LB-1 is a binary star which some analysis has suggested includes a stellar-mass black hole larger than thought possible, but other observations and analysis suggest otherwise. The visible star is a B-type star, and based upon the characteristics of such stars and their brightness and the implied distance, its mass and radial velocity measurements through spectrography imply an orbit with some unseen massive object, such as a quiet black hole. Gaia measurement of its distance (by parallax) suggests it is much closer, and alternative theories that are consistent with the Gaia-determined distance have been investigated. Clear characteristics:
Based upon the black hole theory:
Gaia's distance determination is 2.14 kpc, and theories have been developed in which one or both the stars together produce LB-1's spectral features; one such theory suggesting inclusion of a Be star.