MHD simulations of jet acceleration from Keplerian accretion disks

Abstract

Accretion disks and astrophysical jets are used to model many active astrophysical objects, viz., young stars, relativistic stars, and active galactic nuclei. In this paper we present self-consistent time-dependent simulations of supersonic jets launched from magnetized accretion disks, using high resolution numerical techniques. In particular we study the effects of the disk magnetic resistivity, parametrized through an alpha-prescription, in determining the properties of the inflow-outflow system. Moreover we analyze under which conditions steady state solutions of the type proposed in the self similar models of Blandford and Payne can be reached and maintained in a self consistent nonlinear stage. We use the resistive MHD FLASH code with adaptive mesh refinement, allowing us to follow the evolution of the structure for a time scale long enough to reach steady state. A detailed analysis of the initial configuration state is given. We obtain the expected solutions in the axisymmetric (2.5D) limit. Assuming a magnetic field around equipartition with the thermal pressure of the disk, we show how the characteristics of the disk jet system, as the ejection efficiency and the energetics, are affected by the anomalous resistivity acting inside the disk.