The Hydrodinamical Mechanism of Jets’ Formation and Collimation in Young Star Objects

The results of numerical hydrodynamical simulation of shock shells evolution in young star objects are presented. We have shown that during the expanding process of such shell, a slowly rotating supersonic collimated jet made of accretion disk substance forms inside the shell through the development of consequence “ejection — thorus — tornado — jet”. The mechanism of outflow’s forming and collimation is only hydrodynamical and based on the conservation law of angular momentum. It must work for all accretion-jet systems. Additional factors (such as magnetic fields) can modify such mechanism, but not eliminate it. Let’s list the main conclusions: 1) The jet is formed from the substance of the circumstellar disc. It has an angular momentum co-ordinated with the symmetry axis of the system. 2) If a one-sided ejection of matter takes place, then the shock wave, caused by it, passes through a thin circumstellar disk. Then it forms a shock wave (shell) on the other side of the disk. 3) At high initial ejection velocities, there is a significant elongation of the head of the shell. This is typical for many observable young star objects. 4) The formation of the jet is due to the presence of a long-lived torus-like vortex, in which the gas rotates both along the toroidal axis and around it.