The development of structure in shearing, viscous media. II

An approximate algebraic method is presented for determining when local, self-gravitating structures can develop in viscous, shearing media, such as disks that may be generated by computer simulation. The principal advantage of the technique is that it does not require the numerical solution of the linear differential equations. This is seen as being of signal importance in the present context, since the general local problem considered here is characterized by five independent parameters. It is shown that the vorticity modes can grow spectacularly in viscous disks. Indeed, with significant shear viscosity, the familiar density waves damp strongly and only vortices survive. Therefore, 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.