Preparations have already begun at the Observatorio Astrofísico de Javalambre (OAJ) to install a replica of the binocular telescope that will be launched into space with the ARRAKIHS mission (Analysis of Resolved Remnants of Accreted galaxies as a Key Instrument for Halo Surveys). The instrumentation will be ready before the end of the year and will be an essential part of CEFCA's collaboration with the first European Space Agency mission led by Spain.

The ARRAKIHS mission includes more than 90 researchers and technologists from 22 research centres and universities in Switzerland, Sweden, Austria, Belgium, Portugal, Norway, the United Kingdom, the United States, Taiwan and Thailand. The consortium also includes Spanish and European aerospace companies.

Simply put, the mission will observe 80 nearby galaxies similar to our own Milky Way at unprecedented depth. Specifically, the mission's challenge is to detect the light from objects with surface brightness 10,000 times fainter than the darkest areas we see in the night sky. To do this, a satellite will be launched and orbit the Earth at an altitude of 800 kilometres.

The contribution of the Centro de Estudios de Física del Cosmos de Aragón (CEFCA) will be threefold: scientific, with researchers working on the scientific analysis of the data; technical, leading the development of the software that will process and analyse the data; and practical, with observations from the OAJ with a binocular telescope very similar to the one that will be launched into space. The latter contribution will be launched in a few weeks.

Before the end of the year, this double telescope, known as the Earth Demonstrator of the space mission, will be integrated into the OAJ's monitor building and will carry out observations for at least two years. The mount on which the binoculars will be mounted, as well as the other auxiliary equipment necessary for their operation and control, is already in place in the building.

Each of the two binoculars to be launched will consist of two telescopes (150 mm diameter), the design of which has been successfully validated in space, both on the International Space Station and on board microsatellites. An optimised version of this equipment will be used in this initial phase. It is intended to demonstrate its imaging quality and refine both the observational strategy and the image processing routines and codes with a team led by Dr. Antonio Marín-Franch from CEFCA. The ARRAKIHS mission was born 13 years ago and competed alongside 19 other proposals from European consortia in a competitive project to be finally selected as mission F (Fast). The question is ‘What is dark matter?’ and the space mission aims to answer it.

According to the standard cosmological model, objects of lower mass (so-called dwarf galaxies) should be observed around any galaxy, whose components are swallowed up by the central massive galaxy. In the process, so-called tidal stellar streams are formed, composed of the stars that are torn away from these dwarf galaxies. These trails orbit in the halo of massive galaxies, such as our Milky Way, as they are torn apart by gravitational interaction.

The aim of this space mission is to test this cosmological model and try to detect stellar trails that have so far proved elusive. The reason for this is the discrepancy between the number of dwarf galaxies and tidal streams that are detected and those that are predicted to be present: the simulations predict a higher abundance than observed. Is the model or the instruments with which they have been observed so far at fault?

To resolve this discrepancy, ARRAKIHS aims to observe the closest galaxies similar to our own from space at a depth unprecedented to date. The technical and scientific team of CEFCA, recognised at European level for its ability to detect objects with very low surface brightness, is key to this. The mission will place the satellite 800 kilometres from the Earth and thus avoid atmospheric contamination. The objective is deep observation, 10 000 times more than the darkest point in the sky as seen from Earth. According to the latest studies, at this level at least one tidal stream should be detected in each of the 80 massive galaxies to be observed.

The Spanish representatives of the mission are led by Dr. Rafael Guzmán (Instituto de Física de Cantabria, IFCA) in collaboration with researchers from IFCA, the Instituto de Ciencias del Espacio (ICE), the Universidad Complutense de Madrid (UCM), the Centro de Estudios de Física del Cosmos de Aragón (CEFCA), the Instituto de Astrofísica de Andalucía (IAA), the Instituto de Astrofísica de Canarias (IAC) and the Centro de Astrobiología (CAB).