ESA ESO: Distant Galaxies Reveal The Clearing of the Cosmic Fog

This artist's impression shows galaxies at a time less than a billion years after the Big Bang, when the Universe was still partially filled with hydrogen fog that absorbed ultraviolet light.

New observations with the ESO Very Large Telescope are probing this important phase of the early Universe by studying the light from some of the most distant galaxies ever detected. Credit: ESO/M. Kornmesser.

Scientists have used ESO's Very Large Telescope to probe the early Universe at several different times as it was becoming transparent to ultraviolet light.

This brief but dramatic phase in cosmic history - known as reionisation - occurred around 13 billion years ago.

By carefully studying some of the most distant galaxies ever detected, the team has been able to establish a timeline for reionisation for the first time.

They have also demonstrated that this phase must have happened quicker than astronomers previously thought.

An international team of astronomers used the VLT as a time machine, to look back into the early Universe and observe several of the most distant galaxies ever detected.

They have been able to measure their distances accurately and find that we are seeing them as they were between 780 million and a billion years after the Big Bang.

The new observations have allowed astronomers to establish a timeline for what is known as the age of reionisation for the first time.

During this phase the fog of hydrogen gas in the early Universe was clearing, allowing ultraviolet light to pass unhindered for the first time.

The new results, which will appear in the Astrophysical Journal, build on a long and systematic search for distant galaxies that the team has carried out with the VLT over the last three years.

"Archaeologists can reconstruct a timeline of the past from the artifacts they find in different layers of soil.

Astronomers can go one better: we can look directly into the remote past and observe the faint light from different galaxies at different stages in cosmic evolution," explains Adriano Fontana, of INAF Rome Astronomical Observatory who led this project.

"The differences between the galaxies tell us about the changing conditions in the Universe over this important period, and how quickly these changes were occurring."