Explorations: An Introduction to Astronomy (Arny), 7th Edition

Chapter 17: Galaxies

Questions for Review

1
What are the three main types of galaxies? How do the basic galaxy types differ in shape, stellar content, and interstellar matter?
2
Why is it not surprising that elliptical galaxies contain mostly Pop II stars?
3
Explain several ways astronomers measure the distance to nearby galaxies. Why is it important to know the distance?
4
What is the Hubble law? In what situations does Hubble's law not apply?
5
Why are galaxy collisions of interest?
6
What happens to the stars when two galaxies collide?
7
What are the three main types of active galaxies? List the main characteristics of each.
8
Sketch of a radio galaxy illustrating its structure. Why do astronomers call these objects "radio" galaxies?
9
What process generates the radio emission in radio galaxies?
10
What is the evidence that quasars are very distant?
11
How is it known that active galaxies have small core regions?
12
What mechanism has been suggested as powering active galaxies?
13
How might a large black hole form in a galaxy's core?
14
What is the Local Group, and why is it a group and not a cluster?
15
What are some differences between clusters that contain large and small numbers of galaxies?
16
What is the Local Supercluster? How many clusters might be in a supercluster and how big is one?
17
What is a void?
18
What does the large-scale structure of the Universe look like? How do astronomers study it?
19
How do astronomers measure the mass of a galaxy?
20
What is meant by dark matter? What observations support its existence? What types have been proposed?
21
What is a gravitational lens? What can observations of lenses tell us about clusters?
22
What is the apparent ratio of dark matter to normal matter in a typical galaxy? In a cluster of galaxies?
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