Question 1

Clusters of galaxies can be rich or poor, regular or irregular. But one thing they all have in common is that, if all galaxies could be detected, the majority of galaxies would be

Accepted Answer

Elliptical galaxies are the most common type found in galaxy clusters, especially in the dense centers of these clusters. This is because the conditions in clusters, such as high galaxy densities and frequent interactions, favor the formation and preservation of elliptical galaxies over other types.

Question 2

The Milky Way Galaxy is a(n)

Accepted Answer

The Milky Way Galaxy is part of the Local Group, which is considered a poor cluster of galaxies because it contains only a few dozen galaxies, as opposed to rich clusters that contain thousands.

Question 3

What is the galaxy content of rich, regular clusters like the Coma cluster?

Accepted Answer

Rich, regular clusters like the Coma cluster are characterized by a predominance of elliptical and S0 (lenticular) galaxies, with relatively few spiral and irregular galaxies. This is due to the dense environment of such clusters, which is conducive to the transformation of spiral galaxies into ellipticals and S0s through processes like galaxy mergers and interactions.

Question 4

Which of these bodies is NOT one of the satellite galaxies that surround the Milky Way Galaxy?

Accepted Answer

The Andromeda Galaxy is not a satellite galaxy of the Milky Way; it is a separate, large spiral galaxy that is actually on a collision course with the Milky Way, expected to merge with it in the distant future. The Small Magellanic Cloud, Large Magellanic Cloud, and Canis Major Dwarf elliptical galaxy are all satellite galaxies of the Milky Way.

Question 5

The estimated distance from Earth to the Coma cluster of galaxies is about

Accepted Answer

The Coma Cluster of galaxies is approximately 300 million light-years away from Earth. This distance places it well outside our own galaxy, the Milky Way, and makes it one of the relatively nearby clusters of galaxies in the observable universe.

Question 6

What is the famous Virgo cluster of galaxies?

Accepted Answer

The Virgo cluster is a rich, irregular cluster of over 1000 galaxies and is the closest large cluster of galaxies to the Local Group.

Question 7

The Local Group is

Accepted Answer

The Local Group is a collection of galaxies that includes the Milky Way. It is considered a "poor" cluster due to its relatively small number of galaxies compared to richer galaxy clusters.

Question 8

What is the galaxy content of rich, irregular clusters of galaxies such as the Hercules cluster?

Accepted Answer

Rich, irregular clusters of galaxies, like the Hercules cluster, tend to have a composition where spirals outnumber ellipticals, with more than one-half of the galaxies being spirals and less than one-quarter being ellipticals. This reflects the less densely packed and more dynamically young nature of these clusters compared to their rich, regular counterparts, which are more dominated by elliptical galaxies.

Question 9

The total number of galaxies in a rich, regular cluster of galaxies such as the Coma cluster is believed to be

Accepted Answer

Rich, regular clusters of galaxies, like the Coma Cluster, typically contain a few thousand to 10,000 galaxies. These clusters are massive collections of galaxies bound together by gravity, and their large numbers reflect the dense concentration of galaxies in these regions of space.

Question 10

The light that arrives at Earth from the Coma cluster of galaxies has traveled for approximately how long?

Accepted Answer

The light from the Coma cluster of galaxies has traveled for approximately 300 million years to reach Earth. This is because the Coma cluster is about 300 million light-years away from us, meaning light takes that long to travel from there to here.

Question 11

A spherical cluster of several hundred galaxies is found to contain far more ellipticals than spirals and irregulars. How would one classify this cluster?

Accepted Answer

The answer of A spherical cluster of several hundred galaxies...

Question 12

Why is the Coma cluster of galaxies a favorite among astronomers?

Accepted Answer

The Coma cluster is a favorite among astronomers because it is the rich, regular cluster nearest Earth, making it an excellent subject for study due to its relative proximity and the abundance of galaxies within it.

Question 13

What is a rich cluster of galaxies?

Accepted Answer

Rich clusters of galaxies are characterized by containing thousands of galaxies, distinguishing them from smaller groups or clusters with fewer members.

Question 14

Galaxies throughout the universe appear to be distributed

Accepted Answer

Galaxies are not distributed uniformly or centered around a single point. Instead, they are found in groups and clusters, which together form larger structures known as filaments. These filaments surround vast empty regions known as voids, creating a cosmic web-like structure throughout the universe. This distribution is a result of the gravitational forces acting over cosmic time scales, leading to the accumulation of matter in certain regions and the evacuation from others.

Question 15

What is the Local Group?

Accepted Answer

The Local Group is a galaxy cluster that includes the Milky Way among roughly 50 other galaxies, indicating a collection of galaxies rather than stars or a formation related specifically to the Andromeda Galaxy or a close group of stars.

Question 16

What is a poor cluster of galaxies?

Accepted Answer

A poor cluster of galaxies is defined as a cluster containing fewer than 1000 galaxies.

Question 17

Which of these characteristics does the Local Group of galaxies NOT have?

Accepted Answer

The Local Group is not dominated by a central giant elliptical galaxy; instead, it contains several large spiral galaxies, including the Milky Way and Andromeda, without a single dominating central giant elliptical galaxy.

Question 18

The relationship between a galaxy and the galaxy cluster of which it is a part is similar to the relationship between a galaxy cluster and the supercluster of which it is a part, with one important difference. What is that difference?

Accepted Answer

A cluster is a gravitationally bound system, meaning that the galaxies within it are held together by gravitational forces. A supercluster, on the other hand, is a larger-scale structure that is not gravitationally bound in the same way; it is more a grouping of clusters that are close in space but not necessarily bound by gravity.

Question 19

In which of these cases does gravity, a long-range force, NOT result in a bound system?

Accepted Answer

The answer of In which of these cases does gravity,...

Question 20

Suppose astronomers were able to detect radio signals from an intelligent civilization in the Coma cluster of galaxies. If they were to send a message to this civilization, how long would it take to get a reply?

Accepted Answer

The Coma Cluster is approximately 300 million light-years away from Earth. Therefore, a message sent to the Coma Cluster would take 300 million years to reach its destination, and an equal amount of time for the reply to return, totaling 600 million years.

Quiz 17: Galaxies