The galaxy isn't a rigid spinning object though, it's composed of many stars acting under gravitational influences. Like our solar system, objects closer in wil

The galaxy isn't a rigid spinning object though, it's composed of many stars acting under gravitational influences. Like our solar system, objects closer in will orbit faster than objects further out. Rather than fixed structures, the arms are more like a standing wave of greater density. Some related links https://en.wikipedia.org/wiki/Density_wave_theory https://en.wikipedia.org/wiki/Density_wave_theory https://en.wikipedia.org/wiki/Galaxy_rotation_curve https://en.wikipedia.org/wiki/Galaxy_rotation_curve https://www.nature.com/articles/s41550-018-0627-5 https://www.nature.com/articles/s41550-018-0627-5