaxies contain both upper and lower main-sequence stars, as well as gas and dust. This combination allows for ongoing star formation and the potential for the development of new planetary systems.

Question 19

Where is most of the mass of a galaxy found?

Accepted Answer

Most of the mass in a galaxy is in the form of dark matter, which does not emit or interact with light and is usually located in the halo surrounding the visible portion of the galaxy.

Question 20

The Hubble Law describes a relationship between two characteristics of a galaxy.What are they?

Accepted Answer

The Hubble Law describes a relationship between a galaxy's distance and its recession velocity (the speed at which it is moving away from us due to the expansion of the universe).

Quiz 10: Galaxies