Detection of Gravitational Anomaly at Low Acceleration from a Highest-quality Sample of 36 Wide Binaries with Accurate 3D Velocities

Abstract

We set out to accurately measure gravity in the low-acceleration range $(10^{-11},10^{-9})\mathrm{m}{\mathrm{s}}^{-2}$ from 3D motions of isolated wide binary stars. Gaia DR3 provides precise measurements of the four sky-plane components of the 3D relative displacement and velocity ($\mathbf{r},\mathbf{v}$) for a wide binary, but not comparably precise line-of-sight (radial) separation and relative velocity $v_r$. Based on our new observations and the public databases/publications, we assemble a sample of 36 nearby (distance $<150$pc) wide binaries in the low-acceleration regime with accurate values of $v_r$ (measurement uncertainty $<100$ m\,s${}^{-1}$). Kinematic contaminants such as undetected stellar companions are well under control using various observational diagnostics such as Gaia's {\tt ruwe} parameter, the color-magnitude diagram, multi-epoch observations of radial velocities, Speckle interferometric follow-up observations, and requiring Hipparcos-Gaia proper motion consistency. For the parameter $\Gamma \equiv {\log }_{10}\sqrt{\gamma }$ with $\gamma \equiv G/G_{\mathrm{N}}$ (where $G$ is a parameter generalizing Newton's constant $G_{\mathrm{N}}$ in elliptical orbits), we find $\Gamma =0.102_{-0.021}^{+0.028}$ for $<10^{-9.1}\mathrm{m}{\mathrm{s}}^{-2}$ ($0.132_{-0.027}^{+0.035}$ for $<10^{-9.5}\mathrm{m}{\mathrm{s}}^{-2}$) giving a gravity boost factor of $\gamma =1.60_{-0.14}^{+0.24}$, which rules out Newton and is higher than relevant MOND predictions. This strong anomaly is dominated by two systems (the pairs of HD 189739, HD 189760, and TYC 259-236-1, TYC 259-906-1) that have 3D relative velocities exceeding their estimated Newtonian escape velocities but are unlikely to be chance associations or contaminated systems. (abridged)

41 pages (main part) + 39 pages (appendix), revised version for the AAS journals