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Horizon 2020 - ERC Starting Grant

"First-principles global MHD disc simulations: Defining planet-forming environments in early solar systems"

The aim of my research project is to create the most realistic computer simulations of protoplanetary discs of gas and dust, thus defining the environment that shapes the early development of planetary systems.

Project overview

In their role as planet nurseries, protoplanetary discs are of key interest to planet formation theory. Their dynamical, radiative and thermodynamic properties critically define the environment for embedded solids: dust grains, pebbles and planetesimals. In short, the building blocks of planet formation. The discs' dynamics and structure in turn depend critically on the influence of magnetic fields that couple to tenuously ionised and low-density regions. Being comparatively cold and dense, the ionisation state of the disc plasma is dominated by external far-UV, X-Ray, and cosmic-ray radiation, leading to a layered vertical structure - with turbulent, magnetised surface layers and a magnetically-decoupled midplane. This classic dead-zone picture is now turned upside-down by previously ignored micro-physical effects.

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Scientific Results

Protoplanetary disks accrete onto their central T Tauri star via magnetic stresses. When the effect of ambipolar diffusion is included, and in the presence of a vertical magnetic field, the disk remains laminar in its planet-forming inner region, and a magnetocentrifugal disk wind forms that provides an important mechanism for removing angular momentum. We have performed global MHD simulations where the time-dependent gas-phase electron and ion fractions are computed under FUV and X-ray ionization with a simplified recombination chemistry.

Radiative-magnetic wind model: Detail from a proof-of-concept global MHD simulation of a PPD with ambipolar diffusion, radiative transfer and stellar irradiation, showing the magnetic field strength (colour), velocity arrows (black) and magnetic field lines (white), and iso-contours of the radiation temperature (grey).

To investigate whether the mass loading of the wind is potentially affected by the limited vertical extent of our existing simulations, we attempt to develop a model of a realistic disk atmosphere. To this end, by accounting for stellar irradiation and diffuse reprocessing of radiation, we aim at improving our models towards more realistic thermodynamic properties.

related publications

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This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No 638596).