The helical structure of radio jets in quasars and active cores of galaxies.

Magnetohydrodynamic wind instability in a supersonic relativistic magnetized beam could induce helical boundary perturbations with characteristic wavelengths and azimuthal numbers that are consistent with the wavy contours observed in many radio-galaxy jets. Calculations are performed which indicate that resonance splitting should have little effect on this instability behavior. A diagram is presented of a cylindrical jet with a wavy boundary, illustrating the mutual orientation of the ambient flow-velocity vectors, the magnetic field, and the direction of wave propagation.