In these objects, over-reflection can cause excitations called WASERs.
In these objects, over-reflection can cause excitations called WASERs. Sheer forces and self-gravity cause swing, which is another method of amplifying waves in these objects. One form of resonance in these objects has the difference between the pattern and corotation speeds equal to an integer multiple of the epicyclic frequency. That Lindblad resonance occurs in a quasi-steady density wave theory of these objects, and that theory, developed by Lin and Shu explained the winding problem. The rotation velocity of these objects increases with luminosity according to the Tully-Fischer relation. These objects can have bright lines called bars running through them. FTP, name these galaxies, exemplified by Andromeda and the Milky Way.
In these objects, over-reflection can cause excitations called WASERs.
spiral galaxies [prompt on partial answer]