Mergers, tidal interactions, and mass exchange in a population of disc
  globular clusters
  We present the results of a self-consistent $N$-body simulation following the
evolution of a primordial population of thick disc globular clusters (GCs). We
study how the internal properties of such clusters evolve under the action of
mutual interactions, while they orbit a Milky Way-like galaxy. For the first
time, through analytical and numerical considerations, we find that physical
encounters between disc GCs are a crucial factor that contributed to the shape
of the current properties of the Galactic GC system. Close passages or motion
on similar orbits may indeed have a significant impact on the internal
structure of clusters, producing multiple gravitationally bound sub-populations
through the exchange of mass and even mergers. Our model produces two major
mergers and a few small mass exchanges between pairs of GCs. Two of our GCs
accrete stars from two companions, ending up with three internal
sub-populations. We propose these early interactions and mergers between thick
disc GCs with slightly different initial chemical compositions as a possible
explanation for the presence of the spreads in metallicity observed in some of
the massive Milky Ways GCs.
