We’re thrilled to announce a major milestone for the ARRAKIHS Project. The HARKONENS Project is led by Santi Roca Fábrega (Lund University, Sweden) in close collaboration with Corentin Cadiou (IAP, France), has been awarded an extraordinary 234 million CPU hours on the EuroHPC supercomputing infrastructure. Many members of the COS team are actively involved, making this a remarkable collective achievement and an important milestone for our mission.
This success represents a major step forward for ARRAKIHS’s theoretical effort. The HARKONENS project will launch the first generation of a new suite of cosmological simulations of Milky Way–mass halos. These simulations have been designed specifically to address the scientific goals of ARRAKIHS on the study of Low Surface Brightness universe structures, while capturing the diversity of assembly histories expected for galaxies similar to our own, exploring the spread in the stellar-to-halo mass relation, and testing reasonable variations in both dark matter models and baryonic-physics prescriptions. The HARKONENS simulations will follow in detail the formation of stellar streams, the low mass satellite galaxies, and the evolution of the accreted stellar, providing the theoretical context needed to interpret the faint low-surface-brightness structures that the mission will observe.
With the allocation granted, 234 million CPU hours (a unit that measures how long the processors of a supercomputer can work to run complex calculations) from EuroHPC, effectively reaching around 250 million thanks to additional time from the Spanish Supercomputing Network on the same system (MareNostrum 5), the team will be able to run the first substantial set of models within a much larger long-term program. This initial phase will deliver the first generation of high-resolution simulations, a scale and depth not previously achievable, and essential for connecting ARRAKIHS’s observations with predictions from cosmological theory. These simulations has begun on 10 October 2025, marking the start of a twelve-month period dedicated to producing the theoretical backbone that will accompany the mission’s future data.
About EuroHPC JU
The EuroHPC Joint Undertaking, Europe’s flagship high-performance computing initiative, supports pioneering scientific work across the continent. Competition for its resources is intense, and receiving an allocation of this magnitude requires projects of exceptional scientific relevance and technical excellence.
For ARRAKIHS
This achievement represents a decisive step. The mission’s observational program will soon deliver unprecedented images of the faint outskirts of nearby galaxies. Thanks to the HARKONENS simulations, we will have at our disposal a tailored theoretical framework capable of interpreting these observations and translating them into insight about galaxy formation, stellar halos, and the nature of dark matter.
We warmly congratulate Santi, Corentin, and all members of the COS team involved in securing this significant award. As ARRAKIHS moves closer to launch, the theoretical foundation that will accompany the mission is already taking shape and HARKONENS will play a central role in it.
