2008A&A...491..671T

A self-organizational view of planetary nebulae, driven by global conservation properties of the magnetohydrodynamic (MHD) plasma, is presented. Self-similarity with a self-consistent evolution function is used, as a method and as a model for self-organized states, to solve the time-dependent MHD equations in the gravitational field of a central star. The self-similar configurations are constructed on the basis of a limited radially expanding MHD plasma sphere, which could be associated with the ejected hydrogen layer of the AGB star due to its strong pulsations. Although the plasma expansion velocity is isotropically radial, driven by self-organization, the interactions between the conducting plasma and the magnetic fields steer the MHD system to a highly inhomogeneous spatial distribution. This spatial redistribution involves the focusing of magnetic energy, plasma thermal energy, and plasma momentum, generating collimated jets, point-symmetric knots, and circulating filaments.