Using the James Webb Space Telescope (JWST), an international team of astronomers has found compelling evidence that early galaxies were responsible for the reionization of the early universe. This is the process by which neutral hydrogen atoms are ionized, making the universe transparent to light at wavelengths that would have been absorbed by the atoms. The research was done by members of the EIGER collaboration, which is using the JWST’s Near Infrared Camera (NIRCam) to study light from quasars in the early universe.
Does someone smarter than me wanna ELI5?
After the big bang its believed there were huge clouds of hydrogen everywhere. Neutral hydrogen absorbs visual light frequencies.
This would mean we wouldn’t be able to see distant galaxies since there would be giant clouds of hydrogen everywhere blocking the view.
Obviously we can see distant galaxies, this is because we are surrounded by large ionised hydrogen clouds. Ionised hydrogen is transparent (e.g. doesn’t absorb) to light. So something must have ionised (give it an unequal number of positrons and electrons) the hydrogen clouds.
Quasars (black holes) emit huge amounts of xray and ultraviolet radiation. This kind of radiation would ionise hydrogen.
JWST was looking into the first billion years of the universes existence and found quasars, around these quasars is large amounts of ionised hydrogen.