Changes in binding energy of interacting galaxies

A formula is derived that describes the fractional change in binding energy of a galaxy that is in an impulsive collision with another galaxy. The equation includes variables for the masses of the perturber and the perturbed galaxy, the relative velocity of the perturber at minimum separation, and dynamical radius. The expression is shown to be applicable to all cases of interpenetrating fast collisions of galaxies with equivalent radii. (C.C.S.)