3D Graphics math: Bodies formed out of freely moving spheres

Right now I am watching Farbrausch's Magellan (my attention was specially drawn to the nebulous objects 1:06 - 2:01). How can I make these objects?

My first guess is that a set of spheres can be created. These spheres are liable to gravity and other physics effects. Yet they are not being rendered. Instead, 开发者_StackOverflowtotally new meshes (or just one) are being created for every frame to cover the union of the spheres. These meshes are being rendered instead of the spheres. Perhaps there be other effects... Are there any thoughts?

Have a look at metaballs and implementations (plenty of them online).