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Register a new userInternal kinematics of GAIA eDR3 wide binaries
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Using the recent GAIA eDR3 catalogue we construct a sample of solar neighbourhood isolated wide binaries satisfying a series of strict signal-to-noise data cuts, exclusion of random association criteria and detailed colour-magnitude diagram selections, to minimise the presence of any kinematic contaminating effects having been discussed in the literature to date. Our final high-purity sample consists of 421 binary pairs within 130 pc of the sun and in all cases high-quality GAIA single-stellar fits for both components of each binary (final average RUWE values of 0.99), both also restricted to the cleanest region of the main sequence. We find kinematics fully consistent with Newtonian expectations for separations, $s$, below 0.009 pc, with relative velocities scaling with $Delta V propto s^{-1/2}$ and a total binary mass, $M_{b}$, velocity scaling of $Delta V propto M_{b}^{1/2}$. For the separation region of $s> 0.009$ pc we obtain significantly different results, with a separation independent $Delta V approx 0.5$ km/s and a $Delta V propto M_{b}^{0.22 pm 0.18}$. This situation is highly reminiscent of the low acceleration galactic baryonic Tully-Fisher phenomenology, and indeed, the change from the two regimes we find closely corresponds to the $a lesssim a_{0}$ transition.
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Under Newtonian dynamics, the relative motion of the components of a binary star should follow a Keplerian scaling with separation. Once orientation effects and a distribution of ellipticities are accounted for, dynamical evolution can be modelled to include the effects of Galactic tides and stellar mass perturbers, over the lifetime of the solar neighbourhood. This furnishes a prediction for the relative velocity between the components of a binary and their projected separation. Taking a carefully selected small sample of 81 solar neighbourhood wide binaries from the {it Hipparcos} catalogue, we identify these same stars in the recent Gaia DR2, to test the prediction mentioned using the latest and most accurate astrometry available. The results are consistent with the Newtonian prediction for projected separations below 7000 AU, but inconsistent with it at larger separations, where accelerations are expected to be lower than the critical $a_{0}=1.2 times 10^{-10} $ { m s$^{-2}$} value of MONDian gravity. This result challenges Newtonian gravity at low accelerations and shows clearly the appearance of gravitational anomalies of the type usually attributed to dark matter at galactic scales, now at much smaller stellar scales.
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