Open star clusters are some of the most dazzling objects in the sky. The small ones contain a few dozen stars, while the largest contain several thousand. The stars cluster together because they all formed from the same giant molecular cloud. Astronomers don't know exactly how many open clusters (OC) there are. There are more than 5,000 confirmed clusters, and possibly as many as 100,000. They're difficult to see because so many are obscured by thick dust in the galactic plane. OCs are identified visually, and also by their ages, metallicities, and movement. The Gaia mission, which catalogued 2 billion objects—mostly stars—added to our understanding of open clusters immensely. Just like stars, open clusters can be in binary relationships with one another. New research in Astronomy and Astrophysics aimed to understand these binary clusters better, hoping to shed light on how many of them form, their gravitational interactions, and their physical properties.…