What you see in the picture is the WLM or Galaxy Wolf-Lundmark-Melotte, whose name is so complicated because it is called as who discovered it.
As you see it is a curious thing because it is a “big” star cluster surrounded among other normal distance. Think that you see at a distance (between them) are normal nearby stars while the cluster is the other galaxy.
The interesting thing about the WLM that is 3 million light years (more or less) is that it is the most distant galaxy of our galaxy cluster.
If cluster of galaxies because the universe is very large and galaxies, gravity, tend to gather, to not be alone. Therefore, galaxies are in small groups scattered throughout the universe.
The interesting thing about all this is that if we calculate the mass of each galaxy is not enough to keep them together, the total mass (approximate, if) is not enough to make them together. There must be “something else” and that something else is not seen, it is dark matter (or should be, of course).
That is, galaxies are held together in groups through “something”, a glue that unites them and also among various groups as well. Dark matter is the glue that binds the universe, both locally and in general.
There are “tubes” of dark matter that unite groups of galaxies maintaining consistency. In fact, if we look at the systems known galaxies with dark matter calculations between them (which are very few, remember) we see that have a known way, like a neural network. The so-called cosmic web (cosmic web), the other image.
Remember that the “visible” matter is only 5% of the amount of the universe, dark matter 27% and the rest (68%) dark energy. That is, there are more visible than visible universe.
I recommend, always, see this Wikipedia entry to open the mouth and, from there, look for more information (if you are interested, like me) these topics: https://en.wikipedia.org/wiki/Observable_universe
Will bootstraped the cosmic web? (This is a joke).