Scientists launch Lumina simulation to model universe's first two billion years

A team of researchers led by Oliver Zier, an ITC Fellow at the Center for Astrophysics | Harvard & Smithsonian, has completed Lumina, a large-scale computer simulation that follows the universe’s first two billion years after the Big Bang. The model, which covers a cubic region about 1.5 billion light-years on a side, was run on the Frontier supercomputer at Oak Ridge National Laboratory using more than 15,000 graphics processing units at peak scale.

Lumina builds on the IllustrisTNG galaxy-formation framework and integrates gas dynamics, dark matter, galaxy formation and radiation transport. The simulation predicts that early stars and galaxies drove the reionisation of hydrogen, while active galactic nuclei powered by growing supermassive black holes caused the later reionisation of doubly ionised helium, altering the temperature and state of intergalactic gas.

The results reproduce key observational constraints on the universe’s thermal history and, because of its larger volume, allow researchers to study rare cosmic objects and regional variations. The team expects Lumina to help test theoretical models against observations from NASA’s James Webb Space Telescope and the upcoming Nancy Grace Roman Space Telescope.

"Lumina gives scientists a way to test theories against observations of distant galaxies and quasars," the authors noted in their paper published in the Monthly Notices of the Royal Astronomical Society on October 26, 2026.

The researchers caution that the simulation is a computational model, not a direct record of the past, and its predictions must be compared with actual observations to assess accuracy.