The dark sector of the Universe : dark matter and dark energy

More than 95 % of the Universe's content is black or unknown, starting with 25 % made of exotic dark matter, and for the last twenty-five years we've known that the expansion is accelerating, due to dark energy, which accounts for 70 %. We'll review the possible candidates for these exotic particles, and even theories of modified gravity. Dark energy could just be a cosmological constant, but it could also be a fifth element or quintessence, evolving over time. The Euclid satellite, launched in July 2023 by the European Space Agency, will observe a large part of the sky, and identify more than ten billion galaxies at different epochs. It will use several tools, such as gravitational lenses, baryonic acoustic oscillations, the growth rate of structures, galaxy clusters and space-redshift distortions, to lift the veil on the dark sector of the Universe.