Distributions of wide binary stars in theory and in Gaia data: III. Orbital momenta, masses, and manifestations of MOND

TL;DR

This study analyzes Gaia DR3 binary star data to examine orbital momenta, mass distributions, and test for Modified Newtonian Dynamics (MOND) effects, finding no evidence of MOND in the observed parameters.

Contribution

It introduces a new observable, the projected orbital momentum, and models the mass distribution of wide binaries using Gaia data, testing MOND predictions.

Findings

The mass density model fits the observed orbital momentum distribution well.

Widest binaries tend to include more solar-type primaries.

No manifestation of MOND is detected in the data.

Abstract

Using the censored catalog of 103,169 resolved Gaia DR3 binary stars with accurate astrometric data for each component, a new observable, object-specific parameter is computed for each pair: the projected orbital momentum. This parameter is the product of four functions of physical characteristics: total mass, semimajor axis, eccentricity, and inclination angle. Using the previously estimated marginal probability densities of eccentricity and semimajor axis, and assuming an isotropic orientation of binary systems, the sample distribution of mass was adjusted using a concordance metric of the observed and synthetic distributions of orbital momenta and an ad hoc functional model. The best-fitting mass density model is found to faithfully reproduce the observed dependence of orbital momenta on apparent separation, although the absolute luminosity distributions indicate a tendency of the widest systems to more frequently include solar-type primaries. The anticipated manifestation of MOND is computed in the investigated parameter space \{separation, momentum\}. This effect is absent in the given data. The median total mass of the widest Gaia binaries is found to be somewhat higher than that of the tighter pairs, which is interpreted as a dynamical age effect.