First evidence of a collision between two unrelated open clusters in the Milky Way

A.E. PIATTI, K. MALHAN

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2022

0035-8711

We report the first evidence of an on-going collision between two star clusters inour Galaxy, namely IC 4665 and Collinder 350. These are open clusters located at adistance of ∼ 330 pc from the Sun and ∼100 pc above the Galactic plane, and they bothhave prograde motions with only a small difference in their velocities (Collinder 350moves ∼ 5 km s −1 faster than IC 4665); as inferred from ESA/Gaia based catalogue.Interestingly, the two clusters are physically separated by only ∼36 pc in space; adistance that is smaller than the sum of their respective radii. Furthermore, the clustersexhibit signatures of elongated stellar density distributions, and we also detect an onsetof an inter-cluster stellar bridge. Moreover, the orbit analysis suggests that the youngercluster IC 4665 (age=53 Myr) must have formed at a distance > 500 pc away fromCollinder 350 (age=617 Myr). These findings together imply that the two clusters donot represent merging of two objects in a binary system, rather, what we are witnessingis an actual collision between two independently formed star clusters. This collisionphenomenon provides a unique opportunity to explore new aspects of formation andevolution theory of star clusters.