Visual impressions of the COLIBRE simulations. The panel on the left shows the so-called cosmic web, where the colour encodes the projected density of gas and stars. The two panels on the right zoom into two of the many galaxies formed in the simulations. These images show the stellar light obscured by dust for a disc galaxy seen face-on (top right) and another disc galaxy seen edge-on (bottom right). (c) Schaye et al. (2026)
New cosmological simulations developed by an international collaboration are offering the most realistic view yet of how galaxies form and evolve - thanks in large part to work led by Dr James Trayford of the University of Portsmouth, an astrophysicist who also specialises in "sonification": turning data into sound that can accompany visuals.
The team, led by astronomers from Leiden University, has unveiled COLIBRE, a new suite of cosmological simulations: virtual universes that offer the most realistic picture yet of how galaxies formed and evolved since the dawn of time.
The results, published in Monthly Notices of the Royal Astronomical Society , show that the standard cosmological model can successfully explain the observed growth of galaxies, from the first billion years after the Big Bang to the present day, when key missing physics is included.
Beyond traditional data products, the team has developed new ways to explore the simulations. This includes novel "sonified videos", where sound encodes additional physical information for richer insight into the galaxy formation process, as well as interactive maps that allow users to explore the virtual universes.
Video and sound available - click the link to hear an individual galaxy and a cluster of galaxies.
Dr James Trayford, from the University of Portsmouth's Institute of Cosmology and Gravitation, led the development of COLIBRE's dust model and the sonification of its data.
He said: "One of the unique and exciting outputs from COLIBRE is our videos which use sound as well as visuals to communicate the data. This helps us communicate more about what's going on inside galaxies, and reveal how these processes interact. As well as seeing a galaxy's structure, we can hear changes in key processes like stars being born, black holes growing, and powerful bursts of energy flowing out into space. Sound adds another layer of information that helps reveal the underlying physics beyond what we can visualise.
"These tools could provide new insights, make our field more accessible, and help us build intuition for how galaxies grow and evolve."
The sound development is part of the Ear to the Sky project based in Portsmouth, and uses free, open-source software called STRAUSS, which was also developed here and has just received another year of funding.
Unlike earlier simulations, COLIBRE can model the cold gas and cosmic dust inside galaxies, the raw materials from which stars form and which strongly affect how galaxies look in telescopes. By including these missing ingredients and using far more computing power than before, the simulations successfully reproduce real galaxies seen both today and in the early universe by the James Webb Space Telescope (JWST).
The results show that our standard model of the universe can explain galaxy formation more accurately than previously thought, while also opening up powerful new ways to compare theory with observations and to explore a virtual universe through visuals, sound, and interactive tools.
Digital cold gas and dust grains
According to the scientists the COLIBRE simulations break new ground in several ways. Earlier simulations prevented gas inside galaxies from cooling below about 10,000 degrees, hotter than the surface of the Sun, because modelling colder gas was too complex. Yet observations show that stars form in much colder gas. COLIBRE includes the additional physics needed to model this cold interstellar gas directly.
COLIBRE also simulates small dust grains, that can greatly influence galactic gas. These solid particles can help hydrogen molecules to form, which dominate the cold gas content of galaxies. The dust also shields gas from harsh ultraviolet radiation and strongly affects how galaxies appear in telescopes. Dust absorbs ultraviolet and optical light from stars and re-emits it in the infrared, shaping many astronomical observations. By modelling dust directly, COLIBRE opens new ways to compare simulations with real data.
Thanks to advances in algorithms and supercomputing, COLIBRE uses up to 20 times more resolution elements than earlier simulations, allowing larger volumes to be simulated in greater detail and with better statistics. Dark matter is also simulated in high resolution, reducing artefacts seen in previous simulations.
A new laboratory
COLIBRE demonstrates that a realistic treatment of cold gas, dust, and feedback from stars and black holes is crucial for understanding galaxy evolution. It provides a powerful new laboratory for testing theories, interpreting observations, and creating "virtual observations" to check how astronomers analyse real data.
"Much of the gas inside real galaxies is cold and dusty, but most previous large simulations had to ignore this," said Prof. Joop Schaye of Leiden University, who led the project. "With COLIBRE, we finally bring these essential components into the picture."
COLIBRE shows that the standard cosmological model remains consistent with observations of galaxy evolution, including some that were thought to be challenging, such as the masses of galaxies in the early universe. "Some early JWST results were thought to challenge the standard cosmological model," said Dr. Evgenii Chaikin of Leiden University, lead author of several accompanying COLIBRE papers and a co-author of the main study. "COLIBRE shows that, once key physical processes are represented more realistically, the model remains consistent with what we see."
Still not everything is explained yet. The enigmatic "Little Red Dots" discovered by JWST, possibly the seeds of supermassive black holes, are not predicted by COLIBRE, which assumes such seeds already exist. Modelling their formation will require even higher resolution simulations and new physics, pointing the way for future work.
The simulations were run using the SWIFT simulation code on the COSMA8 supercomputer in the UK. The largest simulation required 72 million CPU hours, and the full model took nearly 10 years to develop by an international team spanning Europe, Australia, and the United States. The scientists point out that it will take years to analyse the data that has already been produced. Most simulations were completed in 2025, although the simulations with the highest resolution are still running and will probably not finish before this summer.
