Finally , the epoch of structure formation began , when matter started to aggregate into the first stars and quasars , and ultimately galaxies , clusters of galaxies and superclusters formed .
With the formation of neutral hydrogen , the cosmic microwave background was emitted .
The epoch of structure formation began , when matter started to aggregate into the first stars and quasars , and ultimately galaxies , clusters of galaxies and superclusters formed .
With the formation of neutral hydrogen , the cosmic microwave background was emitted .