Seen by James-Webb, this galaxy puts us on the trail of the first stars in the Universe
GS-NDG 9422, a galaxy in the early Universe whose stars must be excessively hot…NIRCAM (infrared) © GOODS/Nasa/ESA
GS-9422: its name is not very pretty, but this galaxy could be a landmark. In any case, it is not like the others and is much talked about. Indeed, it is not its stars that shine the brightest, but its gas, which is an unusual characteristic. It is located in the Universe less than a billion years old (z=5.9), where the James Webb telescope discovers so many nuggets and mysteries.
To explain this exceptional luminosity of the nebulae it hosts, there is only one truly coherent solution: at the moment we see it, this galaxy forms a lot of stars and its stars are abnormally hot.
Population III stars formed the first heavy elements in the Universe
Finding the first generation of stars is an ancient quest, but one that has only recently become accessible to our technology. They are the ones who have forged the first heavy elements of the Universe (carbon, oxygen, etc.), called “metals” in astrophysics. They did not exist at the beginning of the Big Bang, when only hydrogen and helium gases surrounded space. Then the primitive stars were formed, never before seen, colossal, about 1000 or 10,000 times the mass of the Sun and devoid of these metals. In their core, they synthesized the first of them, then very quickly exploded in supernova. They are called population stars III as opposed to today's, like the Sun, of population I. Astrophysicists track them.
Astrophysical origin of the elements of the period table, therefore of the matter of the Universe © Nasa
This galaxy GS-9422 seems to be able to constitute the link between our current galaxies and the first ones that saw the birth of these primitive stars, because to make its gas shine so brightly, the stars that are there must have a temperature of about 80,000 °C, double what is expected for the most massive and hottest current stars. However, those of GS-9422 are not devoid of “metals”; they do not therefore belong exactly to the primitive generation and they seem to be between the two. The strange galaxy would thus be in a transition phase.
What really put astrophysicists on this trail was the light spectrum of GS-9422, which was nearly identical to the pattern predicted for a glowing environment of only nebulae lit by intensely hot stars.
Bottom panel: Predicted spectrum of a galaxy illuminated by its nebulae (yellow line) compared to the typical spectrum of a galaxy illuminated by its stars (white line). Top panel shows the actual spectrum of GS-0422, very similar to the predicted spectrum. © NASA, ESA, CSA, Leah Hustak (STScI)
The sensitivity of the James Webb Space Telescope is taking us places we have never been before, uncovering the mysteries that make up the Universe, exactly what it was designed to do. The marvelous and gigantic Population III stars better watch out, we are probably not far from lifting the veil on their original glow.
