James Webb observed the birth of galaxies at Cosmic Dawn

The James Webb Space Telescope has struck another blow. For the first time in the history of astronomy, researchers were able observe the birth of three galaxies born during the Cosmic Dawn, the pivotal period when the very first stars began to form and illuminate the cosmos. Aesthetically speaking, the images are far from spectacular; nothing to do with those that Euclid recently reported to us. But it is still a sensational discovery thanks to which the fabulous telescope brings us a little closer to the origins of our Universe.

We can say that these are the very first “direct” images of the formation of galaxies », Rejoices Kasper Elm Heintz, lead author of the study at the valuable Niels Bohr Institute, at the University of Copenhagen. “ The James Webb has already shown us very early galaxies at more advanced stages of their evolution, but here we are truly witnessing their birth, and by extension, the construction of the first star systems in the Universe “, he specifies.

Remnants of the Cosmic Dawn

In fact, these objects are 13.3 to 13.4 billion years old. They would therefore have been formed between 400 and 600 million years after the famous Big Bang, the cataclysmic explosion from which the first constituents of matter emerged. Right after this event, the Universe was just one vast primordial soup consisting exclusively of subatomic particles — quarks, gluons, and leptons, then protons and neutrons in a second step.

We had to wait almost 400,000 years for them to finally begin to recombine into atoms ofhydrogen, the main constituent of stars, then helium. But these vast cosmic furnaces did not immediately begin to form spontaneously. For tens of millions of years, all this material remained virtually inert, and space was plunged into total darkness.

A NASA rendering of the early Universe timeline. The Cosmic Dawn began a few hundred million years after the Big Bang, after a large ionization event that allowed light to travel throughout the cosmos. © NASA / STScI

To get out of this period, which astrophysicists soberly call “ the Dark Ages » of the Universe, we had to wait a few hundred million more years. According to current models, it was during this period that the cosmos began to undergo vast gravitational collapses. Under the influence of vast pockets of dark matter called halos, baryonic matter (the “ordinary” matter that makes up the atoms and objects we interact with every day) began to accumulate in the form of dense clusters that gave birth to the very first stars.

The light from these, and the subsequent formation of the first galaxies, then flooded the cosmos with high-energy photons. These particles had the effect ofionize all nearby neutral hydrogen, thus allowing the first lights to circulate freely. This event has ended the Dark Ages and launched a new era, that of the Cosmic Dawn. And it is precisely these vast clusters of still neutral and inert hydrogen that the Webb’s infrared sensors managed to capture for the first time.

James Webb conquering our origins

This is therefore a fairly exceptional observation which once again shows the telescope’s ability to approach the origins of the cosmos. Researchers hope to gain valuable information about the early universe, which will make it possible to refine the models describing these still mysterious periods of the Universe. Because at the moment, our understanding of the Dark Ages and the Cosmic Dawn is essentially based on a theoretical framework that is certainly quite solid, but which must imperatively be reinforced with concrete studies to continue to move forward.

One of the most fundamental questions that humans have always asked is that of our origins. Here, we provide some answers by showing when some of the first structures in the Universe were created », Explains Gabriel Brammer, co-author of the study. “ This is a process that we will explore more closely, until we are able to put together more pieces of this great puzzle “.


To achieve this, the troops of the Niels Bohr Institute do not intend to stop there. The university press release specifies that the team has already submitted a request to obtain a new appointment with James Webb. They will undoubtedly have to wait a while, knowing that the king of telescopes is extremely courted by astronomers. But these very good results will undoubtedly help them to assert their case with the Space Telescope Science Institute, which manages the allocation of observation time. We can therefore expect that new data on the beginnings of the cosmos will reach us in the relatively near future, to the delight of astronomers and space enthusiasts.

The text of the study is available here.



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