Variability of the inner dead zone edge in 2D radiation hydrodynamic simulations

Context. The inner regions of protoplanetary discs are prone to thermal instability (TI), which can significantly impact the thermal and dynamical evolution of planet-forming regions. Observable as episodic accretion outbursts, such periodic disturbances shape the disc’s vertical and radial structure.Aims. We have investigated the stability of the inner disc edge around a Class II T Tauri star and analysed the consequences of TI on the thermal and dynamic evolution in both the vertical and radial dimensions. A particular focus is laid on the emergence and destruction of solid-trapping pressure maxima.Methods. We conducted 2D axisymmetric radiation hydrodynamic simulations of the inner disc in a radial range of 0.05 AU to 10 AU. The models include a highly turbulent inner region, the transition to the dead zone, heating by both stellar irradiation and viscous dissipation, vertical and radial radiative transport, and tracking of the dust-to-gas mass ratio at every location. The simulated time frames include both the TI phase and the quiescent phase between TI cycles. We tracked the TI on S-curves of thermal stability.Results. Thermal instability can develop in discs with accretion rates of ≥3.6 ⋅ 10^{−9 M_{⊙ yr−1 and results from the activation of mag-netorotational instability (MRI) in the dead zone after the accumulation of material beyond the MRI transition. The TI creates an extensive MRI active region around the midplane and disrupts the stable pebble and migration trap at the inner edge of the dead zone. Our simulations consistently show the occurrence of TI reflares that, together with the initial TI, produce pressure maxima in the inner disc within 1 AU, possibly providing favourable conditions for streaming instability. During the TI phase, the dust content in the ignited regions adapts itself in order to create a new thermal equilibrium manifested in the upper branch of the S-curve. In these instances, we find a simple relation between the gas and dust-surface densities.Conclusions. On a timescale of a few thousand years, TI regularly disrupts the radial and vertical structure of the disc within 1 AU. While several pressure maxima are created, stable migration traps are destroyed and reinstated after the TI phase. Our models provide a foundation for more detailed investigations into phenomena such as the short-term variability of accretion rates.}}