Distributions of wide binary stars in theory and in Gaia data: II. Reconstruction of sample probability density of true orbit sizes

Abstract

Wide binary stars are important for testing alternative models of gravitation in the weak-field regime and understanding the statistical outcomes of dynamical interactions in the general Galactic field. The Gaia mission's collection of weakly bound pairs of stars offers a unique opportunity to estimate the rate of survivors at separations above 7 KAU, where non-Newtonian components of gravitation may become important. The available Gaia-based catalogs of resolved binaries provide the projected angular separation between the components, while the physical semimajor axis is the parameter of interest. The problem of reconstructing the distribution of orbit sizes is complex and ill-posed, because the observed apparent separations are defined by a number of underlying physical parameters including semimajor axis, eccentricity, orbit orientation, and orbital phase. Methods of inverse reconstruction of the marginal distribution of semimajor axes from the available data are proposed and implemented with two different strategies, namely, a direct Monte Carlo mapping and inverse filtering with impulse updates without regularization. We find rather similar results from the two methods for the outlying tail of the distribution, suggesting that the rate of orbit sizes is a shallow declining function on a logarithmic scale. A finite rate of extremely wide binaries is implied.