Simultaneous gas accretion onto a pair of giant planets: Impact on their final mass and on the protoplanetary disk structure

Several planetary systems are known to host multiple giant planets. However, when two giant planets are accreting from the same disk, it is unclear what effect the presence of the second planet has on the gas accretion process of both planets. In this paper we perform long-term 2D isothermal hydrodynamical simulations (over more than 0.5 Myrs) with the FARGO-2D1D code, considering two non-migrating planets accreting from the same gaseous disk. We find that the evolution of the planets' mass ratio depends on gap formation. However, in all cases, when the planets start accreting at the same time, they end up with very similar masses (0.9 $<m_{p,out}/m_{p,in}<$ 1.1 after 0.5 Myrs). Delaying the onset of accretion of one planet allows the planets' mass ratio to reach larger values initially, but they quickly converge to similar masses afterward (0.8 $<m_{p,out}/m_{p,in}<$ 2 in $10^5$ yrs). In order to reproduce the more diverse observed mass ratios of exoplanets, the planets must start accreting gas at different times, and their accretion must be stopped quickly after the beginning of runaway gas accretion (less than 0.5 Myrs), for example via disk dispersal. The evolution of the planets' mass ratio can have an important impact on the dynamics of the system and may constrain the formation history of Jupiter and Saturn.