Rotationally supported disks are easily prone to long-lived bar instabilities.
Bars undergo secular evolution related to the dynamical stability of the galaxy as a whole.
REAL Automated Morphological Classification. The figure at the top of this page illustrates some current efforts in this direction. UGC 6693, the linear bar structure is well reproduced. Additionally, rather subtle spiral features are faithfully reproduced in the model images. Six Fourier terms are used in each of the 7 elliptical annuli, resulting in a model vector having 84 numerical values.