Statistical analysis of the probability of globular clusters interactions with each other and with the galactic centre according to Gaia DR2 data on the cosmological time scale

Abstract

The main idea of the work is to study the dynamic evolution of the orbits of globular clusters (GCs) lookback in time obtained from the cosmological models that are closest to the potential of the Galaxy. This allows us to estimate the probability of close passages ("collisions") of the GC with each other and with the Galactic central in the Galaxy that dynamically changed in the past. To reproduce the dynamics of the Galaxy in time, we used five from 54 potentials, which were selected from the large-scale cosmological database IllustrisTNG-100, and which in their characteristics (mass and size of disk and halo) are similar to the physical values of the Milky Way. In these potentials variable in time, we reproduced the orbital trajectories of 143 GC in 10 Gyr lookback in time using our own high-order N-body parallel dynamic code φ-GPU. Each GCs was treated as a single physical particle assigned the position and velocity of the GCs center from the Gaia DR2 observations. For each of the potentials, 1000 initial data were generated with randomized initial velocities for the GC within the observation data errors. We assumed that passages with a relative distance of less than 100 pc and a relative velocity of less than 250 km/s are close passages. Clusters passages at farther distances and/or with more high velocities do not have a significant dynamical effect on GCs orbits. In our opinion, more changes in GCs' orbits can be produced by clusters passages with low velocities and at distances less than (as an example, 4) several sums of half-mass radii. Therefore, we analyse such close passages aside (for short, such passages we name "collisions"). To identify clusters that had close passages with GC, we used the criteria of relative distance: it must be less than 100 pc. Applying these criteria, we obtained statistically significant rates of close passages of the GCs with each other and with the SMBH. We found that during their evolution, GCs have on average approximately 10 passages from each other and approximately 3-4 close passages of GCs near the Galactic central for 1 Gyr at a distance of 50 pc for each of the obtained potentials.