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    "headline": "Lumina simulation replays the universe’s first 2 billion years; galaxies and black holes ended the dark",
    "description": "The Lumina simulation from MIT, Harvard and partners models the universe's first 2 billion years, capturing hydrogen and helium reionization together.",
    "datePublished": "2026-11-12T10:37:00+00:00",
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    "keywords": "Frontier supercomputer, Lumina simulation, Mark Vogelsberger, MIT, Reionization",
    "articleBody": "A single computer run with half a trillion moving parts has replayed the universe’s first 2 billion years, and it points to two different engines that cleared the fog hiding early light. The Lumina simulation, built by physicists from MIT, Harvard and partner institutes, finds that ultraviolet light from young galaxies stripped hydrogen of its electrons, while far fiercer radiation from feeding supermassive black holes did the same job on helium. The team says no earlier simulation captured both transitions, called hydrogen and helium reionization, inside one model. Lumina’s volume is about 100 times larger than the previous best simulations, according to the MIT announcement of the paper, which appears in the Monthly Notices of the Royal Astronomical Society. What the cosmic dark ages were Roughly 380,000 years after the Big Bang, the cooling universe filled with neutral hydrogen. That gas soaked up light at key wavelengths, and the cosmos slipped into what astronomers call the dark ages. Reionization is the later era when the first stars and galaxies poured out enough ultraviolet light to ionize that gas again and make intergalactic space transparent. Standard estimates put it between about 150 million and 1 billion years after the Big Bang, with helium following later. How Lumina was built Lumina starts about 45 million years after the Big Bang, deep in the dark ages, and runs forward for 2 billion years. Its box of early cosmos is about 500 megaparsecs, or roughly 1.6 billion light-years, across. Inside it, the code follows dark matter, gas, stars and photons at the same time. The model grows out of IllustrisTNG, an earlier galaxy-formation code developed partly at MIT. The Lumina team kept that code’s galaxy-level detail, spread it over a far bigger volume and coupled it to a radiation-transport model that tracks ultraviolet light across cosmic distances. The result holds about half a trillion dark-matter particles and gas cells, around 30 times the resolution of IllustrisTNG. It ran on Frontier, the supercomputer at Oak Ridge National Laboratory in Tennessee. “At peak scale, the calculation brings together the equivalent of more than 100,000 CPU cores and around 15,000 GPUs,” said MIT co-author Xuejian (Jacob) Shen. First author Oliver Zier, formerly a postdoctoral researcher with MIT physicist Mark Vogelsberger, walked through what the zoom shows: gas falling into dark matter haloes, galaxies taking shape there, their first stars switching on, and the simulation following that starlight outward “until at some point it ionizes some neutral hydrogen.” Why it matters Telescopes now photograph galaxies from the reionization era, but each image is a frozen moment. A model that grows huge numbers of galaxies in a realistic slab of space gives astronomers a reference to test those pictures against. “It produces enormous populations of simulated galaxies, finally allowing us to make comparisons with the very large galaxy samples that upcoming surveys will observe,” Shen said. For a sense of scale, take the Milky Way’s disk as roughly 100,000 light-years wide: 1.6 billion divided by 100,000 means Lumina’s box spans about 16,000 Milky Ways laid end to end. The team is releasing Lumina to other researchers and plans to use it to map the large-scale structure of the young universe and to predict gravitational-wave patterns from early galaxies and black holes. Black holes have been busy in Badiyaa’s science coverage lately, from pulsar timing hints that supermassive black hole pairs merge despite the final parsec problem to the much nearer milestone of Voyager 1 reaching one light-day from Earth. Limits of the model Lumina is a calculation, not an observation. Its starting conditions approximate what physicists expect the dark ages looked like, so the split it finds, with galaxies driving hydrogen reionization and black holes driving helium reionization, is a prediction to be checked against real sky surveys. Astronomers also still debate which sources supplied most of the ionizing light, with dwarf galaxies, the very first generation of stars and quasars all proposed. What the team claims for certain is reach. “The difference between the smallest and largest scales that we simulate is larger than in any other simulation,” Vogelsberger said. Further reading MIT News: Watch the universe emerge from the dark ages, with Lumina Wikipedia: Reionization Image: Oak Ridge National Laboratory, CC BY 2.0 via Wikimedia Commons This article was produced with AI assistance and reviewed by our Editorial Desk. How we work.",
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