If spiral density waves were the only thing producing spiral arms, what result would be expected?

Question

Quizplus · Accepted Answer

Spiral density waves theory suggests that the spiral arms are regions of higher density moving through the disk of the galaxy, which can lead to the formation of stars and give the appearance of long, smooth spiral arms. This theory does not necessarily predict gas-free or dust-free arms, irregular patterns of short arms, or spiral arms in the halo component of galaxies.

If Spiral Density Waves Were the Only Thing Producing Spiral