Magnetic collimation of meridional-self-similar general relativistic MHD   flows
  We present a model for the spine of relativistic MHD outflows in the Kerr geometry. Meridional self-similarity is invoked to derive semi-analytical solutions close to the polar axis. The study of the energy conservation along a particular field line gives a simple criterion for the collimation of jets. Such parameter have already been derived in the classical case by Sauty et al. 1999 and also extended to the Schwarzschild metric by Meliani et al. 2006. We generalize the same study to the Kerr metric. We show that the rotation of the black hole increases the magnetic self-confinement. 
Noemie Globus, Christophe Sauty, V\'eronique Cayatte, Ludwik M.   Celnikier
astro-ph.HE