Cosmic Structure Formation

Dark matter plays the starring role in structure formation — the process by which the smooth early universe became the lumpy web of galaxies, clusters, and voids we see today. After the Big Bang, dark matter clumps formed first, because dark matter is not slowed by radiation pressure the way ordinary matter is.

These dark matter clumps acted as gravitational seeds, pulling in ordinary matter that eventually formed stars and galaxies. Computer simulations like IllustrisTNG reproduce the observed cosmic web structure only when dark matter is included.