Kinematic characteristics of the Milky Way globular clusters based on Gaia DR2 data

TL;DR

This study uses Gaia DR2 data to analyze the orbital dynamics of Milky Way globular clusters, identifying potential past encounters and collisions through detailed orbit integration.

Contribution

It introduces a high-order phi-GRAPE code for orbit calculations and provides new insights into possible historical interactions among globular clusters.

Findings

Identified four pairs of globular clusters with potential past encounters within 5 Gyr.

Demonstrated the effectiveness of the phi-GRAPE code for orbital simulations.

Revealed possible collision events among specific globular cluster pairs.

Abstract

Using the data from Gaia (ESA) Data Release 2 we performed the orbital calculations of globular clusters (GCs) of the Milky Way. To explore possible close encounters (or collisions) between the GCs, using our own developed high-order phi-GRAPE code, we integrated backward and forward the orbits of 119 objects with reliable positions and proper motions. In calculations, we adopted a realistic axisymmetric Galactic potential (bulge + disk + halo). Using different impact conditions, we found four pairs of the six GCs that may have experienced an encounter within twice the sum of the half-mass radii (collisions) over the last 5Gyr: Terzan3 - NGC 6553, Terzan 3 - NGC 6218, Liller 1 - NGC 6522 and Djorg 2 - NGC 6553.