What are the largest objects in the Universe? Not the planets, big as they are, nor the star they orbit, nor any star. Collections of stars, Galaxies, are the largest independent visible objects, but collections of Galaxies are by definition larger. A group of gravitationally bound galaxies is known as a cluster of galaxies. The Local Group contains our galaxy, the Andromeda galaxy and a few dozen smaller ones. Clusters of clusters of galaxies are called Superclusters and are the largest gravitationally bound objects in the universe. Our supercluster is called the Virgo supercluster as its central member is the Virgo cluster, so called as it can be found mostly in the constellation of Virgo as seen from Earth.
So where am I going with this?
Nasa has released a composite picture of work done in many wavelengths (Using Hubble – UV and optical – and the X-ray space telescope Chandra as well as the Earth bound Keck telescope – IR and optical) showing off a collision of several clusters. A supercluster known as a filament, as it is long and thin, has run through an area with a high density of galaxies, causing many collisions. It is still going and will cause further collisions.
The picture can be seen here.