Objective Giant galaxies like our own are surrounded by a large number of dwarf galaxy satellites that perform a complex orbital dance. Theoretical models predict that this dance should be composed of randomly oriented elliptical orbits, but Milky Way (MW) observations reveal the opposite: most satellites orbit in the same plane and have orbits that are more circular than expected. This discrepancy is a major problem that lacks an answer. It could signal a fundamental breakdown of the current cosmological model or, alternatively, that the MW is very atypical, a 1 in 1000 system. Studies of satellite orbits cannot yet be carried out for other galaxies, so the only option is to examine the MW in more detail. My proposed research will deliver ground-breaking new insights into the anomalous dynamics of satellites, and, through this, uncover the formation history of our galaxy. First, I will investigate the phenomena that give rise to the atypical orbits of the MW satellites. Two key drivers are the accretion of satellites along cosmic web filaments and the geometry of the dark matter halo of the central galaxy. Secondly, using state-of-the-art galaxy formation models, I will perform detailed simulations to predict the distribution of faint satellites and the stellar halo of our galaxy. These contain vital clues to the root cause of the anomalous satellite orbits problem. I will compare the model predictions to MW observations to make an unprecedented test of the current cosmological paradigm. The same simulations are essential to understand how representative are the MW satellites and stellar halo, and thus the extent to which they can be used to test the nature of dark matter and galaxy formation models.The proposed research combines my two areas of expertise, large scale structure and satellite galaxies, with the world-leading galaxy formation models and simulations of Prof. Schaye's group, and, together, they provide the ideal setting to make this project a major success. Fields of science humanitieshistory and archaeologyhistoryengineering and technologymechanical engineeringvehicle engineeringaerospace engineeringsatellite technologynatural sciencesphysical sciencesastronomyastrophysicsdark matternatural sciencesmathematicspure mathematicsgeometrynatural sciencesphysical sciencesastronomyphysical cosmologygalaxy evolution Programme(s) H2020-EU.1.3. - EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions Main Programme H2020-EU.1.3.2. - Nurturing excellence by means of cross-border and cross-sector mobility Topic(s) MSCA-IF-2017 - Individual Fellowships Call for proposal H2020-MSCA-IF-2017 See other projects for this call Funding Scheme MSCA-IF-EF-ST - Standard EF Coordinator UNIVERSITEIT LEIDEN Net EU contribution € 177 598,80 Address RAPENBURG 70 2311 EZ Leiden Netherlands See on map Region West-Nederland Zuid-Holland Agglomeratie Leiden en Bollenstreek Activity type Higher or Secondary Education Establishments Links Contact the organisation Opens in new window Website Opens in new window Participation in EU R&I programmes Opens in new window HORIZON collaboration network Opens in new window Total cost € 177 598,80