A central question in astrophysics is how galaxies acquire their observed structures, shapes, and kinematic properties. My research addresses this problem by studying the gravitational evolution of self-gravitating systems far from equilibrium, with the goal of understanding the physical origin of galaxies and their substructures.
To investigate these processes, we have performed controlled numerical experiments in which isolated systems evolve from simple initial conditions under the action of gravity alone. This approach has allowed us to identify several fundamental mechanisms governing galaxy formation, including mass and energy ejection during gravitational collapse, the differences between cold and warm initial conditions, the origin of the universal properties of quasi-stationary states, the generation of angular momentum and triaxiality, the formation of satellite systems, and the effects of particle discreteness in numerical simulations.
A particularly important result of this work is the demonstration that complex galactic structures can emerge naturally from purely gravitational dynamics. Contrary to the common view that spiral arms, bars, and rings require long-term secular evolution or dissipative processes, we have shown that they can arise spontaneously during the violent relaxation of rotating, non-spherical systems. These structures are long-lived but intrinsically out of equilibrium, reflecting the dynamical history of the gravitational collapse rather than a final equilibrium configuration.
Our studies indicate that gravitational collapse can generate a rich variety of morphologies, including spiral arms, bars, rings, triaxial cores, and satellite systems. These structures are associated with coherent motions of matter and characteristic phase-space correlations that persist for times much longer than the dynamical timescale.
We have also investigated the role of dissipative processes by including a gaseous component capable of radiative cooling. These studies show that gas dynamics can enhance and sustain spiral structures generated during violent collapse. In this scenario, spiral arms arise as a natural consequence of collective gravitational dynamics and coherent gas motions, rather than through slow secular evolution. The resulting galaxies can exhibit thick and thin disk components and differ significantly from the standard picture in which galaxies form gradually within massive dark matter halos through hierarchical merging.
More broadly, this research explores galaxy formation as a problem in non-equilibrium statistical physics, emphasizing the role of gravitational dynamics, collective effects, and long-lived quasi-stationary states in shaping the observed structure of galaxies.
Francesco sylos labini 