Over the past couple of years a clear gravitational anomaly has been reported and confirmed by two independent research groups carefully considering relative velocities, v and separations, s, on the plane of the sky, for wide binary star samples from the most recent GAIA catalogue. Over various studies covering a range of sample selection strategies
and statistical analysis techniques, a surprising phenomenology has emerged. While the small separation samples for s<2000 au accurately conform to Newtonian expectations, for separations above 3000 au, a clear and systematic departure from Newtonian predictions appears. This high separation regime shows a v proportional to s^(-1/2) scaling, but corresponding to Keplerian orbits under an effective gravitational constant of 1.5G. Given the narrow range of total masses of around 1.6 M_{sun} in the samples considered, the critical separation at which a change in regime appears corresponds to approaching the a0 threshold, where a0 is the characteristic acceleration scale of MOND, as inferred from galactic rotation curve observations. Further, the precise distribution of wide binary relative velocities measured, closely corresponds to MOND expectations for such solar neighbourhood systems under the external field effect predicted by MOND.
Now that a low acceleration validity limit for Newtonian gravity has been found, precisely at the acceleration scales over which the presence of dark matter has been proposed, astrophysical inferences for such hypothetical components become suspect.
