NGC 300 X-1 is a Wolf–Rayet/black hole binary.

We present Very Large Telescope/FORS2 time-series spectroscopy of the Wolf–Rayet (WR) star #41 in the Sculptor group galaxy NGC 300. We confirm a physical association with NGC 300 X-1, since radial velocity variations of the He iiλ4686 line indicate an orbital period of 32.3 ± 0.2 h which agrees at the 2σ level with the X-ray period from Carpano et al. We measure a radial velocity semi-amplitude of 267 ± 8 km s⁻¹, from which a mass function of is obtained. A revised spectroscopic mass for the WN-type companion of yields a black hole mass of for a preferred inclination of . If the WR star provides half of the measured visual continuum flux, a reduced WR (black hole) mass of ) would be inferred. As such, #41/NGC 300 X-1 represents only the second extragalactic WR plus black hole binary system, after IC 10 X-1. In addition, the compact object responsible for NGC 300 X-1 is the second highest stellar-mass black hole known to date, exceeded only by IC 10 X-1. [ABSTRACT FROM AUTHOR]