Limit orbital speed (v_lim) as a function of mass for a star that is about to experience complete collapse in a binary system. The limit orbital speed determines the minimum relative orbital speed a star in a binary must have in order to merge within the age of the Universe (black lines). For a given binary system, a natal kick $f_{\mathrm{kick}}\ge \sqrt{3}$ will lead to a retrograde orbit (blue lines) and a natal kick above $f_{\mathrm{kick}}\ge 1+\sqrt{2}$ will disrupt the binary (red lines). The characteristic speed depends on the mass ratio (q := M₂/M₁), which I consider to be either q = 0.1 (dashed lines) or q = 1 (solid lines).