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Researchers from the Xinjiang Astronomical Observatory (XAO) of the Chinese Academy of Sciences have made significant progress in understanding how three-dimensional (3D) layered structures form within open star clusters. Using N-body simulations and analyzing 279 nearby open clusters in the solar neighborhood, the researchers identified a strong correlation between the number of member stars and the presence of spatial stratification.

The findings, in Astronomy & Astrophysics, indicate that clusters with fewer stars generally lack layered structures, while those with more than 100 members are more likely to exhibit spatial layering.

Follow-up simulations demonstrated that the initial binary star fraction and the mass of the most massive star are key parameters influencing whether stratification emerges within a cluster.

Open clusters are gravitationally bound systems of stars formed from the same molecular cloud and share similar ages and chemical compositions. Therefore, they serve as ideal natural laboratories for studying the process of stellar formation and evolution. While previous studies have highlighted differences between the cores and outskirts of star clusters, their internal 3D layered structures and the underlying physical mechanisms remain poorly understood.

To address this gap, the researchers investigated the dominant factors influencing the formation of such spatial structures from a dynamical perspective, using N-body simulations. Their results show that massive stars (with masses exceeding 8 solar masses) drive strong mass loss via supernova explosions and stellar winds, which weakens the layered structure in the core region.

Meanwhile, binary systems delay core collapse and suppress stratification through energy equipartition, gravitational disturbances, and dynamical friction. In high binary-fraction models, the cluster becomes more isotropic, and the layered structure nearly disappears.

This study not only highlights the crucial roles of massive stars and binary systems in the structural evolution of open clusters, but also provides a new dynamical framework for understanding their formation and development.

With increased observational data and expanded sample sizes, future research will aim to further validate these simulation results and deepen our understanding of the stellar system evolution in the Milky Way. The researchers also plan to investigate additional cluster samples to test and refine the theoretical models.