A study published in Astronomy & Astrophysics has revealed four previously unidentified primordial open cluster (OC) groups in the Milky Way.

Open clusters—loosely bound groups of stars formed from the same giant molecular cloud (GMC)—are generally thought to originate in isolation. However, the newly identified OC groups each consist of multiple clusters derived from a common GMC, produced through sequential star formation.

Of particular interest, two of these groups, labeled G1 and G2, appear to have formed through a hierarchical process triggered by multiple supernova (SN) explosions.

Researchers from the Xinjiang Astronomical Observatory (XAO) of the Chinese Academy of Sciences, in collaboration with the Shanghai Astronomical Observatory, Yunnan Observatories, and the University of Heidelberg, utilized high-precision data from the Gaia satellite to identify the OC groups. Their analysis focused on three-dimensional positions, velocities, and ages. G1 and G2 displayed distinctive ring-like and arc-like structures, indicative of external compression events.

In light of these patterns, the team used a triggered star formation model to construct spatial correlation maps between cluster age and distance from likely SN explosion sites around the regions where the OC groups originated. A clear correlation between age and distance supported the hypothesis that a sequence of SN explosions occurring over a brief period sequentially initiated the formation of G1 and G2.

A diagram showing the four new primordial OC groups (G1–G4) uses blue, green, red, and orange dots to represent each group respectively. Tangential velocity vectors for the member clusters are denoted by black arrows, with arrow lengths scaled in relation to a red reference arrow at the diagram’s upper right corner. (Credit: XAO)

To further assess their theory, the researchers conducted trajectory traceback analyses on 607 pulsars, which are remnants of SN events. Several of these pulsars had trajectories pointing to birthplaces that matched the expected SN explosion regions. This spatial alignment—along with observed gradients in cluster ages and the locations of SN remnants—reinforced the theory of feedback-driven, hierarchical formation of these OC groups.

The study underscores the significant role of feedback mechanisms like SN explosions in orchestrating large-scale star formation and influencing the dynamic development of star clusters in the galaxy. Additionally, it contributes valuable insights into identifying feedback signatures in galactic structure and offers a framework to connect star formation, stellar evolution, and feedback dynamics across various scales.