Cygnus X-1 contains a 21-solar mass black hole -- implications for massive star winds

TL;DR

This paper refines the distance to Cygnus X-1, revealing a 21-solar mass black hole, which challenges existing models of stellar winds and massive star evolution in high-metallicity environments.

Contribution

It provides a more precise measurement of Cygnus X-1's distance and black hole mass, offering new constraints on stellar wind mass loss in massive stars.

Findings

Black hole in Cygnus X-1 is approximately 21 solar masses.

Refined distance measurement to Cygnus X-1 using radio astrometry.

High-mass black hole challenges existing stellar wind models.

Abstract

The evolution of massive stars is influenced by the mass lost to stellar winds over their lifetimes. These winds limit the masses of the stellar remnants (such as black holes) that the stars ultimately produce. We use radio astrometry to refine the distance to the black hole X-ray binary Cygnus X-1, which we find to be $2.22^{+0.18}_{-0.17}$ kiloparsecs. When combined with previous optical data, this implies a black hole mass of $21.2\pm2.2$ solar masses, higher than previous measurements. The formation of such a high-mass black hole in a high-metallicity system constrains wind mass loss from massive stars.