The collimation of magnetized winds

Abstract

It is established that any stationary axisymmetric magnetized wind will collimate along the symmetry axis at large distances from the source. This result is proved by consideration of the asymoptotic properties of the transfield equation, keeping the exact conserved quantities along field lines. The only consistent nonsingular solution with a nonvanishing poloidal current approaches a cylindrical structure. For singular solutions or those with a vanishing poloidal current, the asymptotic solutions can be paraboloidal. This result only applies to pure wind boundary conditions on the surface of the source. It is shown how the boundary conditions and the critical point analysis are related in our asymptotic analysis. This result demonstrates that axisymmetric magnetized flows tend generally to collimate, and it is hypothesized that this is the natural reason why there are so many collimated flows and jets.