Probing the nature of gravity in the low-acceleration limit: wide binaries of extreme separations with perspective effects

TL;DR

This study extends the analysis of wide binary stars to larger separations, finding gravitational acceleration boosts at low accelerations consistent with modified gravity theories like MOND, challenging Newtonian predictions.

Contribution

It provides new observational evidence at larger separations, incorporating perspective effects, supporting modified gravity models over dark matter explanations.

Findings

Gravitational boost factor $oldsymbol{ extgamma_g}$ increases at low accelerations.

Results align with predictions of MOND-like modified gravity theories.

Perspective effects are significant and properly accounted for in the analysis.

Abstract

Recent statistical analyses of wide binaries have revealed a boost in gravitational acceleration with respect to the prediction by Newtonian gravity at low internal accelerations $\lesssim 10^{-9}$ m\,s$^{-2}$. This phenomenon is important because it does not permit the dark matter interpretation, unlike galaxy rotation curves. We extend previous analyses by increasing the maximum sky-projected separation from 30 to 50 kilo astronomical units (kau). We show that the so-called ``perspective effects'' are not negligible at this extended separation and, thus, incorporate it in our analysis. With wide binaries selected with very stringent criteria, we find that the gravitational acceleration boost factor, $\gamma_g \equiv g_{\rm obs}/g_{\mathrm N}$, is $1.61^{+0.37}_{-0.29}$ (from $\delta_{\rm obs-newt}\equiv (\log_{10}\gamma_g)/\sqrt{2}=0.147\pm0.062$) at Newtonian accelerations $g_{\mathrm N} = 10^{-11.0}$ m\,s$^{-2}$, corresponding to separations of tens of kau for solar-mass binaries. At Newtonian accelerations $g_{\mathrm N} = 10^{-10.3}$ m\,s$^{-2}$, we find $\gamma_g=1.26^{+0.12}_{-0.10}$ ($\delta_{\rm obs-newt}=0.072\pm0.027$). For all binaries with $g_{\rm N}\lesssim10^{-10}$ m\,$s^{-2}$ from our sample, we find $\gamma_g=1.32^{+0.12}_{-0.11}$ ($\delta_{\rm obs-newt}=0.085\pm0.027$). These results are consistent with the generic prediction of MOND-type modified gravity, although the current data are not sufficient to pin down the low-acceleration limiting behavior. Finally, we emphasize that the observed deviation from Newtonian gravity cannot be explained by the perspective effects or any separation-dependent eccentricity variation which we have taken into account.