Unstable Spiral Modes in Disk-Shaped Galaxies: Enhancement of Growth Rate

An additional effect not considered in our earlier papers is found to enhance the rate of growth of spiral modes in disk-shaped galaxies. This enhanced growth appears to be attributable to the combined influence of differential rotation and tangential forces. For certain galaxy models, rapid temporal growths are possible (comparable to those found in numerical experiments), but in many real galaxies, these tendencies to extreme growth rates are probably reduced to lower levels by competing effects such as wave absorption at inner Lindblad resonance.