PREVIEW

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BY MARK WORGAN

Scientists have created one of the largest and most detailed simulations of the early universe, with a little help from the world’s most powerful space telescopes.

Called Lumina, the model recreates how ordinary matter, dark matter, and radiation interacted during the first two billion years after the Big Bang.

Researchers at the Center for Astrophysics | Harvard & Smithsonian hope to use it to test theories about how the universe evolved, comparing its predictions with observations from the James Webb Space Telescope (JWST), the Nancy Grace Roman Space Telescope and other instruments.

The research has been published in the Monthly Notices of the Royal Astronomical Society.
By checking whether the simulation matches what telescopes observe, astronomers can assess whether their existing theories explain the universe — or whether the evidence points to something new.

“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.”

Lumina is described by its creators as the largest cosmological radiation-hydrodynamics simulation ever produced. This type of model examines how gas, dark matter and light interact as stars and galaxies form.

It traces the emergence of the earliest galaxies and the changes they brought to the vast expanses of gas between them.

The simulation covers more than 100 times the volume of space included in previous comparable models. It represents a region roughly equivalent to a cube 1.5 billion light-years across on each side, on a scale comparable to that accessible to today’s most powerful telescopes.

It is also the first simulation of its kind to capture helium reionisation as it happened, while allowing the effects of that process to influence the universe as the model evolves.

Reionisation is the process through which radiation strips electrons from atoms, changing the state of matter across the cosmos. Understanding how hydrogen and helium underwent these changes helps scientists investigate how the universe developed from its early state into the one observed today.

“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.”

Building Lumina required more than 15,000 graphics processing units running on Frontier, one of the world’s fastest supercomputers, at Oak Ridge National Laboratory in Tennessee.
The computing power enabled the team to model an immense volume of the early universe while retaining enough detail to study the formation of galaxies, stars and black holes.

Astronomers have long used models to explain how cosmic structures form. Supercomputer simulations allow researchers to turn those theories into predictions that can be compared with real observations.

When the predictions match the evidence, confidence in existing explanations increases. When they do not, the differences can point towards gaps in scientists’ understanding.

The team intends to use Lumina as a platform for investigating further questions about cosmic evolution.

Future research will examine how gas moves between galaxies, how radiation from the Big Bang influenced the universe’s development and how regions of intense star formation emerged over time.

By combining large-scale simulations with observations from telescopes such as JWST and Roman, researchers hope to build a clearer picture of the universe’s earliest chapters.