James Webb Telescope, closer to the first glimpse of the Universe

400, 350, 300, 220 … In the past two weeks, millions of years have passed, like so many sporting results of a summer competition. Last week, with fanfare, Works announced the observation of a galaxy that existed just 300 million years after the Big Bang. The record was broken on Wednesday, July 27 by an international team including French astrophysicists, with a galaxy estimated to date back 220 million years after the Big Bang.

This excitement is thanks to the James Webb Space Telescope JWST. The telescope, sent on December 25, 2021 with a delay of more than ten years, delivered its first images on July 11. “It was a big bet but the preliminary results are great, entrusts to François Hammer, specialist in the evolution of galaxies at the Paris Observatory. The very first image was captured in just 12 hours of exposure, compared to 240 hours for the Hubble predecessor. And it’s much more precise! »

A look at hundreds of galaxies

The released images have amazed the general public, like that of the Carina Nebula, where one would almost believe to see sand dunes under a starry sky, or the planetary nebula of the Austral Ring, a ring of blue tipped and orange. The most important of the photos for experts bears the unpoetic name “Smacs 0723”, a galaxy cluster in the constellation Flying Fish.

On a black background there are a multitude of white, blue and orange-red dots. “This view actually flattens several levels, describes David Elbaz, Director of Research in CEA Saclay’s Astrophysics Division. The very bright six-pointed dots represent stars, the closest. The rounder white dots are the galaxies of the observed cluster, and finally the red and orange dots far beyond are as many very distant galaxies. » If some of them appear completely distorted, the fault is with a so-called “gravitational lensing” light effect.

“The distant objects in the background send rays of light toward the telescope. Along the way, these rays hit the galaxy cluster. The gravity of this cluster warps space-time and warps light, deciphered the astrophysicist Jean-Pierre Luminet. Sometimes we even witness doublings, gravitational reflections. » This magnifying effect, which multiplies the background and the luminosity, allows the observation of very distant and faint galaxies.

Galaxies just after the Dark Ages of the Universe

However, it is not even this impressive view that hosts the record announced on Wednesday July 27th. The international CEERS team has unearthed the oldest galactic ancestor in other data collected by the James Webb telescope that has not been released to the public. This galaxy, nicknamed “Maisie,” would therefore date back as far as 220 million years after the Big Bang, or three times nothing on the scale of the age of the Universe – nearly 14 billion years.

“We’re going back to times when we weren’t even sure galaxies existed,” explains David Elbaz, member of the CEERS team. Fast rewind. First the big bang, then a few adventures and suddenly darkness. The universe has been going through a dark age since its 380,000th anniversary. “It became opaque before gravitationally lit up with the formation of the first stars and the first galaxies, vulgarizes François Hammer. Ideally, the James-Webb should tell us more about when the lamp lights up.»

The telescope can rely on its extra large mirror (read the markings) and its infrared instruments. “Light travels great distances to reach us, begins David Elbaz. The space expands like an accordion unfolding. So the light is also stretched, the wavelengths increase and we experience a redshift. »

James Webb Telescope, closer to the first glimpse of the Universe

Observation in the infrared then makes it possible to see this distant and very ancient light that has become invisible. “Infrared makes it possible to see colder and more distant objects,” says Jean-Pierre Luminet. The second benefit is that infrared can “penetrate” clouds of dust and gas, making it easier to observe the areas where stars are being born.

Analysis of the atmosphere of exoplanets

Another too-often-forgotten mission, the James-Webb, will also analyze in more detail the atmospheres of exoplanets, the planets outside the solar system. In addition to the first four images, the space agencies involved have also published the composition of the atmosphere of Wasp-96 b. The results show the presence of water molecules. Not enough to dig that much into possible life forms, because Wasp-86 b is a gaseous giant with the image of Jupiter, totally inhospitable.

“Water can be very present in the Universe and this is not sufficient evidence to prove the existence of life”, remembers Francois Hammer. The astrophysicist from the Paris Observatory urges caution in the face of overly thunderous announcements: “It’s a brand new telescope and there are some calibration issues. »

Refinement of our theories about the origin of the universe

On the CEERS page, David Elbaz easily sees that the age of the “Maisie” galaxy needs to be confirmed, and that by spectroscopy, not just observation. “These dates should arrive in December at best, he hopes. The probability of seeing a galaxy of this size in this region was zero. We are therefore wondering whether this is an exceptional case or a challenge. Are there more primordial galaxies in the JWST images than our models predict? »

James Webb Telescope, closer to the first glimpse of the Universe

“The standard cosmological model has difficulties in explaining the formation of galaxies very early in the universe, recognizes Jean-Pierre Luminet. Until a few years ago, it was believed that they formed at best a billion years after the Big Bang. » If James-Webb’s findings confirm the theories, the boundaries of our universe will only be better defined. And on the contrary, if this highlighting does not match, new models must be determined.

In any case, the scientific enthusiasm is not waning. About fifty studies are already available in pre-release, the pre-peer review phase, on the ArXiv platform. And every day brings its new batch. Who knows, maybe next week a new study will unveil an even more distant galaxy…


An extraordinary telescope

6.5 meters in diameter for the primary mirror that collects light from the universe, compared to 2.4 meters in diameter for the previous Hubble Space Telescope. It is the largest mirror ever deployed in space.

Four scientific instruments are on board the James-Webb, two of which are partly French (Miri and NIRSpec). These instruments allow observations in the infrared of the first galaxies and stars.

1.5 million kilometers separates the earth from the telescope located at Lagrange point 2. This distance, which prevents any repair, is necessary to scan the distant universe in the infrared.

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