From a distance, the space object IC 2431, which is 681 million light-years away, may appear to be a monolithic, but slightly chaotic galaxy formation. But if we look at it more closely, using the capabilities of the Hubble Space Telescope for example, we can see that it is in fact not a single galaxy, but three different galaxies that are in the process of merging. Sometime in the distant future, these galaxies will completely merge into one large galaxy, which will nonetheless very long have the "scars" left by the collision now taking place.
The occurrence of galaxy collisions and mergers should be a fairly rare occurrence in the Universe. But given the vast number of galaxies, they are not so rare and they are an integral part of cosmic evolution processes on a galactic scale. Our galaxy, the Milky Way galaxy, for example, has by many accounts taken part in merger processes several times in its 13.6 billion years of existence.
Astronomers believe that all galaxies are gravitationally connected to each other, and thus they are located and move along the "threads" of an invisible cosmic global network, whereby they constantly collide, merge and form clusters that play a vital role in the evolution of the universe.
Galaxy collisions create gravitational disturbances that perturb and compress the clouds of gas contained within these galaxies. This is when galaxies, in whose depths the star-forming processes have all but died out, are "reborn", intensively forming whole "stellar maternity wards" in which young, hot stars are intensively nucleated and formed.
The most common type of galaxy collision and merger cases are those involving two "actors". Cases of three or more galaxies merging together at the same time are rarer, but they do occur. However, scientists cannot always distinguish between a triple-collision event and a usual double-collision event, especially in the latter phases of these processes.
In these latter stages, supermassive black holes located in the central regions of each galaxy become gravitationally interconnected and move in complex orbits around each other. Some of the black holes may be hidden from view by clouds of gas and dust, obscured by another black hole, etc., making it difficult to identify the number of galaxies involved in the original merger process.
Bound black holes left behind by the merger of several galaxies will, according to astronomical scientists, one day merge together to form one super-large and super-massive 'monster'. Such events should generate bursts of gravitational waves, but so far, scientists have not been able to register any such event. But this is not surprising given the rather short lifetime of gravitational sensors compared to the frequency of galaxy merger events, plus the signals may have frequencies lying outside the sensitivity range of existing gravitational wave sensors.
Nevertheless, each detected galaxy collision adds new data to our knowledge, and one day this will lead to the development of a true model of the processes taking place, which will allow us to predict events in the Universe for many millions and billions of years to come.