Spiral arms would be dispersed too quickly by the orbital speeds' varying with radial distance. Some process needs to be maintaining them. http://en.wikipedia.o

Spiral arms would be dispersed too quickly by the orbital speeds' varying with radial distance. Some process needs to be maintaining them. http://en.wikipedia.org/wiki/Spiral_galaxy#Origin_of_the_spiral_structure http://en.wikipedia.org/wiki/Spiral_galaxy#Origin_of_the_spi...