It was formed in the earliest ages of the Universe, just 320 million years after the Big Bang. The most distant galaxy ever detected has been observed by the James-Webb Space Telescope, according to two studies published Tuesday (April 4) in Nature Astronomy.

The more the galaxies are distant, and therefore young, the more they are difficult to detect as their light signal is weak. The first surveys of the James-Webb Telescope (JWST), in service since July 2022, had identified many “candidate” galaxies in the infrared, a wavelength invisible to the human eye and whose observation allows to go back far in the past.

Powerful infrared vision from its NIRCam imager, combined with spectroscopy observations that analyze light coming from an object to determine its chemical elements, has “unambiguously” confirmed the existence of four galaxies. All located towards the red end of the spectrum, therefore very far apart.

Their age: between 300 and 500 million years after the Big Bang (which occurred 13.8 billion years ago), detail these studies. The Universe was then only 2% of its current age, in its so-called reionization period: after a period called the dark ages, it kind of reignited and began to produce a lot of stars.

The most distant of the galaxies unearthed by the JWST, dubbed JADES-GS-z13-0, would have formed “320 million years after the Big Bang”, and its light is the most distant ever observed by astronomers, explained Stéphane Charlot, of the Institute of Astrophysics in Paris, one of the authors of the study.

“A technological tour de force”

The space telescope also confirmed the existence of the galaxy GN-z11, which it dated to 450 million years after the Big Bang, and whose presence the Hubble telescope had detected.

The four galaxies observed are very low in mass – around a hundred million solar masses, compared to, for example, 1,500 billion for the Milky Way. But these galaxies are “very active in star formation, in proportion to their mass”, explains the astrophysicist.

The formation of stars would take place “at about the same rate as [in] the Milky Way”, a “surprising speed so early in the Universe”, comments this CNRS researcher. Another lesson is that these galaxies are “very metal-poor”, a finding consistent with the standard model of cosmology: the closer you get to the origins, the less time stars have had to form these complex molecules.

The JWST observation is “a technological tour de force,” said Pieter van Dokkum, an astronomer at Yale University of the United States, in a comment attached to the study. The telescope “almost every month pushes back the frontiers of exploration”, always going further into the Universe, he points out.

Last February, the instrument developed by NASA observed a population of six galaxies between 500 and 700 million years after the Big Bang, which seem much more massive than expected. If the existence of these galaxies were confirmed by spectroscopy, it could call into question part of the theory on the formation of the Universe.