ON THE MHD ORIGIN OF ONE-SIDED JETS

One-sideness in extragalactic radio sources is usually associated to t he relativistic Doppler beaming in jets symmetrically emerging from th e central core of an AGN (assumed as a massive compact object surround ed by an accretion disk). However, if the beams are MHD driven and the magnetic configuration in the core region is non-symmetric or has pec uliar symmetry properties, the acceleration efficiency can be very dif ferent on the two hemispheres of the accretion disk. This magnetic str ucture may occur if in the disk the field derives from the combination of two components with different origin: i) a dipole primordial magne tic field, ii) a quadrupolar dynamo driven magnetic field. If in the a ccretion process this multipolar configuration is preserved, in the ce ntral region it is found a structure with the toroidal magnetic field not reversing across the disk equatorial plane. This geometry allows s teady MHD outflow solutions only in one of the two hemispheres, with c onsequent intrinsic one-sideness of beams. A similar process could als o work for one-sided jets in young stellar objects.