The supercritical accretion disk in SS433 and ultraluminous X-ray sources

SS433 is the only known persistent supercritical accretor in our Galaxy, and it may be very important for understanding ultraluminous X-ray sources (ULXs) located in external galaxies. We describe the main properties of the SS433 supercritical accretion disk, jets, its radio nebula W50 and compare them with known properties of ULXs and their nebulae. We discuss the supercritical disk radiation spectrum in SS433, which is hidden for direct observations, and find it mat be similar to the ULX spectra. Our spectral observations of the ULX nebulae show that nebulae have to be powered by their central black holes. The nebulae are shocked and dynamically perturbed probably by jets.