Binary fraction, defined as the number of binaries over the total number of objects, normalized by the bin width. The black points are data for the ONC from Duchêne et al. (1825). The black histogram shows f_b for the spatially not constrained region, that is Gaia DR2 data with C1 and C2 selections. The gray dashed histogram shows the data only for the central part that is the same as in the study by Scally et al. (1999). The last bin showing wide binaries in the range 1000−3000 au represents newly discovered potential binaries that seemed to be absent (Scally et al. 1999) (see Fig. 8). The limit 3000 au is motivated by the beginning of the elbow in Fig. 7.