In this work I investigate the statistical properties of a huge catalog of closely interacting pairs of dark matter haloes , extracted from the Millennium Simulation database .
Only haloes that reach a minimum mass \geq 8.6 \times 10 ^ { 10 } M _ { \odot } h ^ { -1 } ( corresponding to 100 particles ) are considered .
Close pairs are selected if they come within a critical distance d _ { crit } .
I explore the effects of replacing d _ { crit } = 1 { Mpc } h ^ { -1 } \rightarrow 200 { kpc } h ^ { -1 } on the evolution of separations , lifetimes , total masses and mass ratios of these pairs .