Revealing dark matter with small-scales dynamics

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Since you started reading this, many millions of dark matter particles have gone through your body, at speeds of a few hundred miles per second. These particles are approximately four times more abundant than ordinary baryonic matter, yet their nature is still a puzzling mystery: my research is aimed to understand it.The internal dynamics of galaxies and galaxy clusters, as well as the large-scale structure of the universe point to the existence of a pervasive form of matter, which interacts through gravity, but is invisible to electromagnetic radiation. Several different models have been proposed during the past decades, but we still do not know what such a 'dark matter' actually consists of, or how it relates to the Standard Model of particle physics. We know that galaxies are embedded in massive dark matter haloes, and that dark matter has a fundamental role in all of the processes that govern the formation and evolution of the galaxies themselves. For instance, the particles that are going through you right now are part of our own galaxy, the Milky Way.The properties of dark matter particles can be constrained by studying the structure and dynamics of galaxies. After a long series of incremental advances, the coming decade will allow a number of breakthroughs in this field of research. Launched in December 2013, the Gaia satellite is currently measuring positions and velocities of billions of stars in the Milky Way, composing a full kinematic map of our galaxy of unprecedented size, extent and data quality. This map provides the instruments to revolutionise our understanding of how galaxies assemble through cosmic time and to finally test the predictions of different dark matter models. My research programme focuses on achieving both of these goals by exploiting Gaia data as well as data from a number of other upcoming dedicated major surveys.The dark matter halo of the Milky Way has assembled hierarchically by accreting and engulfing several tens of smaller satellite galaxies. The Gaia satellite will provide a full record of this process, mapping the streaming debris of each of these disrupted dwarf galaxies. Gaia data contains a wealth of kinematic substructures and phase-space overdensities, each composed of stars originating from a common progenitor, still moving on similar orbits to the present day. With this data we will be able to reconstruct how the Galaxy formed and evolved, an invaluable `Rosetta Stone' to decode how millions of other galaxies assembled, driven by dark matter's gravity.One of the crucial differences between competitive dark matter models is in the amount and properties of small-scale substructure in galaxy haloes. Gravitationally bound clumps of dark matter (subhalos) are abundant in the currently prevailing cold dark matter model, but much rarer or absent in a number of alternative models. Confirming or disproving the existence of subhaloes and measuring their abundance as a function of mass, pinpoints the dark matter power spectrum, and therefore the nature of the dark matter particle. Subhaloes are invisible, but can perturb the motion of the stars they happen to fly by to, through their gravity. The thin stellar streams formed by disrupting Globular Clusters are the best available 'dynamical dark matter detectors'. For the first time, the kinematic map provided by Gaia will have the precision necessary to detect these perturbations. Dark matter has been a mystery for many decades, it is very exciting that so much progress is now possible within ten years.