Course 4: Accretion-Ejection Models of Astrophysical Jets

Abstract.

Astrophysical jets are almost always associated with accreting objects, be they young stellar objects or massive black holes. Their role in the evolution of accretion disks is tied to the effciency with which hydromagnetic flows can transport angular momentum from their sources. These lectures constitute a review of the latest developments in the observation, theory, and numerical simulation of astrophysical jets. Among the most basic results in this field is the observed relation between the jet mass loss rate and the disk accretion rate $\dot{M}_w/\dot{M}_a \simeq 0.1$ which is observed in many different systems and arises in numerical simulations of all kinds. This connection is a consequence of angular momentum extraction from the disk by magneto-centrifugal winds. These systems can be regarded as integrated accretion-ejection structures - a notion that is explored in some detail. This paper also presents new results on numerical simulations of 2D and 3D jets for a wide variety of initial magnetic configurations. Astrophysical jets are shown to have both highly collimated as well as wide-angle outflow characteristics, and they are robustly stable in 3D.