Magnetized Accretion‐Ejection Structures: 2.5‐dimensional Magnetohydrodynamic Simulations of Continuous Ideal Jet Launching from Resistive Accretion Disks

We present numerical magnetohydrodynamic (MHD) simulations of a magnetizedaccretion disk launching trans-Alfvenic jets. These simulations, performed in a2.5 dimensional time-dependent polytropic resistive MHD framework, model aresistive accretion disk threaded by an initial vertical magnetic field. Theresistivity is only important inside the disk, and is prescribed as eta =alpha_m V_AH exp(-2Z^2/H^2), where V_A stands for Alfven speed, H is the diskscale height and the coefficient alpha_m is smaller than unity. By performingthe simulations over several tens of dynamical disk timescales, we show thatthe launching of a collimated outflow occurs self-consistently and the ejectionof matter is continuous and quasi-stationary. These are the first eversimulations of resistive accretion disks launching non-transient ideal MHDjets. Roughly 15% of accreted mass is persistently ejected. This outflow issafely characterized as a jet since the flow becomes super-fastmagnetosonic,well-collimated and reaches a quasi-stationary state. We present a completeillustration and explanation of the `accretion-ejection' mechanism that leadsto jet formation from a magnetized accretion disk. In particular, the magnetictorque inside the disk brakes the matter azimuthally and allows for accretion,while it is responsible for an effective magneto-centrifugal acceleration inthe jet. As such, the magnetic field channels the disk angular momentum andpowers the jet acceleration and collimation. The jet originates from the innerdisk region where equipartition between thermal and magnetic forces isachieved. A hollow, super-fastmagnetosonic shell of dense material is thenatural outcome of the inwards advection of a primordial field.