The answer that I gave is perhaps a little thin on the electrical effects that go into the formation of galaxies. The reason is that I do not understand much about how this side of things works. I need to go and read the old guys on the subject of electricity. People like J J Thomson and Steinmetz. People operating before the influence of team-Einstein and the Jew takeover ruined all our understanding of electricity and physics generally. Here is my answer:
The important thing to understand is that gravity has not had a scientifically valid update in more than 300 years. Its very evident now that it does not operate as advertised. In reality gravity is such that large objects like to orbit and not to crash. There are hundreds of millions of large objects all having some sort of gravitational attraction to each other. Yet no known crashes.
So orbits are very robust. Moons grow to planets grow to stars. Stars to bigger stars. Our sun may have been once a planet revolving around one of the big Orion stars. Looking at a single spiral arm I would assume that the very largest stars are in the centre of these bands. With generally smaller stars revolving around them. And these smaller stars, at any one time, being toward the outside of the spiral arm. So its kind of natural that over time that these bands would form. The spiral arms will never unwind. Because the velocity will be equalised between adjacent bands, because of these gravitational tendencies towards robust orbits and non-collision.
The solar wind amounts to an electrical current with a powerful positive charge. So there ought to be an electrical repulsive force between two stars that is not present between a star and a planet. This could well have a segregating effect on these bands.