This confusing scenario, which further analyzes will have to confirm, occurred between 500 and 700 million years only after the Big Bang that occurred 13.8 billion years ago.
Either in the very young Universe, therefore very distant.
The James-Webb Telescope (JWST), operational since July 2022, has been able to explore this little-known region thanks to its NIRCam instrument and its powerful vision in the infrared, a wavelength invisible to the human eye and whose observation allows you to go back a long way in the past.
He unearthed six galaxies much more massive than expected in this primordial Universe, reports a study published in Nature.
Two of them had already been pointed by the Hubble telescope, but had gone unnoticed as the light emitted was weak.
According to the interpretation of the new JWST images, these six galaxies - called "candidates" at this stage because the discovery will have to be confirmed by spectroscopic measurements - contain many more stars than expected.
One of them would contain up to 100 billion.
"It's about the size of the Milky Way, which is crazy," Ivo Labbé, first author of the study, told AFP.
It took our galaxy 13.8 billion years to form this quantity of stars, when this young galaxy would have done the same in just 700 million years "20 times faster", develops this researcher from the Swinburne University of Technology in Australia.
Such distant galaxies of this size have no place in the current cosmological model which attempts to understand the structure of the Universe.
"Theory tells us that at those early ages, galaxies are very small and grow very slowly. You would typically expect them to be 10 to 100 times smaller in terms of the amount of stars," he says. the astrophysicist.
"The Pattern Cracks"
Finding such big ones, "it's like jumping off a cliff" in his eyes.
What would go wrong?
The suspect could well be dark matter, the mysterious invisible matter that populates the Universe.
While scientists can't detect it, they know its behavior quite well and know that it plays a key role in galaxy formation.
"Dark matter must + fit together + to form a halo which attracts towards it the gas from which the stars will be born", deciphers Professor Labbé.
However, this "coagulation" process is supposed to take a long time.
It would therefore seem that "things have particularly accelerated" in this primordial Universe, which would have been "more efficient than we thought" in making stars, comments David Elbaz, astrophysicist at the Atomic Energy Commission (CEA ), who did not take part in the study.
This could be explained by the process of expansion of the Universe which is accelerating faster than we thought, notes this scientist involved in the telescope observation program developed by NASA.
The subject agitates the debate among cosmologists and this discovery is "all the more exciting as it is one more indication that the model is cracking", analyzes David Elbaz.
Europe's Euclid space telescope, due to be launched into orbit this summer in an attempt to unlock the secrets of dark matter, should help unravel the mystery, he points out.
Professor Labbé cites the black swan theory, according to which an unpredictable and improbable event, if it occurs, has a considerable impact.
"If only one of the six candidate galaxies is verified, the theory will have to be reviewed".
© 2023 AFP