Internal kinematics of GAIA DR3 wide binaries: anomalous behaviour in the low acceleration regime

Abstract

The {\it Gaia} eDR3 catalogue has recently been used to study statistically the internal kinematics of wide binary populations using relative velocities of the two component stars, $\Delta V$, total binary masses, $m_B$, and separations, $s$. For $s\gtrsim 0.01$ pc, these binaries probe the low acceleration $a\lesssim 2a_0$ regime where gravitational anomalies usually attributed to dark matter are observed in the flat rotation curves of spiral galaxies, where $a_0\approx 1.2\times 10^{-10}$m s${}^{-2}$ is the acceleration scale of MOND. Such experiments test the degree of generality of these anomalies, by exploring the same acceleration regime using independent astronomical systems of vastly smaller mass and size. A signal above Newtonian expectations has been observed when $a\lesssim 2a_0$, alternatively interpreted as evidence of a modification of gravity, or as due to kinematic contaminants; undetected stellar components, unbound encounters or spurious projection effects. Here I take advantage of the enhanced DR3 {\it Gaia} catalogue to perform a more rigorous study of the internal kinematics of wide binaries than what has previously been possible. Internally determined {\it Gaia} stellar masses and estimates of binary probabilities for each star using spectroscopic information, together with a larger sample of radial velocities, allow for a significant improvement in the analysis and careful exclusion of possible kinematic contaminants. Resulting $\Delta V$ scalings accurately tracing Newtonian expectations for the high acceleration regime, but markedly inconsistent with these expectations in the low acceleration one, are obtained. A non-Newtonian low acceleration phenomenology is thus confirmed.

16 pages, 10 figures. Accepted for publication in MNRAS

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