Gravitational Anomaly Measurement in Wide Binaries is Sensitive to Orbital Modeling

Abstract

Recent work by Chae et al. (2026) reported a gravitational anomaly in 36 wide-binary pairs, finding a gravity boost factor of $\gamma \equiv G_{\rm eff}/G_{\rm N} \approx 1.60_{-0.14}^{+0.17}$ 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 $\gamma = 1.12^{+0.27}_{-0.22}$, consistent with Newtonian gravity ($\gamma = 1$) at the $\sim0.4\sigma$ level. 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 $\gamma = 1.56^{+0.21}_{-0.18}$, closely matching the result of Chae et al. (2026). This suggests that the inferred value of $\gamma$ is sensitive to how the three-dimensional orbital separation is modeled, and including an independent semi-major axis parameter can account for velocity excesses that would otherwise be attributed to non-Newtonian gravity.