Record-Scale Lumina Simulation Recreates the Universe’s First Two Billion Years

Astronomers have built what they describe as the largest simulation of its kind of the young universe, a digital model meant to show how the first stars and galaxies reshaped the gas around them during roughly the first two billion years after the Big Bang.

The project, called Lumina, comes from researchers at the Center for Astrophysics, Harvard and Smithsonian. It was described in a paper in the Monthly Notices of the Royal Astronomical Society and reported by Phys.org and ScienceDaily.

Lumina models a cube of space about 1.5 billion light-years on each side, more than 100 times the volume of earlier comparable simulations, according to both reports. Inside that volume it tracks ordinary gas, dark matter and radiation together, an approach known as radiation hydrodynamics, which is far more demanding than modeling gravity alone.

The goal is to capture a period astronomers call reionization. In the early universe, hydrogen and helium gas was mostly neutral. As the first stars, galaxies and black holes switched on, their intense ultraviolet light stripped electrons from those atoms, leaving the gas ionized, the state it remains in across most of intergalactic space today. Hydrogen and helium went through this change at different times, and Lumina is the first simulation of its kind to follow helium reionization while letting its effects feed back into the developing model, the researchers said.

Running it required serious computing power. The team used more than 15,000 graphics processors on Frontier, the supercomputer at Oak Ridge National Laboratory in Tennessee. A visualization released with the study shows a slice of the resulting cosmic web spanning about 650 million light-years.

The lead author is Oliver Zier, a fellow at the center’s Institute for Theory and Computation. In a statement carried by both outlets, he said the James Webb Space Telescope has turned the early universe into an exciting new frontier in astrophysics. Co-author Aaron Smith of the University of Texas at Dallas said that for the first time, researchers can follow both hydrogen and helium changing into their modern form across such an enormous volume.

The simulation is designed to be compared with what Webb is now seeing and with future observations from NASA’s Nancy Grace Roman Space Telescope. The researchers say they plan follow-up studies on how gas moves between galaxies and how star formation unfolded.

There are limits worth keeping in mind. Lumina is a model, not an observation, and its results depend on the physical assumptions built into it. Neither report describes any comparison with telescope data yet; that work is still ahead. Both outlets drew on the institution’s announcement rather than independent outside assessment.

Still, simulations at this scale give astronomers a way to test whether their picture of the early universe produces the galaxies and gas patterns telescopes actually find.