A Windy Early Universe
The early universe was a vastly different place from the one we see today. No stars burned in faraway galaxies â€” there werenâ€™t any galaxies. Instead, photons were trapped in a dance with the hot plasma of protons and electrons that suffused the universe. Sound waves rang out across this primordial soup, sloshing gas and photons into waves of higher and lower density. Only after about 300,000 years did the universe expand and cool enough for protons and electrons to begin to combine into hydrogen atoms. That set the photons free to travel across the universe, giving us the cosmic microwave background.
Meanwhile, the hydrogen atoms fell together into gravity wells created by clumps of dark matter, starting the building process for proto-stars and proto-galaxies. But thereâ€™s a catch. The sound waves ringing through the dense primordial soup gave some hydrogen atoms a bulk motion. That created a â€œwindâ€ of ordinary matter that simply swept past the smaller of the dark matter clumps. The existence of that wind might have important consequences for the formation of structure in the early universe, researchers found in 2010. Now, an international team reports this week in the journal Nature the first simulated 3D maps that take this wind effect into account.