Theory of magnetized accretion-ejection structures

Accretion-ejection are interdependent processes linking jet acceleration and collimation physics to the underlying accretion disk physics. In these systems, a large scale vertical magnetic field is assumed to thread the accretion disk, leading simultaneously to jet formation and the onset of a magnetic turbulence inside the disk, both inducing accretion. While the first analytical models have been published more than 25 years ago, the global understanding has constantly progressed, showing the dominant role of jets or winds in driving accretion. The concept of Jet Emitting Disk (JED) and Wind Emitting Disk (WED) has emerged in the theoretical side, while in the computational side configurations such as Magnetically Arrested Disk (MAD) and Standard And Normal Evolution (SANE) have been the focus of much attention. A direct comparison between these costly 3D numerical experiments and steady-state theory has finally become feasible. After describing the physics and general properties of JED/WED accretion-ejection configurations, I will argue that they provide the state-of-the-art mathematical description of their numerical counterparts, MAD/SANE. More efforts need however to be done in order to firmly assess this point. In any case, these two complementary approaches have unveiled the critical role played in as- trophysical systems by the radial distribution and its temporal evolution of the local disk mag- netization. Magnetic field dragging in accretion disks appears therefore to be the key ingredient allowing to understand hybrid disk configurations and outbursting cycles, such as those seen in X-ray binaries.