High-resolution simulations of disc tearing in the GW Orionis triple system

ABSTRACT The disc around the pre-main-sequence triple star system GW Orionis is known from observations to be warped and broken. Theoretical modelling has produced conflicting results regarding the mechanism responsible for breaking the disc. Analytical predictions for the measured parameters of GW Ori suggest the disc is only marginally stable to tearing. We present new high-resolution simulations of GW Ori that replicate the wavelike regime expected in thick, low-turbulence protoplanetary discs for the first time to settle this question. Using the most optimistic values of misalignment and stellar mass ratio allowed by observational constraints, we find that the GW Ori disc can be torn by stellar torques alone, without need for an embedded planet. Even if the disc retains a smooth warp in simulations with similar parameters, it is likely that any small perturbation in the density or temperature structure could cause the disc to break. The new simulations rule out retrograde disc rotation relative to the stellar orbits and tentatively suggest the thicker ($h/r = 0.04$) disc better matches observations. Going forward, we should take care to ensure models of GW Ori and similar systems appropriately represent the propagation of warps. Additionally, analytical predictions are derived from idealized (and often massless) discs and it is useful to assess how each observed disc might deviate from those assumptions, especially in the context of a young and active star-forming neighbourhood.