We have seen that the disks of spiral galaxies contain stars that move in circles in the same direction around the central bulge. the disks contain many bright blue stars that have formed recently, giving them their distinct colors. the disks also often contain bright spiral-shaped arms with darker regions in between. how are these arms related to the stars?

Stars are formed on the density waves and the waves have gases and stellar winds that aid in there formation.

Explanation:

As the spiral galaxies are those that are formed by the flat rotating disks that have stars, dust and lots of gas and the concentration of the tars is called the bulge. They are surrounded by a fainter halo and globular clusters.  They have the wide arms that extend from the center of the galactic disk and have ongoing star formations. As they have many loose arms that have young and hot stars and are blue in color and that makes them so bright.