If we could watch spiral arms from a telescope situated above the Milky Way over 500 million years, what would we see happen?
A) Stars will move through the spiral arms, bunching up closer as they pass through. Young hot stars will form and die within the arms before having a chance to move out.
B) The spiral arms will seem to "wind up", to wrap more and more tightly around the center of the Galaxy.
C) The spiral arms will eventually dissipate and fade away, since they are a temporary phenomenon that should only last for a million years or so.
D) The spiral arms will eventually unwind, as centripetal forces send the stars flying outwards into intergalactic space.

Question

Quizplus · Accepted Answer

If we could watch spiral arms from a telescope situated above the Milky Way over 500 million years, we would see stars moving through the spiral arms, bunching up closer as they pass through. We would also observe young hot stars forming and eventually dying within the arms before having a chance to move out. This is because the spiral arms are regions of higher density where new stars can form due to the compression of gas and dust. They also act as a gravitational trap, keeping young stars within their boundaries for a short period before releasing them into the rest of the galaxy.

B, C, and D are not accurate because the winding up or fading away of spiral arms and the unwinding of the arms are not supported by current understanding of the dynamics and lifespan of spiral arms.

If We Could Watch Spiral Arms from a Telescope Situated