The formation of free floating planets from massive self-gravitating discs with growing binary seeds

Over the past 25 years, observations have uncovered a large population of freefloating planets (FFPs), whose origins remain debated. Massive FFPs (several Jupiter masses or more) may form via gravitational collapse of molecular clouds, similar to stars. Lower-mass FFPs likely originate in planetary systems and are later ejected through dynamical interactions. In this thesis, I show that disc fragmentation in young stellar binaries is an efficient source of Jupiter-like FFPs (JFFPs). In this model, disc fragmentation at tens to 100 au from the primary star produces gas giants, while fragmentation further out forms a more massive object that eventually evolves into a secondary star. I present 3D simulations of massive, self-gravitating discs with embedded Jupiter-mass planets and a secondary seed (5 – 50 MJ); chaotic migration leads to frequent planet–secondary interactions, imparting velocity kicks to the planets that can result in planet ejections. The ejection fraction increases steeply with the secondary-to-primary mass ratio, q, reaching 2/3 for qs ě 0.05. Compared to Core Accretion JFFPs, disc fragmentation JFFPs: (i) form earlier, and may be more abundant in young clusters, and (ii) are ejected at much lower velocities. This model is also expanded to include varying initial inclinations for the planets (0 – 90°), and masses (0.001 – 3 MJ), while keeping the initial secondary mass consistent throughout, at 25 MJ. The initial inclination of the planets does not appear to affect the ejection fraction, or the post-ejection velocities of FFPs. Interactions with the secondary can lead to ejections, regardless of planet mass – planets likely to be ejected are the ones that spend the most time in the vicinity of the secondary. Gravitationally unstable systems are therefore a promising mechanism for the production of FFPs.