How did protogalaxies form after the early universe cooled?

After the early universe cooled sufficiently for matter to exist as neutral atoms, structure began to emerge from pre-existing density fluctuations. Small clouds of matter, known as protogalaxies, condensed from the expanding material and collapsed under their own gravitational fields to eventually form galaxies.1

Computer simulations suggest that the universe developed as a network-like arrangement of material, with matter gradually condensing where the strands of this network intersected. While 20th-century theories debated whether galaxies formed through the collapse of large gas clouds ("top-down") or the merger of smaller entities ("bottom-up"), modern understanding emphasizes that galaxies grow through continuous collisions and accretion.1

In the early universe, this process involved small, irregular building blocks that merged to form larger structures. Dark matter played a critical role in this evolution, providing the necessary gravitational influence to facilitate the formation and structure of these systems. The final shape of a galaxy—whether spiral or elliptical—was largely determined by the angular momentum of the original clouds during their collapse.12