The reconfinement of jets

Abstract

The 'reconfinement shoulder' of the jets in several extragalactic radio sources appears to be a typical property of jets observed with sufficiently high resolution to map the structure transverse to the jet axis. While this may be due to the rapid decrease of internal pressure in a free jet with distance from the nucleus, so that the jet should come into pressure equilibrium with an ambient medium, it is noted that the highly supersonic character of the flow in free jets entails that the reconfinement process be accompanied by shocks. The structure of inviscid, steady state jets in the presence of a realistic ambient medium is presently calculated by means of the method of characteristics, establishing that the reconfinement is accompanied by conical shocks which heat the jet and thereby cause it to reexpand as a free jet. The jet shape typically observed can be reproduced by this process.