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Chapter 23: Problem 11

T/F: Nearly all the galaxy mass in the Local Group is located in just two galaxies.

Short Answer

Expert verified
True. The Milky Way and Andromeda contain nearly all the galaxy mass in the Local Group.

Step by step solution

01

Understand the Statement

The exercise is asking whether nearly all the galaxy mass in the Local Group () is located in just two galaxies.
02

Key Galaxies in the Local Group

Identify the major galaxies in the Local Group. The two largest galaxies in the Local Group are the Milky Way and Andromeda galaxies. They both have significantly more mass compared to other galaxies in the group.
03

Evaluate the Mass Distribution

Consider the mass distribution of the Local Group. Since the Milky Way and Andromeda are the largest galaxies, it is plausible that nearly all the galaxy mass in the Local Group could be in these two galaxies.
04

Conclude the Statement

Based on the information above, the statement that nearly all the galaxy mass in the Local Group is located in just two galaxies—Milky Way and Andromeda—is true.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Milky Way
The Milky Way is one of the two largest galaxies in the Local Group. It's our home galaxy, and it contains our Solar System along with hundreds of billions of stars. The Milky Way is a spiral galaxy, characterized by its rotating disk of stars, gas, and dust. Understanding the structure of the Milky Way helps us grasp its immense scale and the variety of objects it contains.

Some key features of the Milky Way include:
  • The Galactic Center: This is the rotational center of the Milky Way, containing a supermassive black hole named Sagittarius A*.
  • The Disk: A flat region composed of stars, nebulae, and other celestial objects rotating around the Galactic Center.
  • The Halo: A spherical region surrounding the disk, containing older stars and globular clusters.
The mass of the Milky Way is substantial, estimated to be around one trillion solar masses. This significant amount of mass contributes heavily to the overall mass distribution in the Local Group.
Andromeda Galaxy
The Andromeda Galaxy is the other major galaxy of the Local Group. It is a spiral galaxy, similar in structure to the Milky Way. The Andromeda Galaxy is located approximately 2.5 million light-years from the Milky Way, and it is the largest galaxy in the Local Group by physical size.

Key characteristics of the Andromeda Galaxy:
  • Stellar Population: Andromeda is thought to contain about one trillion stars, making it slightly larger than the Milky Way in terms of stellar content.
  • Interacting Companion Galaxies: Andromeda has several smaller galaxies orbiting it, including M32 and M110.
  • Movement Toward the Milky Way: Andromeda is on a collision course with the Milky Way, and they are expected to merge in about 4.5 billion years.
The Andromeda Galaxy's mass is also approximately one trillion solar masses, similar to that of the Milky Way. Together, these two galaxies dominate the mass distribution in the Local Group, making the assertion in the exercise accurate.
Galactic Mass Distribution
Galactic mass distribution refers to how mass is spread out across different galaxies within a group or cluster. In the case of the Local Group, the Milky Way and Andromeda Galaxies account for nearly all the group's total mass.

Let's delve into why this is the case:
  • Mass Dominance: The Milky Way and Andromeda each have masses around one trillion solar masses. Other galaxies in the Local Group, like the Triangulum Galaxy and various dwarf galaxies, have significantly less mass.
  • Gravitational Influence: Due to their massive sizes, the Milky Way and Andromeda have substantial gravitational pulls, which can impact the orbits and behaviors of smaller nearby galaxies.
  • Dark Matter: Both galaxies contain large amounts of dark matter, an unseen substance that accounts for most of the mass in galaxies and affects their gravitational interactions.
Understanding galactic mass distribution is crucial to studying the dynamics and evolution of galaxy groups. It helps explain why most of the mass in the Local Group is concentrated in just two galaxies, providing insight into gravitational relationships and the future interactions between these colossal bodies.

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Most popular questions from this chapter

Dark matter cannot consist of neutrons, protons, and electrons, because if it did, a. the abundances of isotopes would not be the same as those observed. b. it would have interacted with light in the early universe. c. stars and galaxies would be much more massive. d. both a and b

What is the primary difference between galaxy groups and galaxy clusters? a. the volume they occupy b. the number of galaxies c. the total mass of the galaxies d. all of the above

Use your favorite search engine to find the highest-redshift galaxy, quasar, and GRB observed so far. Why are astronomers interested in finding objects at higher and higher redshifts? Why is it also important for astronomers to estimate the relative frequency of such objects, compared to the frequency at \(z=6\) or \(z=2 ?\)

What are some of the observational signs that dark matter exists?

T/F: Hot dark matter cannot account for the formation of today's galaxies.
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