ARRAKIHS: A new light on dark matter
The ARRAKIHS Mission
ARRAKIHS (Analysis of Resolved Remnants of Accreted galaxies as a Key Instrument for Halo Surveys) is a cutting-edge mission of the European Space Agency (ESA) proposed by the ARRAKIHS Mission Consortium to investigate the nature of dark matter and galaxy formation on small scales. Selected as an F-mission (fast mission) in November 2022, it is currently in phases O/A/B, with an adoption decision expected in mid-2026.
ARRAKIHS is designed to explore how well the Λ-Cold Dark Matter (ΛCDM) model aligns with observations of smaller-scale structures, such as galaxy halos. One of its main goals is to investigate potential mismatches between what the model predicts, and what we observe in the real world. In particular, the mission aims to determine whether these mismatches point to the need for alternative dark matter models or refinements to baryonic physics in galaxy formation simulations.
ARRAKIHS will conduct deep simultaneous visible and infrared imaging of a statistically representative sample of nearby halos of Milky Way-type galaxies in the local Universe, reaching unprecedented low surface brightness levels. ARRAKIHS will provide key tests with statistical significance to determine whether the reported tensions arise from selection effects or small number statistics. However, if these tensions are confirmed, ARRAKIHS will highlight inconsistencies in the current theoretical models of MW-like galaxy formation, highlighting the need for refinements or alternative frameworks.
The ARRAKIHS mission has three primary observational goals: to provide robust statistics on the numbers and shapes of tidal stellar structures, characterise the shape and extent of the diffuse stellar halo, and determine the abundance and locations of satellite galaxies across a comprehensive sample of MW-like galaxies beyond the Local Group.
ARRAKIHS at UZH
Swiss coordinator: Prof. Ben Moore (Dept. of Astrophysics)
Theoretical cosmology: Prof. Robert Feldmann (Dept. of Astrophysics)