Where Do Eccentric Stellar Twins Come From?

"Widely separated binary systems take more than a thousand years to complete a single orbit, making it challenging to measure the eccentricity of an individual system. Instead, Hsiang-Chih Hwang (Institute for Advanced Study) used a statistical technique to study nearly a million binary systems at once. Using stellar position and velocity data from Gaia, the team measured the angle between two vectors: one that describes the difference in the binary members’ motion across the sky (v) and one that connects the two stars (r)."