Cygnus X-1
= Cygnus X-1
{c}
A stellar black-hole binary with a massive stellar companion. A 2011 dynamical analysis combined optical photometry and spectroscopy with a <distance> constraint and inferred $14.8\pm1.0$ <solar masses> for the compact object. This is that study's historical estimate, not a claim about the latest measurement.<The Mass of the Black Hole in Cygnus X-1 by Jerome A. Orosz and others>[abstract and dynamical-model constraints]{ref}