Scientists have shown what the Universe looked like before the first stars appeared

Scientists have completed processing data collected over the past years by the Atacama Cosmology Telescope (ACT) in Chile. This telescope replaced the Planck space observatory, which was the first to create a map of the relic radiation of the Universe. The new images have increased the clarity of the distribution of plasma and gas in the “childhood” years of the Universe’s development – approximately 380 thousand years after the Big Bang.

Image source: ACT Collaboration

«“We’re seeing the ‘first steps’ of the universe toward the creation of the earliest stars and galaxies. And it’s not just light and dark — it’s high-resolution polarization of light,” explained ACT telescope director and Princeton University professor Suzanne Staggs.

Determining the polarization of the microwave background radiation allows us to study in great detail the distribution of ionized hydrogen and helium in the first minutes of the life of the Universe by cosmological standards. These substances later formed the first stars, and then galaxies. The information obtained also gives an idea of ​​the distribution of dark matter, which collected visible matter around its clumps and, in fact, contributed to the formation of everything we observe.

Separately, scientists emphasized the preservation of the so-called Hubble tension – a discrepancy in the measurement of the expansion rate of the Universe based on relic radiation (in the early Universe) and on observations of stars and galaxies today. This discrepancy has not disappeared, and the new ACT data in the relic microwave range generally correspond to the readings obtained earlier from Planck.

The Atacama Cosmology Telescope was built in 2007 on top of Cerro Toco in the Chilean Atacama Desert and completed its operations in 2022. The newly released data are from the last years of its observations, from 2017 to 2022. Analysis of the information obtained will last for many years, providing scientists with extensive material for new discoveries.