No Gravitational Anomaly in Wide Binaries from Forward Modeling of 3D Orbits

Abstract

Recent work by Chae et al. (2026) reported a gravitational anomaly in 36 wide-binary pairs, finding a gravity boost factor of $\gamma \equiv G_{\mathrm{eff}}/G_{\mathrm{N}}\approx 1.60_{-0.14}^{+0.17}$ at low accelerations, consistent with predictions from Modified Newtonian Dynamics (MOND). We reanalyze the same dataset using a hierarchical Bayesian model that infers a global $\gamma$ across all systems while fitting three-dimensional orbital elements. Our model yields $\gamma =1.00_{-0.19}^{+0.24}$, consistent with Newtonian gravity ($\gamma =1$). To identify the source of the discrepancy, we perform a test using an approach similar to Chae et al. (2026), replacing the semi-major axis with a geometric de-projection of the observed projected separation. This test yields $\gamma =1.56_{-0.18}^{+0.21}$, closely matching the result of Chae et al. (2026). This shows that if the three-dimensional orbital separation is forward modeled using an independent semi-major axis parameter and then projected into the space of the observables, the relative velocities of wide binaries are consistent with Newtonian gravity.

12 pages, 9 figures, 1 table. Published in the Open Journal of Astrophysics