No, those aren't just "clusters", they are completely different universes, and we can see them only because they emit electromagnetic radiation at frequencies commonly found in our own universe.
There are gaps out there where we can't see the adjacent universes because they do not emit electromagnetic radiation at frequencies we can detect, or even care about.
We can, however, sense their gravity.
This sort of stuff makes my mind melt. Which is why I studied the other side of the spectrum in sub-atomic particles. It was friendly, and possessed the unknown, but there weren’t these things that turned your mind into applesauce.