The Formation of Binary Star Clusters in the Milky Way and Large Magellanic Cloud

TL;DR

This study uses N-body simulations to explore how binary star clusters form and evolve in the Milky Way and Large Magellanic Cloud, revealing the influence of initial conditions and environment on their formation and longevity.

Contribution

It provides new insights into the formation mechanisms and dynamical evolution of binary star clusters through detailed simulation analysis.

Findings

Approximately 45% of stellar aggregates form binary clusters within 20 Myr in the Milky Way.

Around 90% of binary clusters in the LMC survive beyond 20 Myr.

Merging of binary clusters can produce fast rotating star clusters with flat rotation curves.

Abstract

Recent observations of young embedded clumpy clusters and statistical identifications of binary star clusters have provided new insights into the formation process and subsequent dynamical evolution of star clusters. The early dynamical evolution of clumpy stellar structures provides the conditions for the origin of binary star clusters. Here, we carry out $N$-body simulations in order to investigate the formation of binary star clusters in the Milky Way and in the Large Magellanic Cloud (LMC). We find that binary star clusters can form from stellar aggregates with a variety of initial conditions. For a given initial virial ratio, a higher degree of initial substructure results in a higher fraction of binary star clusters. The number of binary star clusters decreases over time due to merging or dissolution of the binary system. Typically, $\sim 45\%$ of the aggregates evolve into binary/multiple clusters within $t=20$~Myr in the Milky Way environment, while merely $\sim30\%$ survives beyond $t=50$~Myr, with separations $\lesssim 50$~pc. On the other hand, in the LMC, $\sim 90\%$ of the binary/multiple clusters survive beyond $t=20$~Myr and the fraction decreases to $\sim 80\%$ at $t=50$~Myr, with separations $\lesssim 35~$pc. Multiple clusters are also rapidly formed for highly-substructured and expanding clusters. The additional components tend to detach and the remaining binary star cluster merges. The merging process can produce fast rotating star clusters with mostly flat rotation curves that speed up in the outskirts.