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We examine the distribution of on-sky relative velocities for wide binariespreviously assembled from GAIA DR2 data and focus on the origin of the highvelocity tail of apparently unbound systems which may be interpreted asevidence for non-Newtonian gravity in the weak field limit. We argue that thistail is instead explicable in terms of a population of hidden triples, i.e.cases where one of the components of the wide binary is itself a close binaryunresolved in the GAIA data. In this case the motion of the photocentre of theinner pair relative to its barycentre affects the apparent relative propermotion of the wide pair and can make pairs that are in fact bound appear to beunbound. We show that the general shape of the observed distributions can bereproduced using simple observationally motivated assumptions about thepopulation of hidden triples.

The distribution of relative proper motions of wide binaries in GAIA DR2: MOND or multiplicity?