In
physical cosmology,
galaxy filaments (subtypes:
supercluster complexes,
galaxy walls, and
galaxy sheets) are the largest known structures in the
universe. They are massive, thread-like formations, with a typical length of 50 to 80
megaparsecs h-1, (163 to 261 million light years) that form the boundaries between large
voids in the universe. Filaments consist of gravitationally bound
galaxies; parts where a large number of galaxies are very close to each other (in cosmic terms) are called
superclusters.