Researchers have built a powerful new computer simulation, called Lumina, that recreates how the universe emerged from darkness, as described in a news release from MIT. Developed by scientists at MIT, Harvard University and other institutions, Lumina follows two billion years of early cosmic history across a region about 1.6 billion light-years wide. The research was published in the Monthly Notices of the Royal Astronomical Society.
As the universe expanded and cooled after the Big Bang, electrons combined with atomic nuclei to form neutral hydrogen. Then the universe entered a period known as the cosmic dark age. No stars had formed yet, and neutral hydrogen filled space, absorbing ultraviolet light. Lumina lets researchers study how this environment changed as the first stars, galaxies and black holes appeared.
The simulation covers a volume of 500 megaparsecs and tracks dark matter, gas, stars and radiation such as photons. It recreates two major transitions called re-ionization, in which energetic light strips electrons from atoms. The results suggest that early stars and galaxies were mainly responsible for ionizing hydrogen, while actively feeding supermassive black holes supplied the more intense radiation needed to ionize helium. According to the team, this is the first simulation to capture both processes together in one model.
Half a trillion elements
The researchers expanded earlier simulations to cover a much larger region and added a radiation transport model, which calculates how light travels through space and interacts with matter. The result contains about half a trillion elements, including dark matter particles and gas cells. The new simulation ran on Frontier, a supercomputer at Oak Ridge National Laboratory in Tennessee, using the equivalent of more than 100,000 CPU cores and around 15,000 GPUs at peak.
This gives scientists a detailed virtual universe to test against reality. The team is making Lumina available to other researchers, so its predictions about early cosmic structures can be compared with observations from existing and future telescopes. Because it simulates such a large volume, it can generate large populations of galaxies that match the big samples upcoming surveys will collect. The simulation may also help predict the patterns of gravitational waves produced by ancient galaxies and black holes, opening another way to study the universe's earliest chapters.