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Chapter 23: Problem 23

Do density waves form a stationary pattern in a galaxy? If not, do they move more rapidly, less rapidly, or at the same speed as stars in the disk?

Short Answer

Expert verified
No, density waves do not form a stationary pattern in a galaxy, and they move at a different speed compared to the stars in the disk. The speed can be either more or less than that of the stars.

Step by step solution

01

- Understanding Density Waves

In a spiral galaxy, density waves are supposed to cause the arm like patterns we see. These are not stationary and move at a different speed from stars.
02

- Comparing the speed of Density Waves and Stars

The individual stars in the galaxy actually move in elliptical orbits that take them in and out of the spiral arms. The arms themselves, made visible by a higher density of stars, are density waves and move at a different speed.
03

- Conclusion on Density Waves

Therefore, density waves do not form a stationary pattern in a galaxy, and they move at a different speed compared to the stars in the disk. The speed can be more or less than the speed of the stars, it varies.

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Most popular questions from this chapter

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

The galactic halo is dominated by Population II stars, whereas the galactic disk contains predominantly Population I stars. In which of these parts of the Galaxy has star formation taken place recently? Explain.

Show that the form of Kepler's third law stated in Box 23-2, \(P^{2}=4 \pi^{2} a^{3} / G\left(M+\mathrm{M}_{\odot}\right)\), is equivalent to \(M=r v^{2} / G\), provided the orbit is a circle. (Hint: The mass of the Sun (M \(\mathrm{M}_{\odot}\) ) is much less than the mass of the Galaxy inside the Sun's orbit (M).)

The disk of the Galaxy is about \(50 \mathrm{kpc}\) in diameter and 600 pc thick. (a) Find the volume of the disk in cubic parsecs. (b) Find the volume (in cubic parsecs) of a sphere \(300 \mathrm{pc}\) in radius centered on the Sun. (c) If supernovae occur randomly throughout the volume of the Galaxy, what is the probability that a given supernova will occur within \(300 \mathrm{pc}\) of the Sun? If there are about three supernovae each century in our Galaxy, how often, on average, should we expect to see one within \(300 \mathrm{pc}\) of the Sun?

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