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Chapter 23: Problem 22

What is the winding dilemma? What does it tell us about the nature of spiral arms?

Short Answer

Expert verified
The winding dilemma is a concept in astronomy that explores the nature of spiral arms in galaxies, questioning why they do not wind tightly over time given their differential rotation. Its resolution led to the conclusion that the arms of a spiral galaxy are not material entities, but rather areas of higher star density, resulting from density waves that move through the galaxy.

Step by step solution

01

Understanding the Winding Dilemma

First, it is important to understand the concept of the winding dilemma. It is a theory in astronomy which contradicts the observation that spiral galaxies maintain their spiral shape over long periods of time. According to the winding dilemma, if spiral arms were solid structures, they should wind up into a tight coil as the galaxy rotates because the inner parts of the galaxy rotate faster than the outer parts.
02

Clarifying the Nature of Spiral Arms

Next, understand what this tells us about the nature of spiral arms. This issue led astronomers to reconsider the nature of spiral arms. Instead of being permanent structures, spiral arms are now considered to be density waves. Density waves are regions of increased density that move through the galaxy, triggering star formation.
03

Understanding the Outcome of the Dilemma

Understand what findings resulted from the winding dilemma. Astronomers' understanding of the nature of spiral arms led to the density wave theory, which solved the winding dilemma by explaining why spiral arms do not wind up over time. In the density wave theory, stars move in and out of the density wave, preserving the arm's overall shape but continually changing its constituents.

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Most popular questions from this chapter

\(\mathrm{O}\) or \(\mathrm{B}\) main-sequence stars are found in the galactic disk but not in globular clusters. Why is this so?

In what way are the orbits of stars in the galactic disk different from the orbits of planets in our solar system? What does this difference imply about the way that matter is distributed in the Galaxy?

Sketch the rotation curve you would obtain if the Galaxy were rotating like a rigid body.

Another student tells you that the Milky Way Galaxy is made up "mostly of stars." Is this statement accurate? Why or why not?

Discuss how a supermassive black hole could have formed at the center of our Galaxy.
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