Smithsonian scientists just recreated the first 2 billion years of the Universe

Scientists have created one of the largest and most detailed simulations of the early universe ever developed, offering a remarkable new way to explore how the cosmos evolved after the Big Bang. Known as "Lumina," the simulation was built by researchers at the Center for Astrophysics | Harvard & Smithsonian to help astronomers interpret observations from powerful instruments such as the James Webb Space Telescope (JWST) and Nancy Roman Space Telescope.

The research, published in Monthly Notices of the Royal Astronomical Society, reconstructs the universe's first 2 billion years by modeling the interactions between ordinary matter, dark matter, and radiation. By comparing Lumina's predictions with observations from JWST, Roman, and other telescopes, scientists can evaluate how well existing theories explain cosmic evolution and identify discoveries that might challenge their understanding of the universe's fundamental laws.

Astronomers have spent centuries studying the sky and developing explanations for the formation of stars, galaxies, and other cosmic structures. Modern supercomputers now make it possible to turn these ideas into detailed simulations that predict how the universe should behave. When telescope observations agree with those predictions, they strengthen confidence in current theories. Unexpected differences, however, may point toward physical processes that scientists have yet to fully understand.

"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 the largest cosmological radiation hydrodynamics simulation ever produced. In simple terms, it uses powerful computers to calculate how gas, dark matter, and light influenced one another as the young universe developed. By following these interactions across the first 2 billion years after the Big Bang, researchers can examine how the earliest galaxies formed and how their activity changed the enormous clouds of gas surrounding them.

The simulation models a volume of space more than 100 times larger than those covered by earlier comparable projects. Its virtual universe spans a cube approximately 1.5 billion light-years on each side, providing a view of cosmic evolution on a scale comparable to the vast regions that today's most advanced telescopes can study.

Another major advance is Lumina's treatment of helium reionization, a process in which radiation strips electrons from helium atoms. For the first time, a simulation of this kind follows that transformation as it unfolds while simultaneously accounting for how it affects the surrounding universe. This allows scientists to study the relationship between evolving galaxies, radiation, and the gas that fills the space between them.

"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."

Recreating such an enormous portion of cosmic history demanded extraordinary computing resources. The team used more than 15,000 graphics processing units on Frontier, one of the world's fastest supercomputers, housed at Oak Ridge National Laboratory in Tennessee.

That processing power enabled the researchers to simulate an exceptionally large region of the early universe without sacrificing the fine detail needed to investigate individual galaxies and other important structures. As a result, Lumina can capture the broader evolution of the cosmos while also tracking processes involved in the formation of stars, galaxies, and black holes.

Beyond recreating cosmic history, Lumina provides a powerful new framework for investigating how the universe developed. Researchers plan to use it to explore the movement of gas between galaxies, the influence of radiation left over from the Big Bang, and the emergence of regions where stars formed at especially high rates.

By placing these predictions alongside observations from the James Webb Space Telescope, the Nancy Roman Space Telescope, and other instruments, scientists hope to build a more complete picture of the universe's earliest chapters. Any unexpected differences between the simulated cosmos and the real one could provide valuable clues, potentially revealing where current theories need to be refined or reconsidered.