Poynting jets from accretion disks: Magnetohydrodynamic simulations

The powerful narrow jets observed to emanate from many compact accreting ob jects may arise from the twisting of a magnetic field threading a different ially rotating accretion disk that acts to extract magnetically the angular momentum and energy from the disk. Two main regimes have been discussed, h ydromagnetic outflows, which have a significant mass flux and which have th e energy and angular momentum carried by both the matter and the electromag netic field, and Poynting outflows, in which the mass flux is negligible an d the energy and angular momentum are carried predominantly by the electrom agnetic field. Recent simulation studies have focused almost exclusively on hydromagnetic outflows. Here we consider a Keplerian disk initially thread ed by a dipole like poloidal magnetic field. We present the first MHD simul ation results establishing that a quasi-stationary collimated Poynting jet arises from the inner part of the disk while a steady uncollimated hydromag netic outflow arises in the outer part of the disk.