Scientists are getting a new glimpse of how the first galaxies came to be. In a stunning new simulation, researchers charted the aftermath of the universe’s “dark age,” including the appearance of the first galaxies that began to shine about 380,000 years after the Big Bang.
Lumina, the program behind the simulation, catalogs 2 billion years of cosmic time and represents a decent chunk of the 13.8 billion-year-old history of our universe. The results were published Monday (Oct. 26) in the journal Monthly Notices of the Royal Astronomical Society.
“Other simulations cannot zoom in as far as this,” study co-author Mark Vogelsberger, a professor of physics at MIT, said in a statement. “The difference between the smallest and largest scales that we simulate is larger than in any other simulation.”
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A video published alongside the paper shows what the scientists saw. The team zoomed in on an area roughly 1.6 billion light-years wide to learn more about how the ingredients of space create galaxies.
This section of the Lumina simulation shows the gas temperature in different parts of the early universe, with redder areas showing active galaxy clusters.
(Image credit: Lumina simulation)
Lighting up the Cosmic Dark Age
In the earliest years of our universe, a fog of neutral hydrogen atoms gradually built up, blocking out the light of the first stars. The hydrogen served as a “shroud” and didn’t make light visible until galaxies began to form. This ancient, enshrouded period is known as the Cosmic Dark Age.
The video begins in the middle of this epoch, at roughly 45 million years after the Big Bang. Zooming in on one small part of the simulated universe, it slowly reveals a gassy halo giving way to young galaxies shining brightly within it. Included in the calculations are dark matter, stars, gas and radiation — all contributing to the reemergence of cosmic light.
“We see this is where the first galaxies form,” first author Oliver Zier, a former postdoctoral researcher and computational astrophysicist at MIT who is now at Harvard University, said in the statement. “And the first stars form in those first galaxies. Those stars then create radiation. The simulation then tracks that radiation, and we can zoom way out to see how that radiation travels out from stars, through the universe, until at some point it ionizes some neutral hydrogen.”
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Lumina aims to show off two phenomena key to the young universe’s history: hydrogen reionization and helium reionization — a first for a program of its kind. Reionization describes how the intergalactic medium, or the area between galaxies, changed from neutral hydrogen to negatively charged ions.
Hydrogen reionization took place when ultraviolet light from young stars and galaxies hit the hydrogen, removing negatively charged electrons from the hydrogen molecules — a process that also allowed light to shine through the fog. Helium reionization happened when supermassive black holes, which have a lot of energy, broke apart neutral helium molecules.
The team said the simulation could eventually be used to validate telescope observations of the early universe, especially those focused on mapping many galaxies at the same time.
Zier, O., Smith, A., Shen, X., Liu, R., Kannan, R., Koehler, S. M., Springel, V., Pakmor, R., Vogelsberger, M., Bulichi, T., & Hernquist, L. (2026). Introducing the lumina project: large-volume radiation-hydrodynamic simulations of the epochs of hydrogen and helium reionization. Monthly Notices of the Royal Astronomical Society, 552(4). https://doi.org/10.1093/mnras/stag1469
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