Lumina simulation tracks the early universe's transformation from darkness

A team of researchers from MIT, Harvard University, and other institutions has developed a large-scale computer simulation called Lumina that models the early universe from about 45 million years after the Big Bang through 2 billion years of evolution. The simulation covers a region roughly 1.6 billion light-years wide and follows the formation of galaxies, the spread of radiation, and the transition of the universe from a state filled with neutral hydrogen to one increasingly transparent to ultraviolet light.

The work, published in the Monthly Notices of the Royal Astronomical Society, focuses on two key processes: hydrogen re-ionization and helium re-ionization. In the early universe, neutral hydrogen filled space and absorbed ultraviolet light. As the first stars and galaxies formed, their ultraviolet radiation stripped electrons from hydrogen atoms, making the gas ionized and allowing radiation to travel across much greater distances. The simulation indicates that early stars and galaxies drove hydrogen re-ionization, while actively feeding supermassive black holes supplied the more energetic radiation needed to ionize helium.

Lumina builds on the earlier IllustrisTNG simulation by upgrading its software to cover a much larger volume while maintaining high resolution. The model contains roughly half a trillion elements, including dark matter particles and gas cells, and provides about 30 times the resolution of IllustrisTNG in a volume 100 times larger than previous leading simulations. Running the simulation required the Frontier supercomputer at Oak Ridge National Laboratory, using the equivalent of more than 100,000 CPU cores and around 15,000 GPUs.

The researchers have made Lumina available to other scientists so its predictions can be compared with observations from existing and future telescopes. The team plans to use the simulation to study the large-scale arrangement of matter in the early universe and to predict patterns of gravitational waves from ancient galaxies and black holes. Because Lumina generates extensive populations of simulated galaxies, it can be directly compared with the large galaxy samples that upcoming surveys are expected to collect.