Predicted properties of OB + BH systems. The left panels shows the number of systems in the OB mass–BH mass plane (second row), OB mass–orbital period plane (third row), and OB mass–OB velocity semi-amplitude plane (fourth row) in logarithmic colouring and the other panels are projections of that onto one axis, i.e. the distribution of OB masses (first row left), BH masses (second row right), orbital periods (third row right), and OB star velocity semi-amplitudes (fourth row right), where emission-line stars are marked by white dots. We also show the properties of all dynamically confirmed OB + BH systems in the local group and of the WR + O systems in the SMC with WR masses as BH masses.