Lumina simulation brings the early universe to life on a record-breaking scale

The James Webb Space Telescope (JWST) and Nancy Roman Space Telescope are revealing the universe’s earliest chapters in detail. To help astronomers understand what they are seeing, researchers at the Center for Astrophysics | Harvard & Smithsonian have developed “Lumina,” one of the largest and most detailed simulations ever created of the early universe.

Published in Monthly Notices of the Royal Astronomical Society, the new model recreates how ordinary matter, dark matter and radiation interacted during the universe’s first 2 billion years, giving scientists a new tool to test theories about how the cosmos evolved after the big bang. By comparing observations from JWST, Roman and other telescopes with Lumina’s predictions, astronomers can determine whether their understanding of the laws governing the universe remains accurate or whether new discoveries may require them to rethink existing theories.

For centuries, astronomers have observed the night sky and developed increasingly sophisticated models to explain how stars, galaxies and other cosmic structures form. Today, supercomputer simulations allow researchers to transform those theories into detailed predictions. When observations match those predictions, confidence in existing theories grows. When they do not, scientists gain opportunities to uncover new insights about how the universe works.

“With JWST, the early universe has become an exciting new frontier in astrophysics,” said lead author Oliver Zier, an ITC fellow at the Center for Astrophysics | Harvard & Smithsonian. “To understand what we are seeing with this telescope, we need to translate our theories into detailed predictions. After several years of work, with plenty of ups and downs, it is incredibly rewarding to see the simulation results and watch our predictions come to life in video.”

Reionization on an unprecedented scale

Lumina represents the largest cosmological radiation-hydrodynamics simulation ever created. This type of simulation models how the universe’s fundamental ingredients, including gas, dark matter and light, interact to form stars and galaxies. Lumina follows the first 2 billion years of cosmic history, tracing how the earliest galaxies emerged and transformed the vast regions of gas between them.

The simulation covers more than 100 times the volume of space modeled by previous comparable simulations. It is also the first to capture helium reionization as it occurred while allowing its effects to immediately influence the evolving universe within the model. The simulation encompasses a region equivalent to a cube roughly 1.5 billion light-years on each side, comparable to the scale astronomers can observe with today’s most powerful telescopes.

“We feel incredibly fortunate to be building simulations like Lumina,” said Aaron Smith, an assistant professor of physics at the University of Texas at Dallas and an author on the paper. “For the first time, we can follow along as both hydrogen and helium changed into their modern form across such an enormous volume of the universe, while still resolving the galaxies and other luminous objects driving that transformation.”

Supercomputer power for future cosmic tests

Creating Lumina required more than 15,000 graphics processing units running on Frontier, one of the world’s fastest supercomputers, located at Oak Ridge National Laboratory in Tennessee. Its computing power allowed researchers to model an unprecedented volume of the early universe while maintaining the level of detail needed to study the formation of galaxies, stars and black holes.

The research team designed Lumina as a platform for testing new ideas about the formation and evolution of the universe. Future studies will use the simulation to investigate how gases move between galaxies, how radiation from the big bang shaped cosmic evolution and how regions of intense star formation developed over time.

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