A processing ring model for SS433

THE wavelengths of the shifted optical lines in SS433 seem to show a periodic variability at a period of 160 ± 3 d (or a multiple integer thereof) 1,2 . We have suggested that such periodicity could arise if the lines were emitted from a precessing ring of matter orbiting around a massive black hole (BH) of mass M (ref. 3). We also suggested that SS433 may be located inside an old globular cluster 3 . We describe here, in principle, how such precession model may come about and what some of its observational constraints might be.