Gravitational Anomaly Measurement in Wide Binaries is Sensitive to Orbital Modeling

TL;DR

This study reevaluates gravitational anomalies in wide binary systems, demonstrating that the inferred gravity boost factor is highly sensitive to orbital modeling assumptions, and finds results consistent with Newtonian gravity.

Contribution

We introduce a hierarchical Bayesian model that accounts for orbital uncertainties, revealing the importance of orbital modeling choices in gravitational anomaly measurements.

Findings

Our model finds γ ≈ 1.12, consistent with Newtonian gravity.

Replacing semi-major axis with projected separation yields γ ≈ 1.56, matching previous anomalous results.

Orbital modeling assumptions significantly influence the inferred gravitational anomalies.

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.