Indian astronomers find the open cluster UBC 63 is really two clusters that passed close by each other

5 November 2026

A team led by Gauhati University and the Indian Institute of Astrophysics has shown that UBC 63, long treated as one loose open star cluster, is in fact two separate clusters. They have been named UBC 63A and UBC 63B. The group was studying star formation in the cluster using data from the European Space Agency's Gaia mission when colour-magnitude diagrams showed two distinct stellar sequences. Machine learning and dynamical simulations confirmed two populations. UBC 63A is about 21 million years old while UBC 63B is about 562 million years old, and the cluster lies about 4,892 light years away. The two systems came within about 7 parsecs of each other roughly 6 million years ago and are now about 26 parsecs apart and drifting away. They are not bound to each other by gravity. The work appeared in The Astronomical Journal. The Indian Institute of Astrophysics is an autonomous institution of the Department of Science and Technology.