dark age

In cosmology, the dark age is the time between recombination when ions and electrons formed neutral hydrogen atoms, (around 380,000 years after the Big Bang or a redshift of 1090) and the epoch of reionization when hydrogen atoms once again split in large numbers, 150 million years after the Big Bang or some time between redshift 6 and 20. During this time, atoms were neutral and space was transparent but there were few light sources (i.e., stars) as yet, thus all was relatively dark. The era when the first stars formed is sometimes called the cosmic dawn.