Researchers have used some of the most detailed simulations yet of the early universe to investigate how the first stars and galaxies formed. Led by researchers at the University of Bath in the U.K., alongside collaborators at the University of Chicago in the U.S. and the Institut d’Astrophysique de Paris in France, the MEGATRON project uses advanced simulations to explore how the first stars and galaxies lit up the previously dark cosmos and enriched it with the chemical elements that would later become the building blocks of everything around us.
Published in the Open Journal of Astrophysics, four studies from the MEGATRON project combine cutting-edge cosmological simulations with sophisticated models of radiation, chemistry and galaxy formation. Together, these constitute the collaboration’s first substantial body of published results, with further papers expected to follow.
The findings from the study of the first stars show that accurately capturing the interplay between starlight, gas and newly forged elements is essential for connecting two previously separate views of the early universe: observations of young galaxies by the James Webb Space Telescope (JWST) and the chemical clues preserved in ancient stars in and around the Milky Way—the galaxy that contains our solar system.
JWST provides a direct view of galaxies in the infant universe, while ancient stars act as a fossil record of cosmic history. By studying the chemical fingerprints of these ancient stars, astronomers can reconstruct the properties of the first stars and trace how they enriched the cosmos with the first chemical elements.
The simulations follow the evolution of a young galaxy that will eventually grow into a system similar in mass to the Milky Way. Using advanced computer models that simultaneously track the movement of gas, the propagation of starlight and the evolution of chemical concentrations, the team investigated how stars shape the gas in and around galaxies over billions of years.
The study suggests that simplified models may underestimate the influence of stellar radiation and complex chemical processes on the gas surrounding galaxies. By modeling these effects at exceptionally high resolution, the team resolved structures in the gas that are not captured by simpler models, helping to improve predictions for current and future astronomical observations.
A direct glimpse of the infant cosmos
Dr. Martin Rey of the Department of Physics at the University of Bath, a lead contributor to the MEGATRON collaboration, said, “The James Webb Space Telescope gives us a direct glimpse of the infant cosmos, while stellar archaeology allows us to study the relics of those earliest times in our own galactic neighborhood. MEGATRON provides a physical bridge between the two.”
The simulations begin with pristine gas containing no heavy elements, mirroring conditions shortly after the big bang. They then follow the birth of the first stars, the radiation they emit, the supernova explosions that mark their deaths and the dispersal of newly forged elements into subsequent generations of stars and galaxies.
Understanding this process is central to one of astronomy’s most fundamental questions: where the elements that make up today’s universe came from.
Rey said, “The elements that make our world and life possible—carbon, oxygen, iron and many others—were forged by stars. To understand where those elements came from, we need to understand how the first stars formed and enriched their surroundings. MEGATRON allows us to test these ideas directly by comparing detailed simulations with observations from JWST and the chemical fingerprints preserved in ancient stars.”
Looking ahead, the team plans to use MEGATRON to strengthen links between theory and emerging observational data. As JWST continues to transform our understanding of the earliest galaxies, large-scale stellar surveys will provide increasingly detailed information about ancient stars in and around the Milky Way.
Rey and his colleagues at Bath are already developing the next generation of simulations. The project has been awarded 40 million processor hours on the U.K.’s national supercomputers, equivalent to running 5 million laptops in parallel for a year. These resources will enable simulations with higher resolution and more complete physical models, allowing even more direct comparisons with JWST observations and the chemical fossil record preserved in ancient stars.
“MEGATRON provides a common physical framework for interpreting two of astronomy’s most exciting new datasets: JWST’s view of the earliest galaxies and the stellar fossil record,” said Rey. “Together, these complementary observations allow us to test competing models of the first stars in ways that weren’t previously possible.”
The MEGATRON project started in 2023 and is scheduled to run until 2030.
More information
MEGATRON: how the first stars can create an iron metallicity plateau in the smallest dwarf galaxies, The Open Journal of Astrophysics (2026). DOI: 10.33232/001c.169605
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New simulations connect the first stars to cosmic fingerprints still visible today (2026, September 30)
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