On the formation and propagation of interstellar jets

The flow that results from stationary supersonically converging conical streams is studied by means of two dimensional numerical calculations. Convergency leads to a “colimator” conical shock and this to the formation of an underexpanded hydrodynamical jet. The properties of the conical shock and of the collimated stream are summarized for a variety of initial conditions. The resultant jets are followed to large distances (≥7.5×1017 cm) away from the injection point, and are shown to develop a complicated structure that eventually approaches a stationary state. Stationary features such as crossing shocks are shown to evolve from working surface shocks, left behind the head of the jet to ensure self-collimation of the beam matter. Transient, as opposed to stationary, supersonically converging conical streams are also shown to generate collimator shocks, and under special conditions, long-lasting hydrodynamical jets and bipolar flows. Such flows are shown to emanate from compact disc funnels, if they are suddenly inmersed into a thermal bath. These calculations suggest that in many cases, the outflow phenomena (e.g. HH objects, jets and bipolar molecular flows) may simply be signaling the disruption of the compact discs, out of which exciting stars form.