Density Waves and the Stability of Galactic Spiral Arms

Awesome animation!!! I had the idea to make an animation of exactly what you have here, but never got around to making it. I had it all planned out perfectly in my head but, as with many of my visions, it never leaves the play ground of my mind. :-)

whats your definition of stable? able to inhabit life?

Stable as in you see the shape of the spirals even though there are stars (solar systems) continually moving into and out of the spirals (this is the point of the animation). If the spirals only consisted of the same stars, then the spirals would "wrap up" around the galactic core and would essentially smear out of visibility.