This simulation of the Cosmic Dawn hides the JWST’s future secret target

Researchers have managed to model the first lights of the early universe with stunning precision in work described as a “monumental breakthrough”.

Billions of years ago, the Big Bang ignited our universe. This immense cosmic cataclysm has turned our world into a rapidly expanding bubble of superheated gas; in the space of a few nanoseconds, it gave birth to a gigantic bubble of gas in rapid expansion, and superheated to more than 100 billion billion degrees Celsius.

But that was just the start of a long chain reaction. After this colossal detonation, the Universe did not immediately take the shape we know today. To generate all matter, starting with the atoms that make up the current celestial bodies, he had to go through a period sometimes referred to as “Dark Ages”.

And there was light

This corresponds to a long cooling phase which lasted several hundred million years; at that time, the Universe was completely black, since the stars capable of illuminating it had not yet formed. And since this theory took shape, many astronomers and physicists have been trying to figure out how the universe was able to come out of this torpor.

Subsequently, gigantic clouds of gas ended up being compressed under the effect of the gravitational forces involved; at certain points, this pressure proved intense enough to set it on fire, thus giving rise to the first generation of stars.

But from that moment, whose age is estimated at 13 billion years, these ancient stars played a decisive role in the sequence of events through a process known as “reinonization”. The first stars irradiated their surroundings to the point to ionize all surrounding material; this means that they stripped the electrical charges from the atoms, thus giving rise to a vast particle-based cosmic mess.

This had a very concrete consequence; the hydrogen atoms, more or less ubiquitous at the time, were then transformed into ions positively charged. This is an absolutely decisive step; it inherited the very poetic nickname of “Cosmic dawn” in the scientific literature, because it is this ionization which has allowed light to travel to the four corners of the universe.

A colossal computer model

But this scenario and its modalities remain debated in the scientific sphere; today, it is still very difficult to say anything with certainty when working on events so distant in time. To study this critical transition, as is often the case in this discipline, researchers rely on computer simulations.

The problem is that these are extremely complex, by the researchers’ own admission. Indeed, reionization involves interactions “immensely chaotic and complex”, between various and varied actors such as gravity, gases, and radiation – including light. To simulate it correctly, it is therefore necessary to model these delicate relationships at phenomenal scales and time spans.

For these reasons, there are only a handful of labs in the world that have the hardware to perform simulations of this magnitude. “Most astronomers do not have access to a laboratory in which to conduct such experiments. Time and space scales are too large”, explains Rahul Kannan, an astrophysicist affiliated with the University of Cambridge.

And precisely, the prestigious university is one of the few institutions that have both the equipment and the brains necessary to carry out this kind of major project. This is what Kannan and his colleagues sought to do.

To achieve this, they tried to combine three elements thanks to the SuperMUC-NG supercomputer. A colossal machine which was not too much; the researchers estimate that this work could have taken … more 3500 years to a standard computer. A figure that illustrates the complexity of the problem.

Armed with this computational behemoth, the team began by combining a simulation of cosmic dust with the best current model of galaxy formation. They then introduced a “new algorithm” that “tracks how light interacts with gases”.

A compendium of billions of years of cosmology

And it was apparently the right recipe; they succeeded in producing a model dubbed Thesan, after the Etruscan goddess of dawn. This is the first coherent and large-scale simulation of reionization; it represents the cosmic events occurring in an area of 300 million light years for a long time several billion years. The first lights of the Universe have never been so close!

Thanks to Thesan, researchers were able to visualize the interactions of the early universe with an unprecedented level of detail, completely unseen to date. A golden opportunity to unearth fascinating details about the properties of the world at that time. In particular, they were able to dwell on the progressive illumination of this ebony black universe.

It’s like water in an ice cube tray”, explains Aaron Smith, co-author of the study. “It takes time, but after a while the edges freeze and the ice cream works its way to the center”, he explains. “It was the same in the early universe. It was a dark, neutral cosmos that ionized and illuminated when light began to emerge from the first galaxies”.

A tool at the service of the James Webb Telescope

And the most interesting thing is that these fascinating images full of implications were not produced for fun. On the contrary: they will serve as a very concrete working tool. Thesan will form a shock duo with the James Webb Space Telescope (JWST), the new darling of aerospace which is currently completing its final preparations.

“Many telescopes like the JWST are designed specifically to study this era”, explains Kannan. “This is where our simulations come in; they will help to interpret the actual observations and understand what we will see”, he specifies. And the stakes are extremely high: it’s about validate the global model on which our understanding of the universe is based, just that !

And this is where it gets interesting”, continues his colleague Mark Vogelsberger. “Our simulations could be consistent with the JWST observations; in this case, it would confirm the relevance of our modeling“, he explains. “Or there could be a significant difference, which would show that our understanding of the early universe is wrong. !”

But you shouldn’t be in a hurry; the first answers will not arrive immediately. We will have to start by waiting for the final commissioning of the telescope. It will then be necessary to wait until he fixes his objective on his first targets; at present, NASA still refuses to communicate the identity of its first object of study, which remains qualified as “super-secret”.

Once this step has been taken, each element will have to be recontextualized and then integrated into new models which will in turn be compared to Thesan. Only then can researchers finally obtain some answers to this decisive question. Suffice to say that the road remains long; but in the meantime, we can always console ourselves with fascinating works like this… and with the highly anticipated first images of the JWST, which should reach us within a few months.

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