A team of Indian astronomers led by researchers from Gauhati University and the Indian Institute of Astrophysics has redefined the star cluster UBC 63, previously identified as a single entity, as actually consisting of two distinct star clusters designated UBC 63A and UBC 63B. The discovery was made using data from the European Space Agency's Gaia mission, which provides precise measurements of stellar positions and motions across the Milky Way.
The research revealed that the two clusters have markedly different ages, with UBC 63A being approximately 21 million years old while UBC 63B is much older at about 562 million years, indicating they did not originate as a single cluster. Through detailed analysis using machine learning techniques and advanced dynamical simulations, the team determined that the two clusters underwent a close flyby approximately 6 million years ago, coming within about 7 parsecs (23 light years) of each other. Currently, the clusters are approximately 26 parsecs (85 light years) apart and are moving away from each other rather than being gravitationally bound.
The study, published in the Astronomical Journal, demonstrates the power of modern astronomical surveys to uncover hidden structures that remain unnoticed when stars are viewed only in projection on the sky. This rare detection of a system soon after a close encounter provides valuable clues about how gravitational interactions influence cluster structure, motion, and long-term evolution in the Milky Way.