But they weren't. Instead, there were a few galaxies, but not enough to account for the high opacity. Becker thinks this is because this area might have been going through a particularly fascinating period in the Universe's history. After the Big Bang exploded and sent hot material streaming outwards, everything cooled off, including hydrogen, one of the brand-new elements. This hydrogen gas stayed neutral and uncharged until galaxies started to form, at which point some of the hydrogen started getting all charged up again, becoming "reionized" as light from the forming galaxies interacted with the gas. While ionized hydrogen is mostly transparent, neutral hydrogen tends to be more opaque to some ultraviolet wavelengths.