What initial challenge baffled astronomers regarding spiral arms due to differential rotation?
Answer
The winding problem, causing arms to coil rapidly
The winding problem described the physical impossibility of long-lived spiral arms existing if they were composed of fixed material. Differential rotation dictates that matter closer to the galactic center orbits significantly faster than material farther away. If the arms were permanent physical structures made of the same stars and gas throughout, this differential speed would cause them to tighten and coil extremely quickly, making them essentially invisible after only a few galactic rotations. This rapid winding effect presented a major conundrum that required a new theoretical framework to resolve, leading to the understanding that the arms are dynamic patterns, not static structures.
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