When discussing about galactic 'collisions' and mergers, such as the predicted future encounter between the Milky Way and Andromeda, it is often said that actual collisions among stars are extremely unlikely, it's just that the mutual gravitational influence of both galaxies on each other will gradually deform, distort, stretch or squeeze the galaxies' shapes, they will gradually engage in a gravitational dance around common centers of gravity, and slowly, if the gravitational attraction is strong enough to maintain the bond, the two structures will eventually evolve into some new shape as a new single and larger galaxy. Assuming that the galactic cores (say both include a super-massive black hole) are following paths far from heading to each other head-on, they will also enter a gravitational dance around a common center of gravity. And all the stars from both galaxies would get involved into a highly complex motion affected by the common center of gravity of both galactic centers, and possibly by each of them individually if they pass close enough to any of them. This could in principle last for billions of years before the two cores get closer and closer to each other and finally merge into a new single galactic core, combining the mass of the two previous cores. My question is, have we observed any such galaxies which display 2 separate cores resulting from a relatively recent merger? and if so, how do they look like? how they behave? what are their most interesting features? And in case we have not detected any such dual-core galaxies, what would explain that fact? Wouldn't it be natural to expect that such galaxies must be out there in the right environments? TX!