What dynamic mechanism is responsible for compressing material in spiral arms to trigger star formation?

Answer

Density waves compressing the interstellar medium

Spiral arms are formed by density waves that sweep through the galactic plane, compressing clouds of cold molecular gas and dust, which leads to gravitational collapse and star formation.

What dynamic mechanism is responsible for compressing material in spiral arms to trigger star formation?
galaxyastronomyspiral galaxygasdust