It is estimated that approximately one third of the star systems in the Milky Way are binary or multiple, with the remaining two thirds being single stars.[1] The overall multiplicity frequency of ordinary stars is a monotonically increasing function of stellar mass. That is, the likelihood of being in a binary or a multi-star system steadily increases as the masses of the components increase. [2] Mass range Multiplicity frequency Average companions ≤ 0.1 M☉ 22%+6%−4% 0.22+0.06−0.04 ...