Development of structure in shearing, viscous media. II

In this paper we present an approximate, algebraic method for determining when local, self-gravitating structures can develop in viscous, shearing media, such as disks that may be generated by computer simulation. The great advantage of the technique is that it does not require the numerical solution of the linear differential equation. This is particularly important in the present context, since the general local problem considered here is characterized by five independent parameters. We show that the vorticity modes can grow spectacularly in viscous disks. Indeed, in the presence of significant shear viscosity, the familiar density waves damp strongly and only vortices survive. Thus, the growth of structure in circumstellar disks and in the solar nebula may have proceeded along fundamentally different lines from those of the density enhancements in the disks of galaxies