SESS

Galaxies are unique laboratories to test the universal law of gravity, the driving force from their outskirts (the galactic disc) up to their inner cores (the galactic nucleus). Numerous observational, computational, and theoretical efforts have recently been devoted to understanding, modelling and explaining galaxies’ cosmic evo- lution. Indeed, (i) new instruments such as Gaia and Gravity provide a wealth of information on the dynamical state of our Galaxy, past and present; (ii) recent theoretical breakthroughs in our understanding of the statistical kinetic theory of self-gravitating systems (e.g., the Balescu-Lenard equation) are now mature enough to follow, for the first time, the lasting effects of long-range coupled gravitationally-amplified perturbations on the orbital structure of self-gravitating systems. SESS will benefit from these joint developments to explore the long-term evolution of galaxies embedded in their cosmic environment. Leveraging the fact that all these systems can be described by the same extended framework as gravity governs them all, SESS will tackle galactic evolution in a truly novel way, compared to state-of-the-art methods such as direct numerical simulations. By adopting techniques from stochastic theory, by treating processes statistically, and by capturing the astrophysical differences at each galactic scale, SESS will offer unique and unprecedented physical insights into the competing dynamical processes at play. For that purpose, SESS will generalise and tailor the kinetic theory of self-gravitating systems to describe their long- term dynamics. SESS will also implement these new secular formalisms to characterise long-term astrophysical evolutions. Through this unconventional and interdisciplinary approach, SESS will offer in particular novel clues on the long-term orbital reshuffling of stars orbiting a supermassive black hole in a galactic nucleus, as well as on the intricate dynamics of globular clusters and galactic discs.