Poynting jets from accretion disks: Magnetohydrodynamic simulations

The powerful narrow jets observed to emanate from many compact accreting objects may arise from the twisting of a magnetic field threading a differentially rotating accretion disk that acts to extract magnetically the angular momentum and energy from the disk. Two main regimes have been discussed, hydromagnetic outflows, which have a significant mass flux and which have the energy and angular momentum carried by both the matter and the electromagnetic field, and Poynting outflows, in which the mass flux is negligible and the energy and angular momentum are carried predominantly by the electromagnetic field. Recent simulation studies have focused almost exclusively on hydromagnetic outflows. Here we consider a Keplerian disk initially threaded by a dipole like poloidal magnetic field. We present the first MHD simulation results establishing that a quasi-stationary collimated Poynting jet arises from the inner part of the disk while a steady uncollimated hydromagnetic outflow arises in the outer part of the disk.