Corner plot showing the BH mass, the companion mass, the orbital period, and the eccentricity of binaries in a default POSYDON population synthesis run with enhanced WR wind (factor = 1.3); see the text for more details. The grey histograms are the full population, and the green ones are limited to binaries with orbital periods of up to 5 000 days. The observationally determined values for the Gaia BHs are shown in colour (El-Badry et al. 2023a,b; Gaia Collaboration 2024). It should be noted that the histograms are weighted to represent the number of such binaries in the MW, which has large uncertainties as given by the unity unit $[1_{-1.0}^{+3.3}]$; for details see Appendix D.