Following recombination, the universe was neutral and opaque to radiation. As the first stars and galaxies formed, their radiation reionized hydrogen. This “cosmic dawn” made the universe transparent again. Observing this epoch reveals how early structures evolved. Reionization impacts galaxy formation and star formation rates. Telescopes like JWST aim to study these events.
It matters because reionization transformed the universe into the transparent cosmos we see.
It also informs how matter condensed into stars and galaxies.
The universe became transparent again due to early cosmic light.
National Aeronautics and Space Administration [nasa.gov]