How does density wave theory explain the formation and persistence of spiral arms in galaxies?
Answer
Gravitational forces create a ripple effect that compresses gas and triggers star formation
Density wave theory compares spiral arms to a traffic jam on a highway. In this analogy, the cars represent gas and stars, while the traffic jam represents the arm. The cars flow into the jam from behind, move through it, and exit the other side; the jam itself persists even as the individual cars change. Gravitational forces create a compression wave that travels through the galaxy, forcing gas to bunch up and collapse, which results in the birth of bright, hot stars that define the visible spiral arms.
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