  Two mathematical models of three bodies of variable masses are used to obtain
a qualitative description of two interacting galaxies with mass exchange and
mass loss. The reference system is centred on the largest body (the most
massive galaxy), and the other two bodies are allowed to move around this one
under the laws of gravity. The third body, which simulated the mass lost by the
second galaxy in the form of a tail, increases its mass due to the mass lost by
the second body and follows its trajectory. We are interested in knowing the
time evolution of the separation of the two bulges of the interacting galaxies,
and the parameters for the analytical models are obtained by running
simulations with the GADGET-2 N-body code. The resulting behavior of this
distance in our mathematical models is qualitatively in good agreement with
that obtained by this code.
