New Advances Transform Identification of Milky Way’s Sibling Star Clusters
- Ritambhara K
- 7 hours ago
- 2 min read
Stars are born in clusters, and these clusters themselves often emerge in pairs or small groups. Among them, binary clusters—pairs of open clusters that are tightly linked in both position and motion—hold particular importance. Their formation preserves the imprint of how stars take shape inside giant molecular clouds, making these cluster pairs valuable tracers of star formation processes and the evolutionary pathways of stellar systems.
In a significant advancement for Galactic astronomy, PhD candidate LIU Guimei and her supervisor Prof. ZHANG Yu from the Xinjiang Astronomical Observatory (XAO), Chinese Academy of Sciences, together with collaborators from the Shanghai Astronomical Observatory (SHAO), have conducted one of the most comprehensive systematic investigations of binary open clusters in the Milky Way to date.
Using the exceptional precision of the Gaia satellite’s astrometric data and applying rigorous, uniform selection methods, the team assembled an extensive sample of binary cluster candidates, ultimately confirming 400 such systems, including 268 that had not been previously reported. Their findings have been published in Astronomy & Astrophysics.
The researchers examined nearly 4,000 high-quality open clusters using Gaia DR3 astrometry and kinematics, establishing a robust statistical framework to quantify spatial and velocity proximity between cluster pairs.
This method was carefully validated against randomized mock samples to ensure reliability. Using this framework, the team identified 400 candidate binary clusters and organized them into three distinct categories: primordial (co-natal) binary clusters, tidal- or resonant-capture binary clusters, and optical pairs, which are simply chance alignments along the line of sight.
The analysis reveals that 61% of these candidates share highly consistent ages and kinematic properties, strongly suggesting they were born together from the same giant molecular cloud. Additionally, 83% exhibit clear signs of tidal interaction, and the strength of these interactions correlates strongly with spatial separation—the closer the clusters are, the more pronounced their mutual gravitational influence.
Overall, the study estimates that about 17% of all open clusters in the Milky Way are currently part of binary or multiple-cluster systems, and roughly 10% likely formed as primordial binary clusters. These proportions align closely with previous observational and theoretical expectations.
This work introduces a unified, well-defined system for identifying and classifying binary clusters within our Galaxy. It highlights the potential importance of hierarchical star formation—where clusters themselves form in structured, interconnected environments—and provides crucial observational evidence for understanding the origins and dynamical evolution of multi-cluster systems. The research supports a broader, multi-scale view of star formation in the Milky Way.
The study received highly positive feedback during peer review, with one anonymous referee noting, “This is a good paper that offers new insights into a topical issue.” The research was supported by the National Natural Science Foundation of China, the Chinese Academy of Sciences, and regional funding from Xinjiang.
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