Astronomers have found when and how the cosmic fog was lifted

Take a look at the image displayed here [click to redshiftenate]. Every object you see there is a galaxy, a collection of billions of stars. See that one smack dab in the middle, the little red dot? The light we see from that galaxy traveled for 12.9 billion years before reaching the ESO's Very Large Telescope in Chile. And when astronomers analyzed the light from it, and from a handful of other, similarly distant galaxies, they were able to pin down the timing of a pivotal event in the early Universe: when the cosmic fog cleared, and the Universe became transparent. This event is called reionization, when radiation pouring out of very young galaxies flooded the Universe and stripped electrons off of their parent hydrogen atoms. An atom like this is said to be ionized. Before this time, the hydrogen gas was neutral: every proton had an electron around it. After this: zap. Ionized. This moment for the Universe was important because it changed how light flowed through space, which affects how we see it. The critical finding here is that reionization happened about 13 billion years ago, and took less time than previously thought, about 200 million years. Not only that, the culprit behind reionization may have been found: massive stars. OK, those are the bullet points. Now let me explain in a little more detail.