New MEGATRON Simulations Link First Stars to Fingerprints Still Visible in Today's Universe

Four papers in the Open Journal of Astrophysics mark the first substantial body of published results from MEGATRON, a simulation project that tries to reconstruct how the earliest stars and galaxies lit up a dark universe and seeded it with the chemical elements that later made up everything around us. Further papers from the collaboration are expected.

The work is led by researchers at the University of Bath in the U.K., with collaborators at the University of Chicago in the U.S. and the Institut d'Astrophysique de Paris in France. The studies pair cosmological simulations with detailed models of radiation, chemistry and galaxy formation.

The aim is to connect two views of the early universe that have largely been kept apart. One comes from the James Webb Space Telescope, which looks directly at galaxies in the infant cosmos. The other comes from ancient stars in and around the Milky Way, which serve as a fossil record. Their chemical fingerprints let astronomers reconstruct the properties of the first stars and trace how those stars spread the first elements.

The simulations begin with pristine gas containing no heavy elements, mirroring conditions shortly after the big bang. From there they follow the birth of the first stars, the radiation those stars emit, the supernova explosions that end their lives, and the scattering of newly forged elements into later generations of stars and galaxies. The team followed a young galaxy that is expected to grow into a system comparable in mass to the Milky Way, tracking gas motion, the propagation of starlight and the changing chemical makeup together, over billions of years.

One conclusion concerns method. According to the team, simpler models may underestimate how strongly stellar radiation and complex chemical processes affect the gas surrounding galaxies. Working at exceptionally high resolution, the researchers resolved structures in that gas that simpler approaches do not capture, which they say should improve predictions for current and future observations.

Dr. Martin Rey of the Department of Physics at Bath, a lead contributor, described the project as a bridge. JWST, he said, offers a direct glimpse of the infant cosmos, while stellar archaeology studies relics of those times in our own galactic neighborhood, and MEGATRON provides a physical link between them. He noted that carbon, oxygen, iron and many other elements were forged by stars, so understanding their origin means understanding how the first stars formed and enriched their surroundings. In his words, the framework lets researchers test competing models of the first stars in ways that were not possible before.

The next phase is already under way. Rey and his Bath colleagues are developing a new generation of simulations, backed by an award of 40 million processor hours on the U.K.'s national supercomputers, which the team equates to running 5 million laptops in parallel for a year. The extra capacity is meant to bring higher resolution and fuller physics, allowing closer comparison with JWST data and with the chemical record in ancient stars. Large-scale stellar surveys are expected to supply increasingly detailed data on those stars.

MEGATRON began in 2023 and is scheduled to run until 2030, so the comparisons between simulation and observation are likely to sharpen over the coming years as more papers appear.