The James Webb Space Telescope (JWST), the most powerful space observatory ever designed by humanity, continues to help researchers push the boundaries of the discipline – and it has just done so again in spectacular fashion. On Tuesday, May 27, an international team involving the Institut d'Astrophysique de Paris, an institution affiliated with the Sorbonne University and the CNRS, revealed a sensational image: it is quite simply the deepest image of the Universe to date.
This image is centered around Abell S1063, a galaxy cluster of monstrous proportions. But it's not this veritable behemoth, located about 4.5 billion light-years away in the constellation of Grus, that interests astrophysicists. The telescope's operators have instead used it as a tool.
Some objects, like Abell S1063, are so massive that they significantly distort the space-time around them. This phenomenon has a host of diverse consequences, but one that's particularly useful in this context: the path of light from background objects is forced to precisely follow this curvature. It can therefore be compared to a gigantic lens, which can be used to observe objects located at astonishing distances – provided that they are located very precisely on the same axis.
This is called gravitational lensing, and this is precisely what makes Abell S1063 so valuable in this context. Thanks to its enormous mass, the cluster can amplify the light from other, even more distant celestial bodies located behind it. They then appear as arcs, and these are the objects that really interest astronomers. Even if they are distorted, they are signals coming directly from the most distant regions of the cosmos. But in astronomy, looking far away also means going back in time; The more distant objects we observe, the closer we get to the origins of our Universe, with all that this implies in terms of scientific progress.
A journey to the origins of the Universe
The venerable Hubble has already taken part in this exercise several times. In 2016, he captured a beautiful image where several usable arcs could already be seen, corresponding to extremely distant galaxies – a precious resource for astronomers.
But since then, astronomy has moved into a new dimension thanks to the arrival of the JWST and its array of ultra-sensitive sensors. Specialists were therefore eagerly awaiting the opportunity to replicate Hubble's observation with this incredible piece of technology, and that's precisely what the team behind this work did. They trained their new favorite on Abell S1063 for over 120 hours to collect as much light as possible, and the result is simply breathtaking.
Thanks to its NIRCam, Webb managed to capture dozens of particularly bright and sharp arcs, corresponding to exceptionally old objects. According to the CNRS, these are tiny galaxies that appeared only 250 million years after the Big Bang – an absolute record.
For reference, this corresponds to what astronomers call the Dark Ages of the Universe, a kind of cosmic prehistory where the first stars were just beginning to illuminate a still young and almost opaque Universe. "These objects could be the direct ancestors of more developed galaxies, observed a few hundred million years later by the James Webb telescope," the institution explains in its press release.
The first Population III stars?
Among all these galaxies, there is one in particular that could well lead to a small astronomical revolution. The object in question, named GLIMPSE-16043, is indeed suspected of containing singular stars, known as “population III stars”.
This term refers to stars that were formed solely from primordial hydrogen and helium from the Big Bang, without any heavier elements. This would therefore be the very first generation of stars to have emerged at the dawn of the Universe. They would have played a key role in the great ionization event that allowed light to travel through the cosmos. Subsequently, they would have initiated the production of all the other elements necessary for the formation of modern celestial bodies – and by extension, the appearance of life. Suffice it to say that if the presence of population III stars were confirmed, it would be a major scientific breakthrough.
But beware of jumping to conclusions. To date, these population III stars remain hypothetical;their existence has never been directly confirmed. And these images alone do not yet allow us to verify this hypothesis. To decide, additional observations based on spectroscopy, a technique that allows us to determine the chemical composition of an object using its light spectrum, will be needed.
The good news is that the team behind this work intends to repeat the work in the near future. It plans to launch a major spectroscopic observation campaign starting in July 2025. If everything goes according to plan, the long-awaited confirmation could come a few months later, once astronomers have had time to rigorously analyze the data. We look forward to seeing you again very soon, hoping that this immense potential will materialize.
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