James Webb has (already!) observed the most distant galaxy known to date.

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NASA’s Space Telescope has been making discoveries since its official commissioning on July 12. After wowing the world with incredible images of distant galaxies and the deepest image of the universe to date, it now shows the oldest galaxy ever observed. The data indicate that it appeared 300 million years after the Big Bang.

The first hundreds of millions of years of the existence of the Universe (corresponding to a redshift, or a redshift greater than 10) mark an unknown and mysterious time. So far, only one galaxy has been detected at this distance: the galaxy GN-z11, discovered in 2016 thanks to data from Hubble and Spitzer. Its redshift was already especially high (z ≈ 11). The team set out to search for new galaxies from the same era, or even earlier, using James Webb’s NIRCam.

In a peer-reviewed preprint, scientists report the discovery of two “especially bright” candidate galaxies, named GLASS-z13 and GLASS-z11 (at redshifts 13 and 11, respectively). Although it seems to us that it was about 300 million years “only” after the Big Bang, GLASS-z13 becomes the most distant galaxy ever observed. The telescope observes only in the infrared range, but the data was “translated” into the visible spectrum: the galaxy has a round shape, almost red, but white in the center.

Look far to see the past

“We are potentially looking at the most distant starlight anyone has ever seen,” Rohan Naidu, an astronomer at the Harvard Center for Astrophysics and the paper’s first author, told AFP. Indeed, just as we see our Sun as it was eight minutes ago (because its light takes about eight minutes to reach us), light from the GLASS-z13 galaxy has been emitting for 13.5 billion years.

Galaxy GLASS-z13 in its stellar context. © Gabriel Brammer/Cosmic Dawn Center/Niels Bohr Institute/University of Copenhagen/AFP

Observing the formation of the very first galaxies after the Big Bang (13.8 billion years ago) is one of the main tasks of James Webb. We don’t yet know exactly when or how the earliest galaxies formed, and new data from the instrument will no doubt provide some answers.

This is only preliminary data, but scientists can already deduce some characteristics, some of which, to put it mildly, are surprising. For starters, the two discovered galaxies are particularly massive: they already accumulated about a billion solar masses in the form of stars within 300 to 400 million years after the Big Bang, according to the team. This suggests that stars formed much earlier in the early universe and faster than scientists thought.

The team also points out that the luminosity of these galaxies (with an estimated absolute magnitude in the ultraviolet range of -21) represents a “unique opportunity for detailed spectroscopic and morphological monitoring” at this distance. The modeling of their morphology suggests that they are both disc-shaped. In particular, the nearest galaxy, GLASS-z11, shows a light profile that proves that its galactic disk was already firmly in place at z ≈ 11.

New restrictions on the evolution of primitive galaxies

These galaxies appear to be relatively small: around 1600 light-years in diameter for GLASS-z13 and around 2300 light-years for GLASS-z11 (recall that our Milky Way is between 100,000 and 200,000 light-years in diameter). The researchers note that such sizes are typical for bright galaxies, usually observed at redshifts from 6 to 9.

“These two objects already impose new restrictions on the evolution of galaxies at the moment of cosmic dawn,” the authors of the study summarize. Their discovery is probably not a coincidence, they say, adding that there is probably a whole population of ultraviolet light sources at this distance with similar star-forming abilities.

If GLASS-Z13 really existed at the dawn of the universe, its exact age remains unknown at this point. It could have appeared at any time during the first 300 million years. This discovery, of course, has yet to be confirmed, but another group of astronomers, led by Marco Castellano of the National Institute of Astrophysics in Rome, who worked with the same data, came to similar conclusions, which gives Naidoo and his collaborators full confidence.

If these galaxies are confirmed by spectroscopy, and indeed two candidate galaxies with redshifts of 11 to 13 are yet to be discovered in every tiny part of the extragalactic field (about 50 arc minutes2), “it is clear that the JWST will succeed in pushing the cosmic boundaries. on the brink of the Big Bang,” the researchers conclude.

R. Naidoo et al., arXiv.

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