Massive stellar-mass black holes are not expected in a Galactic metallicity environment, owing to strong stellar winds and pair-instability supernovae. In this context, the recent report1 of an approximately 70-solar-mass (M☉) black hole in the galactic binary system LB-1 challenges conventional theories of massive-star evolution, stellar winds and core-collapse supernovae, thus requiring a more exotic scenario to explain the existence and properties of this system2, 3. Here we show that the apparent shifts of the Hα emission line used to derive the mass of the black hole arise from the orbital motion of the B-type companion star in the LB-1 binary system and not from that of the black hole. No evidence for a massive black hole remains in the data, thus removing the existing tension between its proposed existence and models of the formation of such a massive black hole at galactic metallicity. LB-1 is a recently discovered galactic spectroscopic binary system with a 78.9-day period. Using multi-epoch optical spectroscopy from the LAMOST and Keck telescopes, Liu et al. 1 recently reported the detection of a 68− 13+ 11 M☉ black hole paired with an 8.2− 1.2+ 0.9M☉ B-type subgiant star. This black hole is over twice as massive as any other known stellar-mass black hole with non-compact companions4, 5 and its mass approaches the masses that result from mergers of black holes detected by gravitational wave interferometers6. The detection of a large black-hole mass relies on two main lines of evidence:(1) the characterization of the orbital and physical properties of its companion B-type-star; and (2) an indirect measurement of the reflex orbital motion of the black hole. The critical measure that yields the high mass for the hidden companion comes from the semi-amplitude KBH= 6.4 km s− 1 of the radial-velocity curve of this potential black hole, a result that is measured from the apparent wobbling of the position of the wings of the Hα emission profile, assuming that this emission is generated by a passive accretion disk around the unseen companion. Although Liu et al. 1 assumed that such wobbling was tracing the reflex motion of the black hole, we show here that the observed radial-velocity measurements result from the superposition of the stellar absorption line of the B-type star on a static Hα emission profile. This can be demonstrated either observationally or solely by simulation.

To reach this conclusion, we used new high-spectral-resolution observations of LB-1 obtained with the HERMES spectrograph7 coupled with the Mercator telescope on the island of La Palma, Spain (see Supplementary Information). Using these data, we isolated the pure Hα emission profile by subtracting from the observed profile a theoretical Hα absorption profile corresponding to the best-fit atmospheric parameters of the detected B-type star (see Supplementary Information), after accounting for the orbital shift of the observed