Influence of selection criteria on the interpretation of rotational behaviour of wide-binary star systems

Abstract

Binary star systems are expected to follow Newtonian dynamics similarly to planetary systems. However, reports have been made of wide binary systems with separations around 0.01 pc and larger, showing potential deviations from standard Newtonian motion. This phenomenon, suggestive of the flattening of galactic rotation curves, calls for closer inspection. This study presents an analysis of wide binary stars using data from Gaia Data Release 3 (DR3), a space-based astrometry mission funded by the European Space Agency. The study compares different choices of selection criteria to examine the nature of these apparent anomalous kinematics within the solar neighbourhood. The Gaia data set furnishes detailed parameters, including radial velocity, mass, age, and binary probability in addition to standard parameters. A custom Python tool named BYNARY facilitated both data processing and analysis. This report reveals that the signs of any anomalous signals systematically diminish as the initial selection criteria are relaxed for degrouping while subsequent filtering remains stringent, leading to the complete elimination of any apparent non-Newtonian motion for binary separations within 0.5 pc. The study shows that an y observ ed anomalous behaviour in solar neighbourhood wide binaries within 130 pc must be produced either by faint companion stars orbiting primary or secondary stars, or by flyby stars. The findings emphasize the importance of the choice of selection criteria in disentangling genuine binary dynamics from external influences. The conclusions align with the predictions of Newtonian mechanics and general relativity, though they do not exclude other phenomena at larger scales.