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Scientists unveil largest-ever simulation of our universe in aid of ESA's Euclid mission

The 'Flagship 2 galaxy mock' simulates over 3.4 billion galaxies, precisely matching Euclid's expected view across a third of the sky.

BY RAJ NAIK

PUBLISHED SEP 29, 2025

This visualization shows galaxies, composed of gas, stars and dark matter, colliding and forming filaments in the large-scale universe, providing a view of the Cosmic Web (Representative Cover Image Source: NASA Goddard Space Flight Center)

A global team of scientists has successfully generated the largest simulated galaxy catalog in history, an unprecedented computational feat designed to train and validate the operations of the European Space Agency's (ESA) Euclid mission. The new resource, dubbed the 'Flagship 2 galaxy mock,' features over 3.4 billion galaxies, meticulously reproducing what the powerful Euclid space telescope is expected to observe across a third of the sky, as per the Euclid Consortium.

Image extracted from the Euclid Flagship simulations catalogue. Each dot represents a galaxy: blue points mark galaxies at the centers of dark matter clumps, while red points denote satellites within them (Image Source: Euclid Consortium | Jorge Carretero & Pau Tallada)

Launched in July 2023, the Euclid mission is currently midway through a six-year observation period focused on mapping the "dark universe." To prepare for the flood of data, researchers, led by the Institute of Space Sciences (ICE-CSIC) and the Port d’Informació Científica (PIC), developed this synthetic universe, which mimics distant galaxies that emitted their light more than 10 billion light-years ago. The full catalog is now openly available on the CosmoHub platform.

Simulated Dark Matter in the Milky Way Halo (Image Source: NASA)

The simulation is crucial for astrophysicists aiming to construct a final 3D map of the universe. By replicating the "cosmic web," the large-scale structure of the universe, the catalog will allow scientists to test the standard cosmological model and significantly advance the understanding of elusive dark energy and dark matter. To build this virtual cosmos, the team employed computational models that tracked the movement of 4 trillion particles governed by gravity. Within that vast simulation, they identified 16 billion gravitationally bound objects, known as haloes, which were then populated with over 3.4 billion model galaxies. These models include more than 400 properties, such as brightness, position, and shape, providing an exquisite reproduction of the visible universe.

This image depicts a simulation of the ‘cosmic web’, the vast network of threads and filaments that extends throughout the Universe (Cover Image Source: ESA) — This image depicts a simulation of the ‘cosmic web’, the vast network of threads and filaments that extends throughout the Universe (Image Source: ESA)

Experts stress that the utility of this massive data set extends far beyond the Euclid project itself. “This is a huge step for the scientific community, since it is now accessible to everyone," said Jorge Carretero, a researcher at PIC. "It can be used as a reference simulation for other astronomical surveys and their combinations.” He adds that the catalog can "have many different scientific applications beyond the context of the Euclid mission.”

Euclid is an ESA (European Space Agency) mission with critical contributions from NASA that aims to explore two of the biggest mysteries about the universe today: dark matter and dark energy (Image Source: NASA)

The synthetic catalog will be a vital tool for developing software pipelines to extract cosmological data and for detailed studies of how galaxies form and evolve. “The main value of the Flagship catalogue is its comprehensive set of properties that have been derived per galaxy," points out Pablo Fosalba, a researcher at ICE-CSIC. "We have checked that many of these properties closely resemble what we see in observational data, but we are just starting to explore how far we can go in terms of predicting properties that future galaxy surveys will observe in great detail," as mentioned by the outlet.

via GIPHY

According to Yannick Mellier, the Euclid Consortium lead, these simulations "successfully meet the precision and accuracy necessary to challenge cosmological models to the true dark universe.” As the Euclid Consortium continues to refine the catalog, the initial 'Flagship mock' is already being used to test observational techniques and to connect the visible universe with its dark components, cementing its role as a cornerstone of large-scale future galaxy surveys.