The Universe and Its Large-Scale Structure

A useful hierarchy is: Stars → Galaxies → Groups → Clusters → Large-scale cosmic structures Large galaxy surveys show patterns including: galaxy groups; galaxy clusters; filaments; walls; voids. Together, these structures form what is often called the: cosmic web*. Long structures containing galaxies and matter.

Very large regions containing much less matter than surrounding structures.

Gravity plays a central role in the growth of cosmic structure. Small early differences in matter density could grow over cosmic time as gravity attracted more matter toward denser regions.

For gravitational attraction: **F = Gm₁m₂/r²** This is a simplified useful reminder of gravity's role; large-scale relativistic cosmology requires a more complete gravitational description.