COLLIMATION OF ASTROPHYSICAL JETS BY INERTIAL CONFINEMENT

MANY astrophysical objects, from young stars, Herbig-Haro objects and planetary nebulae up to active galactic nuclei, can be very simply modelled as isotropic sources of high-energy tenuous gas embedded in dense toroidal clouds. Here we describe numerical simulations showing how such an arrangement can in general circumstances give rise to a well collimated jet, as is observed in many of these systems. Our model is a two-dimensional generalization of the interacting-winds description of planetary nebulae. Where the two winds come into contact, a discontinuity is formed, which is dragged out by the fast outflowing gas into a chimney along the polar axis. High-energy gas rushes up this channel and flows out around the top, creating a hot backflow which keeps the chimney in place. The inner shock, enclosing the source of the fast wind, also aids in collimation, and ionization cones such as those observed in active galactic nuclei may also form.