Secular ring instability in the protoplanetary accretion disk (Q1185075)

The aim of the present paper is to show that an accretion disk, the material of which satisfies the Navier-Stokes equations of a compressible fluid, is secularly unstable to axisymmetric density disturbances even if Toomre's parameter \(Q\) is greater than one. This instability process, which can also be interpreted as negative diffusion, immediatly leads to the formation of rings in the accretion disk as an intermediate step in the formation of planets, at least for the outer gaseous ones. We believe that the same process is also responsible for the ringlet-structure of planetary rings.