Scientists cannot watch the first galaxies form from start to finish. They can, however, compare telescope observations with models of the physical processes that might connect them. A paper published on 26 October 2026 presents Lumina, a computer simulation that follows a large region of the universe through roughly its first 2 billion years.
The model brings several processes together. It follows dark matter and gas as galaxies develop, while calculating how radiation from stars and active black holes moves through the gas between them. That gives researchers a way to explore a long period of cosmic change within one simulation.
When the gas between galaxies changed
Lumina begins about 45 million years after the Big Bang, during the period astronomers call the cosmic dark ages. At that stage, neutral hydrogen was widespread. As early stars formed, their ultraviolet light could remove electrons from hydrogen atoms. Scientists call this process reionization.
The change did not happen everywhere at once. In Lumina, light from early galaxies and stars drives most of the simulated hydrogen reionization. Later, more energetic radiation associated with actively feeding supermassive black holes drives a similar change in helium. These are findings within the model, rather than direct observations of every part of the early universe.
The researchers modeled a region 500 comoving megaparsecs across, roughly 1.6 billion light-years on a distance scale that accounts for the universe’s expansion. This wide view helps them follow both developing galaxies and the larger patterns of gas around them, according to MIT’s account of the research.
A model that observations can test
Lumina’s value lies in the questions it lets astronomers ask. If a simulation predicts a particular distribution of early galaxies or changes in intergalactic gas, researchers can compare those predictions with measurements from telescopes and other observations. The Lumina project describes this comparison as a central goal.
The paper reports that several broad outputs are consistent with existing observational constraints. That agreement is useful, but it does not establish that every simulated galaxy, black hole or patch of gas matches the real past. The model depends on its physical assumptions and on how it represents processes too small to calculate directly.
The newly published paper gives astronomers a more detailed framework for testing how the young universe developed. Its strongest findings will come from continued comparisons between the simulated history and observations, including those that future surveys may provide.
