Table of Contents
This is an old revision of the document!
2. Galactic age
The Cosmic Dark Ages
Following recombination, the universe was filled with neutral hydrogen and helium but lacked luminous objects. Gravity slowly pulled matter into denser clumps within a dark, expanding cosmos.
Cosmic Dawn (Reionization)
The first massive stars and protogalaxies ignited. Their intense ultraviolet radiation re-ionized the surrounding neutral hydrogen, ending the Dark Ages and making the universe transparent to ultraviolet light.
Hierarchical Merging
Small "pregalactic blobs" and dwarf galaxies collided and merged to build up larger galactic structures. This "bottom-up" process created the massive galaxies we see today, including the Milky Way's halo.
Rise of Supermassive Black Holes
Massive concentrations of matter collapsed in the centers of young galaxies to form black holes. The accretion of matter into these holes powered the first quasars, which shone with the brightness of a trillion suns.
Peak Quasar Epoch
The era of maximum activity for Active Galactic Nuclei (AGN; quasars). As galactic cores consumed their fuel supplies, this violent activity eventually subsided, leaving dormant supermassive black holes at the centers of most normal galaxies.
Large-Scale Structure Formation
Galaxies organized themselves into vast sheets, filaments, and clusters (such as the Local Group), separated by immense voids, creating the "frothy" bubble-like architecture of the cosmic web.
Birth of Population I Stars
Enrichment of the interstellar medium by earlier supernovae allowed the formation of metal-rich stars (Population I) in galactic disks. This marked the transition toward the Stellar Age and set the conditions for future planetary systems.