title: The long-term dynamical evolution of planetary-mass objects in star clusters
Creators: name: Flammini Dotti, Francesco
Publisher: name: University of Liverpool Repository
Year: 2023

description: The search for exo-planetary systems has seen tremendous progress in recent decades, and has resulted in astounding discoveries. From the discovery of the first confirmed exoplanet orbiting around a main sequence star in 1995, astronomers have attempted to measure and explain the characteristics of exo-planetary systems. Due to observational constraints, most of the discovered planetary systems were detected orbiting nearby field stars. To fully understand the formation and early evolution of planetary systems, it is necessary to study planetary systems in dense stellar environment, the birth places of stars. In these environments, gravitational interactions with neighbouring stars can substantially a↵ect the architecture of planetary systems. Most stars, perhaps all stars in the Galaxy, formed in crowded environments. These stellar aggregates typically dissolve within ten million years, while others remain gravitationally bound for millions to billions of years in the open clusters or globular clusters that are present in our Milky Way today. It is now commonly accepted that a large fraction of stars in our Milky Way host planetary companions. To backtrack the origin and dynamical evolution of exoplanets, it is necessary to carefully study the e↵ects of the environments in which these planetary systems spent their youth, and that of the Galactic field, open clusters, or globular clusters, in which they may spend the remaining part of their lives. In this work we analyse how di↵erent environments a↵ect the dynamical evolution of planetary systems and free-floating planets. We analyse the e↵ect of the star cluster environment on the evolution of planetary systems, by varying the initial stellar density of the star cluster, by studying the influence of an intermediate-mass black hole (IMBH) in the cluster centre, and by varying other star cluster properties (e.g., global rotation and virial ratio). We focus on the evolution of multi-planet planetary systems, rogue planets (i.e., planets not gravitationally bound to a star) and single- planet systems with a proto-planetary disk. We find that the star cluster environment can have a significant influence on the dynamics of planetary systems. Generally, the disruption rate of planetary systems is higher when (i) the star cluster is denser, (ii) when encountering stars have speeds comparable to the orbital speed of the planets, (iii) when the encounter is more impulsive (i.e., smaller distances between encountering stars and planets) and (iv) for encountering stars with near-parabolic trajectories. Planet- planet scattering, induced by encounters with neighbouring stars, plays a dominant role in shaping the evolution and final architecture of a multi-planet system. Disruption of planetary systems occurs more frequently in the presence of a IMBH, notably during the early phases of star cluster evolution (before the cluster fills its Roche lobe). The presence of a central IMBH enhances the ejection rate of stars and free-floating planets from the star cluster, while the presence of global rotation in the star cluster reduces the ejection rate of stars and free-floating planets from the star cluster.