A new cosmological simulation developed by scientists at the Harvard-Smithsonian Center for Astrophysics is offering an unprecedented view of the universe’s first 2 billion years, tracing how matter, dark matter and radiation interacted to shape the earliest galaxies and transform the cosmos after the Big Bang.

Named Lumina, the simulation is the largest of its kind, modeling a cube of space measuring approximately 1.5 billion light-years on each side, a volume about 100 times greater than that covered by previous simulations of a similar type.

Its scale and level of detail allow scientists to investigate how the first galaxies formed, how radiation from stars and growing black holes altered their surroundings, and how the universe’s chemical composition evolved over time.

Visualizations generated by Lumina show intricate filaments of dark matter intertwined with rapidly moving gas, revealing how the earliest cosmic structures emerged and developed.

The model also enables researchers to trace changes in hydrogen and helium, including a major phase in cosmic history known as helium reionization.

In the early universe, matter existed in an extremely hot, dense state following the Big Bang.

As the universe expanded and cooled, electrons combined with atomic nuclei to form electrically neutral atoms.

Hundreds of millions of years later, the first stars and galaxies began to emerge, producing intense ultraviolet radiation capable of stripping electrons from atoms and ionizing hydrogen and helium.

As radiation from stars and black holes at the centers of galaxies spread through space, regions of ionized gas expanded and eventually merged, transforming the surrounding intergalactic environment.

Lumina allows scientists to examine helium reionization across an enormous volume of space while retaining enough detail to resolve the galaxies and other luminous objects responsible for driving the process.

Dr Aaron Smith, a physicist at the University of Texas at Dallas and co-author of a paper on Lumina, said the simulation provides a new opportunity to study these changes on an unprecedented scale.

“We feel incredibly fortunate to be building simulations like Lumina.

“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.”

To achieve this combination of scale and detail, the research team used 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 resources enabled researchers to simulate a vast region of the universe while retaining the resolution needed to investigate the formation of stars, galaxies and black holes.

The results come as observations from the James Webb Space Telescope (JWST) have made the early universe an increasingly important frontier in astrophysics, creating a need for detailed theoretical models that can be tested against what telescopes detect.

Dr Oliver Zier, lead author of the research paper and a scientist at the Harvard-Smithsonian Center for Astrophysics, said simulations are essential for interpreting these observations.

“With the James Webb Space Telescope (JWST), the early universe has become an exciting new frontier in astrophysics.

“To understand what we are seeing with this telescope, we need to translate our theories into detailed predictions.”

By comparing telescope observations with the predictions generated by Lumina, researchers can assess whether existing theories accurately explain the universe’s evolution.

Agreement between simulations and observations would strengthen confidence in those theories, while significant discrepancies could point to gaps in scientists’ understanding of the processes that shaped the early cosmos.

The Nancy Grace Roman Space Telescope is also expected to contribute to observations that can be compared with theoretical models, providing further opportunities to investigate the universe’s earliest stages.

The research builds on the broader framework of the Big Bang theory, which describes the universe’s evolution from an initially hot, dense state approximately 13.8 billion years ago.

Evidence supporting the theory includes observations by Edwin Hubble in the 1920s showing that galaxies are generally moving away from one another, indicating that the universe is expanding.

Another key discovery came in 1964, when Arno Penzias and Robert Wilson detected the cosmic microwave background, the relic radiation released when the universe became transparent to light roughly 380,000 years after the Big Bang.

The observed abundance of light elements, including hydrogen and helium, provides additional evidence consistent with the theory.

Together, these observations establish the foundation for modern cosmology, while simulations such as Lumina help researchers investigate how the universe developed from its early conditions into the complex structures visible today.