Does a Rotation Velocity Jump Generate the Outer Spiral Structure?

We investigate a stability of the gaseous disk in the Milky Way. The rotation curve with smooth two kinks in the Solar vicinity (Fig.1) was adopted in accordance with the observations (Fridman et al., 1994a). Such a gaseous disk is unstable. The instability can generate the four-armed spiral (Fig.2) and four-vortex structure (Fig.3). The method of the analysis is described by Fridman et al., 1994b. The generation mechanism is similar to that described by Glatsel, 1987.