Numerical Simulation Study on the Origin of Stellar Snakes

Abstract

Thanks to recent advancements in observational technology, significant progress has been made in the search for open clusters. Among these, binary open clusters have become a key focus of cluster studies due to their unique properties and complex interactions. The open clusters NGC 2232 and Tian 2, which are located at a very close distance from each other, are considered a binary cluster system. Observations show that these two clusters have very young and similar ages (approximately 30–40 Myr). There is a structure formed by stars with a length exceeding 200 pc near the binary star cluster, which is called the “Stellar Snake”. Through a series of high-precision N-body dynamical simulations (N: the number of bodies), the formation of the stellar snake has been dynamically modeled. The simulation results indicate that the two clusters are currently in a non-dynamically bound state, and it remains uncertain whether they were bound at the time of their formation. If the system is initially considered unbound, the two clusters show no significant mass loss after independently evolving for 100 Myr, and their mass loss rate is not significantly higher than that of a single open cluster in the Milky Way under tidal stripping. In contrast, if the two clusters were initially bound at birth and evolved together for 100 Myr, the tidal effects from mutual orbital motion within this bound system significantly accelerated the mass loss of the clusters. As a result, the stripped stars formed a larger tidal structure, but the tidal stream did not effectively form a structure resembling the stellar snake with a span over 200 pc. Additionally, considering the observed stellar snake as a one-sided structure, it does not match the symmetric tidal arms and tails that would be expected from tidal interactions. Therefore, the stellar snake is not likely to be a product of tidal effects, but rather a formation mechanism more consistent with the collapse of primordial gas along a filamentary structure.