Gaia Data Uncovers Four Substuctures within Open Cluster NGC 752

By analyzing the data from ESA's Gaia satellite, Chinese astronomers have investigated the structure of a nearby open cluster known as NGC 752. The new study identified four substructures and delivered evidence for mass segregation in this cluster. The findings were presented Jan. 12 on the arXiv preprint server. Open clusters (OCs) are groups of stars formed from the same giant molecular cloud and loosely gravitationally bound to each other. Astronomers are interested in exploring the structures of OCs in detail as such studies could be crucial for improving our understanding of the formation and evolution of our galaxy. A disintegrating cluster with tidal tails NGC 752, also known as Caldwell 28, is an intermediate-age (about 1.4 billion years old) OC in the constellation Andromeda, some 1,400 light years away. The cluster contains at least 300 members—mainly low-mass stars on the main sequence or red giants. The mass of NGC 752 is estimated to be approximately 297 solar masses. Previous observations of NGC 752 have found that it is a disintegrating cluster with tidal tails extending on either side of its central region. More recent observations of NGC 752 suggest that these tidal tails may extend much further than previously thought. Therefore, a team of astronomers led by Delong Jia of the Beijing Normal University in China decided to investigate NGC 752's tidal tails and the cluster's overall structure. For this purpose, they analyzed the data from Gaia's Data Release 3 (DR3). "Using Gaia DR3 data, we applied a hierarchical clustering algorithm to the open cluster NGC 752 based on the kinematical information and identified four substructures corresponding to different stages of disintegration," the researchers write. Four substructures The newfound substructures, designated Sub 1-Sub 4, were identified at different levels of gravitational binding. In general, it turned out that NGC 752 has a relatively dense core (Sub 1), and the outer substructures are being gradually stripped away. According to the study, Sub 1 is located in the cluster's central region and represents a high-density core. Sub 2 appears to be primarily distributed in the west and also includes some stars spatially close to the core. When it comes to Sub 3, it lies mainly to the east, with its members extending away from the cluster, while in contrast, Sub 4 appears more diffuse, consists of weakly bound members, and contains a tidal tail extending to the southeast. The masses of the substructures from 1 to 4 were calculated to be 245.2, 26.3, 27.9, and 33.1 solar masses, respectively. Therefore, the total mass of the cluster was estimated to be 332.5, which is higher than previously thought. Mass segregation The study also found evidence for mass segregation in NGC 752. The results clearly indicate that lower-mass stars are more likely to be distributed in the outer regions of the cluster, which is consistent with the typical phenomenon of mass segregation. "This suggests that NGC 752 may have undergone a period of internal dynamical evolution," the authors of the paper conclude. © 2026 Science X Network