SS433: on the uniqueness of cool relativistic jets

The relativistic jets of SS433 are outstanding for their optical thermal radiation.The radiation is produced by small clouds ($10^8$ cm) whose lifetime is about $10^3$ times larger than the gas-dynamical crushing time. We show that the clouds reside in thermal and dynamical balance as long as they collisionally interact with the wind of the supercritical accretion disk. The interaction is caused by the precessional movement of the jets and takes place only in the sweep-out zone. Beyond the sweep-out zone the interaction ceases and optical jets just terminate. The cloud magnetic field amplified in course of movement through a medium could play a role in containing a cloud. Thus, the clue to the uniqueness of the optical jets of SS433 is thought to be their precessional movement, which provides an opportunity for collisional interaction of the clouds with the wind.