Editing Cygnus X-1 (section)

====Formation====
The largest star in the Cygnus&nbsp;OB3 association has a mass 40 times that of the Sun. As more massive stars evolve more rapidly, this implies that the progenitor star for Cygnus&nbsp;X-1 had more than 40 solar masses. Given the current estimated mass of the black hole, the progenitor star must have lost over 30 solar masses of material. Part of this mass may have been lost to HDE&nbsp;226868, while the remainder was most likely expelled by a strong stellar wind. The [[helium]] enrichment of HDE&nbsp;226868's outer atmosphere may be evidence for this mass transfer.<ref name=mnras341_2_385/> Possibly the progenitor may have evolved into a [[Wolf–Rayet star]], which ejects a substantial proportion of its atmosphere using just such a powerful stellar wind.<ref name=science300_5622_1119/>

If the progenitor star had exploded as a [[supernova]], then observations of similar objects show that the remnant would most likely have been ejected from the system at a relatively high velocity. As the object remained in orbit, this indicates that the progenitor may have collapsed directly into a black hole without exploding (or at most produced only a relatively modest explosion).<ref name=science300_5622_1119/>