Mysterious force that cleared the cosmic fog at the dawn of the universe may not be what we thought

The mysterious force that cleared the cosmic fog at the dawn of the universe may not be what we thought, a new study suggests. The results hint that astronomers may need to rethink a major aspect of cosmological evolution, which led to the universe we clearly see today.

Around 400,000 years after the Big Bang, the fledgling universe finally cooled enough to form atoms — mostly hydrogen. But these neutral, non-electrically charged hydrogen atoms shrouded the cosmos in a fog that made it opaque to ultraviolet (UV) light.

Then, after the first stars flickered to life and gathered into galaxies, bursts of radiation ionized the neutral hydrogen. This turned the impenetrable fog of atoms into electrically charged protons and electrons, allowing light to pass through interstellar space unimpeded and, eventually, reach our observatories. This cosmic curtain parting is known as the Epoch of Reionization, or what a team of researchers studying it call the “last major phase transition in the universe.”

“We don’t know exactly what objects caused reionization or how it evolved,” Cody Carr, an astronomer who focuses on galaxy evolution at the University of Michigan and first author of a new study of the epoch, said in a statement. “We know that it took place, but we don’t have complete answers to those questions.”