Question: What is the largest object in the universe

Monique Henson answered on 16 Nov 2015:

It depends who you ask! It depends how you define object. If you define object as something that looks like a structure, then you might say the cosmic web. On really large scales the distribution of matter (stuff like stars, galaxies and dark matter) looks a bit like this. This web-like structure is called the cosmic web.

Other people would define an object as something that’s bound together by a force. For example, atoms and molecules (which make up all of the stuff around us that we can see) are bound by the electromagnetic force. When we look at objects in astronomy, they tend to be bound by gravity. The largest objects that we know are gravitationally bound are galaxy clusters. They are collections of hundreds of galaxies (each of which contains hundreds of millions of stars) all held together by gravity. You can see a couple of photos of some here and here.

However, not that long ago, some scientists thought they’d found something even bigger that is bound – the Laniakea Supercluster. A supercluster is a group of clusters. The Laniakea supercluster isn’t the first supercluster that’s been found, but it’s the first one where there’s strong evidence that it’s gravitationally bound. Scientists tracked the motion of the galaxies in the supercluster and used it to show that gravity was hold it all together in a stable state. There’s a great video (with a beautiful picture) explaining it here.