Introduction

With VLBI techniques it is possible to map the inner part of SS433 downto the size where one can see evolutionary effects. Blobs of accellerated and collimated gas are ejected from the core at a speed of in two anti-paralllel directions. Due to precession of the inner system the radio blobs show a corcscrew shaped trail. On scales smaller than 0.5 arcsec discrete features in the radio beams are dominant.

Most of the radiation arises on scales larger than cm (15 mas). Blobs are often, but not always, ejected in two opposite directions. They have a tendancy to brighten at a substantial distance from the core ( cm), and then they fade rapidly. This brightening zone could occur when a new blob overtakes the bowshock of its predecesor. With this mechanism it is possible to produce the brightening zone at a well defined position without a special requirement of the medium surrounding SS433.