Visual impression of the dynamic range in the high-resolution COLIBRE simulation L025m5 at redshift z = 0.1. The top left panel shows a projection of the entire simulation with the colour encoding baryon surface density. The other panels zoom into different regions and show the stellar light in HST colours accounting for attenuation by dust.
Hi-Res Zoomable Version
Image Credit: Schaye et al. (2026)
Scientific Frontline: Extended "At a Glance" Summary: COLIBRE Cosmological Simulations
The Core Concept: COLIBRE is a groundbreaking set of advanced cosmological simulations that models the evolution of galaxies by integrating cold interstellar gas and cosmic dust, offering the most realistic digital representation of galaxy formation from the early universe to the present day.
Key Distinction/Mechanism: Unlike previous large-scale models that were limited to simulating gas at temperatures of 10,000 Kelvin or higher, COLIBRE directly models the physical and chemical processes of cold gas and microscopic dust grains. Utilizing up to 20 times more resolution elements than earlier frameworks, it accurately reproduces complex real-world observations, including those captured by the James Webb Space Telescope (JWST).
Major Frameworks/Components:
- Cold Interstellar Gas Modeling: Direct computational simulation of the low-temperature gas where actual stellar formation occurs, overcoming the computational limitations of previous high-temperature models.
- Cosmic Dust Integration: Simulation of dust grains that catalyze the formation of hydrogen molecules, shield gas from harsh ultraviolet radiation, and re-emit absorbed starlight as infrared energy.
- High-Resolution Supercomputing: Execution via the SWIFT simulation code on advanced supercomputer architecture, consuming up to 72 million CPU hours for the largest iterations to generate vast cosmic volumes with high statistical accuracy.
- Standard Cosmological Model Validation: Confirms that the standard theoretical framework of cosmology aligns with observational data once essential localized physical processes (like cold gas and dust) are properly represented.
Branch of Science: Astrophysics, Cosmology, and Computational Physics.
Future Application: COLIBRE will serve as a robust "virtual laboratory" for astronomers to test theoretical models and interpret complex datasets from modern sky surveys. Future iterations of the model will demand even higher resolutions to decode remaining astronomical mysteries, such as the formation of the JWST-discovered "Little Red Dots" (potential seeds of supermassive black holes). Additionally, the project's data outputs—including sonified videos and interactive maps—pioneer new methodologies for exploring and visualizing massive datasets.
Why It Matters: By accurately incorporating the fundamental "raw materials" of galaxy formation, COLIBRE bridges a critical gap between theoretical cosmological models and empirical astronomical observations. It decisively validates the standard cosmological model and provides researchers with the most precise tool to date for analyzing the physical building blocks and evolutionary history of the universe.
Leiden scientists lead COLIBRE, a groundbreaking set of cosmological simulations. By including key missing physics, cold gas and cosmic dust, they offer the most realistic picture yet of how galaxies formed and evolved since the dawn of time.
Unlike earlier simulations, COLIBRE models cold gas and cosmic dust inside galaxies. By including these ‘raw materials’ and using far more computing power, it successfully reproduces galaxies observed today and in the early universe by the James Webb Space Telescope (JWST). The results, published in Monthly Notices of the Royal Astronomical Society, show that the standard cosmological model can explain galaxy formation and growth more accurately than previously thought. Only a few crucial pieces of physics were still missing.
Visual impressions of the COLIBRE simulations. The left panel shows the cosmic web, with colours representing the density of gas and stars. The right panels zoom in on two galaxies: top shows the stellar light obscured by dust for a disc galaxy seen face-on the bottom shows another disc galaxy seen edge-on. (c) Schaye et al. (2026)
Digital cold gas and dust grains
Earlier simulations couldn’t let gas inside galaxies cool below about 10,000 degrees Kelvin, hotter than the Sun’s surface, because colder gas was too complex to model. Yet, observations show that stars form in much colder gas. COLIBRE includes the physical and chemical processes needed to model this cold interstellar gas directly.
COLIBRE also simulates small dust grains, which strongly influence galactic gas. Dust helps form hydrogen molecules, which dominate the cold gas content of galaxies. It also shields gas from harsh ultraviolet radiation and strongly affects how galaxies appear in telescopes.
How does radiation affect our observations of galaxies?
Dust namely absorbs ultraviolet and optical light from stars and re-emits it in the infrared, shaping many astronomical observations. By modeling dust directly, COLIBRE opens new ways to compare simulations with real data. Dust namely absorbs ultraviolet and optical light from stars and re-emits it in the infrared, shaping many astronomical observations. By modeling 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. This lets scientists simulate larger volumes with greater detail and better statistics.
Exploring galaxies in a virtual laboratory
COLIBRE shows that realistically modeling cold gas, dust, and outflows form stars and black holes are crucial for understanding galaxy evolution. It provides a powerful new ‘laboratory’ for testing theories, interpreting observations, and creating virtual observations to check how astronomers analyze real data.
‘With COLIBRE, we finally bring these essential components into the picture.’
‘Much of the gas inside real galaxies is cold and dusty, but most previous large simulations had to ignore this,’ says project leader Joop Schaye, from the Leiden Observatory. ‘With COLIBRE, we finally bring these essential components into the picture.’
The simulations confirm that the standard cosmological model remains consistent with observations of galaxy evolution, including some previously thought to be challenging, such as the masses of early galaxies. ‘But COLIBRE shows that, once key physical processes are represented more realistically, the model matches what we see,’ says Evgenii Chaikin of the Leiden Observatory, lead author of several accompanying COLIBRE papers.
Leiden physicist Matthieu Schaller focused on simulation software and running large-scale simulations. ‘For me, these results are remarkable, as they represent the most realistic simulations of the universe ever made’, he says. ‘They will teach us more about the link between astrophysical observations and cosmology and the fundamental building blocks of our universe. They provide a crucial tool for interpreting modern survey data.’
Pushing the limits of cosmic simulations
Some mysteries remain. The enigmatic ‘Little Red Dots’ discovered by JWST, possibly the seeds of supermassive black holes, are not predicted by COLIBRE, which assumes these seeds already exist. Modeling their formation will require even higher resolution simulations and new physics, pointing out the way for future work.
The simulations were run using the SWIFT simulation code on the COSMA8 supercomputer, at the DiRAC national facility 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 across Europe, Australia, and the United States. It will take years to fully analyze the massive data set. Most simulations finished in 2025, although the highest resolution runs are still ongoing and expected to be completed after the summer.
‘We’re excited not just about the science, but also about creating new ways to explore it.’
A universe you can see and hear
Beyond traditional data, the team created new ways to explore the simulations. This includes ‘sonified videos’, in which the simulation data is converted into sound so that the universe can be “heard,” and interactive maps that allow users to explore the virtual universes.
‘We’re excited not just about the science, but also about creating new ways to explore it,’ concludes James Trayford of the University of Portsmouth, who led the dust modeling and sonification efforts. ‘These tools provide new insights, make our field more accessible, and help us build intuition for how galaxies grow and evolve.’
Published in journal: Monthly Notices of the Royal Astronomical Society (1&2)
Title:
- The COLIBRE project: cosmological hydrodynamical simulations of galaxy formation and evolution
- COLIBRE: calibrating subgrid feedback in cosmological simulations that include a cold gas phase
Authors:
- Joop Schaye, Evgenii Chaikin, Matthieu Schaller, Sylvia Ploeckinger, Filip Huško, Robert J. McGibbon, James W. Trayford, Alejandro Benítez-Llambay, Camila Correa, Carlos S. Frenk, Alexander J. Richings, Victor J. Forouhar Moreno, Yannick M. Bahé, Josh Borrow, Anna Durrant, Andrea Gebek, John C. Helly, Adrian Jenkins, Cedric G. Lacey, Aaron Ludlow, Folkert S. J. Nobels
- Evgenii Chaikin, Joop Schaye, Matthieu Schaller, Sylvia Ploeckinger, Yannick M. Bahé, Alejandro Benítez-Llambay, Camila Correa, Victor J. Forouhar Moreno, Carlos S. Frenk, Filip Huško, Roi Kugel, Robert McGibbon, Alexander J. Richings, James W. Trayford, Josh Borrow, Robert A. Crain, John C. Helly, Cedric G. Lacey, Aaron Ludlow, Folkert S. J. Nobels
Source/Credit: Leiden University
Reference Number: asph041326_01
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