Wind mass-loss rates of stripped stars inferred from Cygnus X-1

Understand

Recent observations of the high-mass X-ray binary Cygnus X-1 have shown that both the companion star (41 solar masses) and the black hole (21 solar masses) are more massive than previously estimated.

• Furthermore, the black hole appears to be nearly maximally spinning.
• Here we present a possible formation channel for the Cygnus X-1 system that matches the observed system properties.
• In this formation channel, we find that the orbital parameters of Cygnus X-1, combined with the observed metallicity of the companion, imply a significant reduction in mass loss through winds relative to commonly used prescriptions for stripped stars.