If you are referring to the vortical shell emcompassing the spiral arm of the Cat's eye nebula, this is similar to the vortrex of a singular vortex that has occurred in an outward inversed manner.
In the spiral arm, viscous mass of heavier matter is vortically pushed out through the vortex column, and disspiates at the tip of the vortex column on higher altitude by scattering the heavier matter vortically on higher atmosphere in lighter density viscous mass. These haverier matter falls back on the spiral arm in a folding manner back to lower atmosphere vortically therefore organises as a shell encompassing the spiral arm.
Earth have a magnetic tail phenomenon that is pushed away from the direction of Sun and then fold back similar to the spiral arm of Cat's eye nebula.
I can visualize this is the force dynamics that pushes up volcanoe on stratified surface that has encased the molten matter of a suspended spheroid and causes volcanoe erruption.
Thanks for your inspiring responds.