The Primitive Universe Was Not Icy: A Discovery That Redefines Cosmic Origins

The story of the universe begins well before the first stars. Long perceived as a phase of cold and silent inertia, this initial period always intrigues cosmologists. The main stages such as recombination or the emergence of visible light have been patiently reconstructed, but other gray areas persist. Among them, the era of reionization remains a fragile border between conjecture and detection. But a new signal precisely turns this story.

At the origins, a black, dense and silent world

For hundreds of millions of years after the Big Bang, the universe looked like an abyss without light. Neither stars nor galaxies were yet born. Only immense neutral hydrogen tablecloths remained from the primitive chaos of the particles. At that time, astronomers speak of dark ages. Indeed, the light is trapped there and cannot cross the space freely. This step marks a transition where the universe is still invisible, although it is already in training.

This cosmic silence was preceded by a key step called recombination. At that time, protons and electrons formed stable atoms, allowing light to finally free itself. It is this fossil radiation that Cobe and WMAP satellites captured, revealing a frozen image of the cosmos about 380,000 years after the Big Bang. But between this recombination and the appearance of the first stars, an immense mystery remained. No direct signal so far allowed to know what had happened during this long wait.

The strange warming detected before the time of re -Réionization

To understand the stellar origins, the researchers targeted a very specific radio signal. This is the line at 21 centimeters, issued by neutral hydrogen. Thanks to its properties, this wave crosses the material without being absorbed. It therefore allows, by extension, to access clues on the first phases of the universe. At that time, visible light did not yet circulate freely, like the Raple Sciencealert.

Thanks to a decade of data from RadiTelescope Murchison Widefield Array, installed on Wajarri Yamaji land in Western Australia, scientists have pushed the limits of the observable. By extracting the parasitic noises caused by the earth's atmosphere, the nearby stars and even their own instrumentation, they have isolated a residual signal that changes the situation. As indicated by the project of the project led by Curtin University, the results suggest that intergalactic gas was already warmed around 800 million years after the Big Bang. This moderate temperature makes it impossible a scenario of reionization in an icy universe.

Observations, published in The Astrophysical Journal by CD Nunhokee and its colleagues, confirm that the lower limits measured by the power spectrum at 21 cm exclude the so -called “cold reionization” models. This necessarily involves a form of early energy intake.

Why this discovery changes our understanding of the primitive cosmos

The era of reionization, which extends about a billion years after the Big Bang, marks the transition to a transparent universe where the light of the stars and galaxies begins to propagate freely. Until then, it was assumed that this process had been engaged in a very low thermal environment, produced by the simple adiabatic cooling of cosmic expansion. But the study conducted by the International Center for Radio Astronomy Research shows that it is no longer tenable.

According to the radiostronome Cathryn Trott, the measures show a moderate but significant heating. It specifies that this phenomenon could be caused by X -rays from the first black holes or the remains of massive stars. This energy diffused in intergalactic gas would therefore have acted long before the visible light arose.

The effects are not limited to a simple change in temperature. Indeed, this early warming upsets existing models. He suggests that certain structures such as mini-quasars and emerging galaxies have influenced the space well before becoming visible. Thus, cosmologists now rethink the order of the main stages of the universe. In addition, the James Webb telescope could very soon refine this scenario. Thanks to its infrared capacity, it can capture the oldest lights, as NASA explains in its files.

Astronomers now have a new fundamental index. That of a warmed universe even before being illuminated. This thermal shade, almost imperceptible, however redraws the contours of our cosmic origins.