Asymmetry in energy transfer in a collision of galaxies

Abstract

The time dependence of binding and translational energies of a pair of galaxies during head-on collisions has been studied with impulsive approximation. The two galaxies are assumed to be identical with mass distribution represented by that of a polytrope of index n=4. The results indicate that more than 80 per cent of the increment in the binding energy takes place when the centres of the two galaxies are separated by a distance less than three times the median radius of a galaxy. The change in the binding energy is asymmetric with respect to the distance of closest approach, the increment in the second half of the collisions being about double that of the first half.