This a really interesting read.
The Milky Way is part of a large structure called the Laniakea Supercluster which is 250 million light years across!
Chuckle, remember this sentence.
When I give public lectures, I always get a strange satisfaction out of telling the audience that galaxies don't exist!
go on to explain that, like a city which is a collection of stuff, galaxies are collections of things bound together under the force of gravity. A typical galaxy is simply a collection of stars, nebulae, clusters, planets, comets and so on, take them away and a galaxy won't exist!
Superclusters are largely the same, just a collection of galaxies bound together (well, not completely) under the force of gravity.
Superclusters like Laniakea and Einasto (which is 3 billion light years away) are among the largest structures in the Universe.
When we talk about clusters here on CN, we usualy are talking about a star cluster where I don't really remember seeing any galaxies. But in the defination provided above, a galaxy really is a cluster. It has groups of things. Which is all that a cluster really is. So, it is just one big old cluster.
Dan
