Has James-Webb just discovered the very first galaxies after the Big Bang?
Illustration of a zoom on a galaxy at very high redshift in the Universe, only 200 million years old. The box shows the five candidate galaxies seen by the JWST in infrared. © Generated by Brice Haziza on Bing Creator / Kokorev et al. 2024
If it is confirmed, which seems not to raise much doubt, this announcement will cause a lot of noise. The James-Webb Space Telescope (JWST) actually has almost no limits, an international team of around thirty researchers has just published the possible discovery of the oldest galaxies ever imaged. These five galaxies would have been born in the Universe which was only 200 million years old, or 70 times younger than today. Simply incredible.
We've never been this far in the past
The five oldest galaxies ever seen are in this infrared survey of the sky. © Kokorev et al, 2024
What's even crazier is that we are reaching the theoretical thresholds for the formation of the first post-war stars and galaxies.Big Bang. Starting to observe them is therefore an incredible achievement, because according to our current cosmological models, the very first galaxies were formed no earlier than 100 or 200 million years after the Big Bang. Surprisingly, we still aren't sure whether stars formed first or galaxies formed first, both initially being huge clouds of hydrogen and helium gas. Clearly, we will probably not find many galaxies older than those identified by James-Webb.
James-Webb pierces the barriers of time
The JWST therefore manages to do exactly what it was designed to do, namely to break through the technical barriers which until now prevented us from comparing our theories to observations. To produce beautiful astrophysical science in the clear and lift the veil on the mysteries of our origins. Let's talk a little about these five galaxies.
This is the GLIMPSE survey in the southern constellation Grue. These primitive galaxies have a red shift ranging from 15.9 to 18.6, which explodes the previous record of JADES-GSz-14, including the red shift (redshift in English) was 14.2.
The red shift is an effect due to the expansion of the Universe : light – its wavelength to be precise – lengthens, stretches over great distances, because the Universe itself grows and stretches. Measuring this shift therefore gives the distance from the object that emitted the light. This principle is similar to the sound of a police vehicle siren that gets louder and louder as it moves away from you…
Illustration of the red shift: the light emitted by the blue star stretches into redder wavelengths. It is perceived as red when it was blue. © Brews Ohare
Identifying such galaxies so far away required a helping hand from cosmic nature: the presence of the Abell S1063 galaxy cluster between Earth and the five so distant galaxies. This then acts like a magnifying glass, what we call the gravitational lens effect which amplifies the distant light coming from behind.
Here is a Hubble photo of the galaxy cluster Abell S1063.
AbellS1063 makes it possible to amplify the background light emitted by the candidate galaxies seen by the JWST. © NASA/ESA/HST
What are the implications for our understanding of the Universe?
As a member of the research team explains to the Space.com newspaper, “it remains very difficult to estimate the exact age of these galaxies and determine when they formed, but we are certainly approaching the first generation of galaxies […] Ultimately, these observations will place tight constraints on the physical processes that are allowed in our models of the Universe.”
Cosmology is living among its finest hours. We are getting closer and closer to the Big Bang barrier. And as the Latins said: “Felix qui potuit rerum cognoscere causas.” Happy is he who can touch the secret depths of things…
