Oldest galaxies and the re-ionization period

https://gizmodo.com/the-universes-oldest-galaxies-could-be-right-in-the-mil-1828390203

Citando:
"Atoms started forming from protons and electrons a few hundred thousand years after the Big Bang. The resulting gas cooled, creating stars, but the stars didn’t last long. They exploded in huge supernovae, sending energy out into space. This split the atoms back up once again, “re-ionizing” them. It’s unclear when the first stars started to form or when re-ionization started, but they’re important periods in the Universe’s history, because they set the ball rolling to create the galaxies we see today."

The most widely accepted model says that galaxies are actually visible gas and dust coalescing inside larger haloes of a yet-to-be explained kind of mass called dark matter. Galaxies began forming with the first stars, but during the re-ionization period, astronomers think that temperatures rose too high, halting further galactic growth. Only at some later period, when large-enough dark matter halos coalesced, would the galaxy formation process pick up again."