One of the cosmology news stories from earlier this month involved data from the South Pole Telescope which helped show that the period of reionisation – which is when galaxies first began to form – happened over a shorter timespan than previously thought. They found that it was complete as early as 750 million years after the big bang:
The data provide new constraints on the universe’s first era of galaxy formation, called the Epoch of Reionization. Most astronomers think that early stars came to life in massive gas clouds, generating the first galaxies. The energetic light pumped out by these stars is thought to have ionized the hydrogen gas in and around the galaxies, creating “ionization bubbles” millions of light years across that left a lasting, telltale signature in the cosmic background radiation (CMB). This relic light from the early universe is visible today everywhere in the sky and was first mapped by UC Berkeley physicist and Nobel laureate George Smoot, founder of the BCCP.
“We find that the Epoch of Reionization lasted less than 500 million years and began when the universe was at least 250 million years old,” Zahn said. “Before this measurement, scientists believed that reionization lasted 750 million years or longer, and had no evidence as to when reionization began.”