Robust Evidence for the Breakdown of Standard Gravity at Low Acceleration from Statistically Pure Binaries Free of Hidden Companions

Kyu-Hyun Chae

Published 2023-09-19Version 1

It is found that Gaia DR3 binary stars selected with stringent requirements on astrometric measurements and radial velocities naturally satisfy Newtonian dynamics without hidden close companions when projected separation $s > 2$ kau, showing that pure binaries can be selected. It is then found that pure binaries selected with the same criteria show a systematic deviation from the Newtonian expectation when $s < 2$ kau. When both proper motions and parallaxes are required to have precision better than 0.003 and radial velocities better than 0.2, I obtain 1558 statistically pure binaries within a 'clean' $G$-band absolute magnitude range. From this sample, I obtain an observed to Newtonian predicted kinematic acceleration ratio of $\gamma_g=g_{\rm{obs}}/g_{\rm{pred}}=1.43^{+0.23}_{-0.19}$ for acceleration $< 10^{-10}$ m s$^{-2}$, in excellent agreement with a recent finding $1.43\pm 0.06$ for a much larger general sample with the amount of hidden close companions self-calibrated. I also investigate the radial profile of stacked sky-projected relative velocities without a deprojection to the 3D space. The observed profile matches the Newtonian predicted profile for $s < 2$ kau without any free parameters but shows a clear deviation at a larger separation with a significance of $4.6\sigma$. The projected velocity boost factor for $s>8$ kau is measured to be $\gamma_{v_p} = 1.18\pm 0.06$ matching $\sqrt{\gamma_g}$. Finally, for a small sample of 23 binaries with exceptionally precise radial velocities (precision $<0.0043$) the directly measured relative velocities in the 3D space also show a boost at larger separations. These results robustly confirm the recently reported gravitational anomaly at low acceleration for a general sample.