Numerical simulations of the accretion-ejection instability

The Accretion-Ejection Instability (AEI) is explored numerically using a global 2d model of the inner region of a magnetised accretion disk. The disk is initially currentless but threaded by an external vertical magnetic field created by external currents, and frozen in the flow. In agreement with the theory a spiral instability, similar in many ways to those observed in self-gravitating disks, but driven by magnetic stresses, develops when the magnetic field is close to equipartition with the disk thermal pressure. The present non-linear simulations give good evidence that such an instability can occur in the inner region of accretion disks.