Astronomers used high‑resolution FLAMES‑ARGUS spectra taken at several epochs. By applying spectral disentangling, they were able to separate the blended light into two separate stellar spectra.

The analysis found a primary star of about 1.7 M⊙ and a rapidly rotating companion of about 5.2 M⊙, giving a mass ratio of roughly 3.3. The system’s light is dominated by the secondary, which contributes about 35–50 % of the red‑optical flux measured by FLAMES, higher than the 10 % limit from earlier MUSE data.

Broad‑band photometry from Hubble was used to fit the spectral energy distributions of the two stars. The derived radii (6.7 R⊙ for the primary, 4.1 R⊙ for the secondary) match the temperatures and gravities from the spectroscopic fit.

These findings rule out the presence of a dark compact object. The measured system velocity and mass function imply an inclination of less than about 67°, which is consistent with the derived masses.

However, uncertainties remain. The surface gravities of both stars are not tightly constrained, and the limited resolution and signal‑to‑noise of the FLAMES data introduce degeneracies in effective temperature and rotation. The large flux contribution of the secondary relative to previous data could be caused by a nearby fainter star, an optically thick disc, or an unresolved tertiary companion. Finally, the analysis assumes solar‑scaled abundances; previous mass transfer could have altered the chemical composition of the stars.

While the current results strongly disfavor a black hole in NGC 1850‑BH1, further observations at higher resolution and with more precise orbital constraints would tighten the parameters and test the remaining uncertainties.