Chapter 15: Problem 28
Why do disk stars bob up and down as they orbit the galaxy? (a) because the gravity of other disk stars always pulls them toward the disk (b) because of friction with the interstellar medium (c) because the halo stars keep knocking them back into the disk.
Short Answer
Expert verified
Disk stars bob up and down due to the gravitational pull of other disk stars.
Step by step solution
01
Understanding the Structure of a Galaxy
Stars in a galaxy are primarily found in three components: the disk, the halo, and the bulge. Disk stars are those that orbit within the thin plane of the galaxy disk. This disk is flat and contains most of the galaxy’s gas, dust, and younger stars.
02
Gravitational Influence on Disk Stars
Disk stars move in nearly circular orbits around the center of the galaxy. However, their motions are not perfectly planar; they exhibit an up-and-down motion while orbiting. This occurs because the gravitational force of the stars in the disk pulls each star back towards the plane of the galaxy when it moves above or below it.
03
Addressing the Options
(a) suggests the gravity of other disk stars pulls them toward the disk: this is accurate as gravity is the primary force maintaining their vertical oscillations. (b) suggests friction with the interstellar medium: disk stars do not experience significant friction that would cause the bobbing motion. (c) involves the influence of halo stars: halo stars are not numerous or close enough to knock disk stars consistently back into the disk.
04
Conclusion
Based on our analysis, option (a) is correct. The up and down motion of disk stars is due to the gravitational pull of other stars in the disk, which keeps them oscillating around the plane of the disk.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Disk Stars
Disk stars are fascinating and form a substantial part of a galaxy's structure. They move within the flat, circular area of the galaxy known as the disk. This region houses most of the galaxy's gas, dust, and young stars. Disk stars travel in the thin plane of this disk, making them different from stars located in other components like the halo or the bulge. The disk itself is relatively thin compared to the vast breadth of the galaxy, and its flat shape is where these stars orbit around the galactic center.
These stars are typically younger than those in other components of the galaxy, like the halo. Their orbits in the disk are relatively stable, following near-circular paths around the center of their galaxy.
These stars are typically younger than those in other components of the galaxy, like the halo. Their orbits in the disk are relatively stable, following near-circular paths around the center of their galaxy.
Gravitational Influence
Gravity plays a vital role in the movement of disk stars within a galaxy. As disk stars travel through their orbits, they often move slightly above and below the plane of the disk. This bobbing motion is primarily due to the gravitational influence of other stars within the disk. When a star moves away from the central plane, gravitational forces from surrounding stars pull it back towards the disk's midline. This interaction keeps stars oscillating, or bobbing up and down, around the galactic plane.
- Gravity is the force that maintains the vertical oscillation of disk stars.
- It prevents stars from flying off into space and keeps them within the confines of the disk.
Galactic Components
Understanding galactic components is essential for comprehending the structure of a galaxy. A galaxy is composed of several key components:
- Disk: This is the flat, circular region where disk stars, gas, and dust reside.
- Halo: A spherical area surrounding the galaxy's disk that hosts older stars and globular clusters.
- Bulge: Found at the galaxy's center, this region is densely populated with stars and can have a rounded, somewhat flattened shape.
Orbital Motion
Orbital motion is a fundamental aspect of galaxy dynamics, especially for stars within the disk. Disk stars orbit the galaxy's center in a manner that is primarily circular. This circular motion allows for a stable and consistent path around the galactic core. However, the motion is not entirely confined to the two-dimensional plane, as stars also bob up and down while orbiting. This bobbing occurs due to gravitational interactions that we previously discussed.
Understanding the orbital motion involves recognizing that:
Understanding the orbital motion involves recognizing that:
- Stars maintain velocity to balance gravitational pull from the galaxy’s core.
- Up-and-down motions result from gravitational influences within the disk.