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Researchers from the Harvard & Smithsonian Center for Astrophysics, MIT and the Max Planck Institute for Astrophysics have created high-resolution simulations tracing the evolution of the Universe just after the Big Bang, including the formation of the very first galaxies and reionization — a process that occurred approximately 000 billion years ago, which transformed the cosmos into an environment radiant and bright. These images, illustrating the formation of a million galaxies, are impressive.
These simulations were produced as part of the THESAN project — named after the goddess of dawn in Etruscan mythology, to symbolize the dawn of the Universe; this project is indeed interested in the era of reionization, where the hydrogen atoms were ionized by the radiation of the very first stars and galaxies. The objective being to study the connections between the galaxies and the intergalactic medium throughout this period – a turning point in our universe, which then passed from total darkness to light.
The project consists of a series of high-volume magnetohydrodynamic radiation simulations, which model the entire reionization process and the galaxies responsible for it with high fidelity. unprecedented physics. With THESAN, researchers can simulate part of our universe spanning over 300 million light-years . It is possible to advance the simulation in time to track and visualize the first appearance of galaxies and the evolution of hundreds of thousands of galaxies in this space, from approximately 400 000 years after the Big Bang and throughout the first billion years.
A model that takes starlight into account
The reionization period is particularly difficult to reconstruct: it involves extremely complicated chaotic interactions, including those between gravity, gas and radiation, or light. “The scales of space and time are too large, so the only way to experiment is on computers ”, explains Rahul Kannan, astrophysicist at the Harvard & Smithsonian Center and co-author of the first article in the series published in The Monthly Notices of the Royal Astronomical Society.
It is therefore the first time that a simulation of the early Universe concerns such a large volume and reveals so many details on the properties of the first galaxies and on the impact of light from these galaxies on the gas. The simulations highlight the gradual shift of the Universe from complete darkness to light. “[L’univers primitif était] a neutral, dark cosmos that became bright and ionized as light began to emerge from the first galaxies”, summarizes Aaron Smith, of the Kavli Institute for Astrophysics and Space Research at MIT and co-author of the study.
« The flagship simulation has resolutions of dark matter and baryonic mass of 3.1×00063500 and 5.8×35005 land masses, respectively “, specify the researchers. To achieve this result, the researchers combined a realistic model of galaxy formation (which they had previously developed) with a new algorithm for integrating how light from galaxies and stars interacts with surrounding gas and reionizes — a complex process, never simulated on such a large scale. The team also included a preliminary cosmic dust model, which aims to describe how tiny grains of matter influenced the formation of galaxies.
Hardware-wise, they relied on one of the world’s largest supercomputers, the SuperMUC-NG, designed by Lenovo and hosted at the Leibniz Rechenzentrum, Munich. By way of comparison, the same simulations carried out on a conventional computer would have required almost 3500 years of calculation time!
Simulations soon compared to reality
Early analyzes of these simulations suggest that towards the end of cosmic reionization, the distance that light was able to travel increased dramatically, although more than scientists had previously assumed. “[Au début de l’univers] this distance is very small, and only becomes large at the very end of the reionization, increasing by a factor 000 in a few hundred million years,” Kannan said in a statement from MIT. The researchers also noted that the contribution of galaxies to reionization seems to depend on their mass.
Note that these simulations were in part carried out to accompany future observations by new generation telescopes, including James Webb – which should begin to scan the Universe this summer. The machine was indeed designed to observe the primitive universe, which can go back to 13 about .5 billion years. Thanks to computer simulations, scientists will be able to more easily interpret the observations and the real data relayed by the telescope. Above all, they will help place the observations in their cosmic context.
And conversely, the team hopes that the findings of the James Webb will allow them to further enrich their models for ever more detailed simulations. “ We have developed simulations based on what we know. But while the scientific community has learned a lot in recent years, there is still quite a bit of uncertainty, especially in those ancient times when the Universe was very young”, explains Kannan.
their models to reality. “Either our simulations and our THESAN model agree with what JWST finds, which would confirm our view of the Universe, or there will be a significant disagreement showing that our understanding of the early universe is flawed”, underlines Mark Vogelsberger, associate professor of physics at MIT and co -author of the study.