Lumina Simulation Recreates the Early Universe at Record Scale, Testing Cosmic Theories Against JWST Data

Researchers at the Center for Astrophysics | Harvard & Smithsonian have built a simulation of the early universe called Lumina, which they describe as one of the largest and most detailed ever made. It was designed to meet a specific need. The James Webb Space Telescope and the Nancy Roman Space Telescope are showing the universe's earliest chapters in increasing detail, and astronomers need predictions to measure those observations against.

The work appears in Monthly Notices of the Royal Astronomical Society. Lumina recreates how ordinary matter, dark matter and radiation interacted during the universe's first 2 billion years. Scientists can compare what JWST, Roman and other telescopes see with what the model predicts. If the two agree, confidence in current understanding of the laws governing the universe grows. If they diverge, it may be a sign that existing theories need rethinking.

That is how the field has long worked. Astronomers have watched the night sky for centuries and built ever more sophisticated models of how stars, galaxies and other structures form. Supercomputer simulations now turn those theories into detailed, testable predictions, and a mismatch is an opening to learn something new.

Lead author Oliver Zier, an ITC fellow at the Center for Astrophysics, said JWST has made the early universe an exciting new frontier. To understand what the telescope sees, he said, theories have to be translated into detailed predictions. He described several years of work with plenty of ups and downs, and called it incredibly rewarding to watch the predictions come to life in video.

Technically, Lumina is the largest cosmological radiation-hydrodynamics simulation ever created. That class of simulation models how gas, dark matter and light interact to form stars and galaxies. Lumina traces the first 2 billion years of cosmic history, following how the earliest galaxies emerged and changed the vast regions of gas between them.

The scale is the headline. The simulation covers more than 100 times the volume modeled by previous comparable efforts, a cube roughly 1.5 billion light-years on each side, comparable to the scale astronomers can observe with today's most powerful telescopes. It is also the first to capture helium reionization as it happened while letting the effects feed immediately back into the evolving model universe.

Aaron Smith, an assistant professor of physics at the University of Texas at Dallas and a paper author, said that for the first time researchers can follow both hydrogen and helium changing into their modern form across such an enormous volume, while still resolving the galaxies and other luminous objects driving that change.

The computing demands were large. Lumina ran on more than 15,000 graphics processing units on Frontier, one of the world's fastest supercomputers, at Oak Ridge National Laboratory in Tennessee. That power let the team model an unprecedented volume while keeping enough detail to study the formation of galaxies, stars and black holes.

The team intends Lumina as a platform rather than a single result. Future studies will use it to examine how gases move between galaxies, how radiation from the big bang shaped cosmic evolution, and how regions of intense star formation developed. The next test is the comparison with JWST and Roman data.