SS 433 is hosted by the Milky Way. It is a remarkable microquasar and eclipsing X-ray binary in the constellation Aquila, about 18,000 light-years away and located inside the supernova remnant W50.
The system contains a stellar-mass compact object, generally modeled as a black hole, that accretes matter from an A-type companion star. The infalling material forms a hot accretion disk that produces intense X-rays. SS 433 also launches two opposing jets of matter moving at about 26% of the speed of light.
Its name comes from the catalog compiled by astronomers Nicholas Sanduleak and Charles Stephenson: SS 433 was their 433rd entry for a star with strong emission lines. “Microquasar” describes its resemblance to quasars on a much smaller scale. The alternatives are other galaxies, but SS 433 is a Galactic system, not an extragalactic object.