Recently, by using the LAMOST spectra, Prof. Wei-Min Gu (Xiamen University) and his collaborators have published a paper in Astrophysical Journal Letters (ApJL, 872, L20) on a new method to search for stellar-mass black hole candidates.

Based on the stellar spectra of LAMOST Data Release 6, a sample of seven giants in binaries is obtained with large radial velocity variation (> 80 km/s). With the effective temperature, surface gravity, and metallicity provided by LAMOST, and the parallax given by Gaia, the mass and radius of the giant can be estimated, and therefore the mass of the optically invisible star in the binary can be evaluated. The paper shows that the sources in the sample are potential black hole candidates, and are worthy of dynamical measurement by further spectroscopic observations. The proposed method is particularly valid for the selection of black hole candidates with unknown orbital periods. Moreover, the ongoing LAMOST Medium Resolution Survey is quite helpful to select a large number of black hole candidates with such a method.

Figure. Comparison of the observations (blue circles) with the theoretical results (lines) in the DVR 2 - log g diagram, where M2？=？3 M☉is adopted for the theoretical calculations.