HALLDISCS · Hall dominated turbulence in protoplanetary discs
FP7 — People (Marie Curie Actions)
- Duration
- 2012-01-01 → 2014-12-31
- EU contribution
- €75,000
- Participants
- 1
- Scheme
- MC-CIG
Lines connect the coordinator with its partners.
Results in brief
Hall dominated turbulence in protoplanetary discs
Protoplanetary discs are poorly ionised due to their low temperatures and high column densities, and are therefore subject to three "non-ideal" magnetohydrodynamic effects: Ohmic dissipation, ambipolar diffusion, and the Hall effect. The existence of magnetically driven turbulence in these discs has been a central question since the discovery of the magnetorotational instability. Early models considered Ohmic diffusion only and led to a scenario of layered accretion, in which a magnetically "dead" zone in the disc midplane is embedded within magnetically "active" surface layers at distances ~1-10 au from the central protostellar object. Recent work has suggested that a combination of Ohmic dissipation and ambipolar diffusion can render both the midplane and surface layers of the disc inactive and that torques due to magnetically driven outflows are required to explain the observed accretion rates. The HallDiscs project reassess this picture by performing three-dimensional numerical simulations that include, for the first time, all three non-ideal MHD effects. The main finding of this project is that Hall effect can generically "revive" dead zones by producing a dominant azimuthal magnetic field and a large-scale Maxwell stress throughout the midplane. We have moreover demonstrated the possibility of generating self-organising structures such as large scale zonal flows, which possibly have observable counterparts like ring-like structures. These results have dramatic consequences on our understanding of protoplanetary disc dynamics and planet formation process. In particular, they provide a natural framework explaining the recent observations of ring like structures in protoplanetary discs, without needing planets.
Data: CORDIS, © European Union
Project objective
The goal of this project is to obtain a global and precise description of turbulence in protoplanetary discs.Protoplanetary discs are made of gas and dust orbiting around a young star. Among other things, we think discs are the birth place of planets. From the lifetime of these objects, we know that protoplanetary discs are accreting, i.e. matter is slowly ``falling'' on the central star. However, in order to explain the accretion of matter, astrophysicists have to assume that discs are turbulent. The way turbulence is sustained in these objects is still strongly debated. However, the magnetorotational instability is one of the most promising candidates to explain the anomalous transport observed in discs. The plasma in protoplanetary discs is known to be weakly ionised. Detailed calculations have shown that in such plasmas, a nonideal MHD effect known as the Hall effect should be dominant.The HallDiscs project will tackle the complex problem of MHD turbulence in a realistic model of accretion disc dominated by the Hall effect. It will in particular evaluate the importance of the Hall effect in the nonlinear regime of the MRI, where developed turbulence is found. This is of particular importance as this nonideal MHD effect can create new instabilities which could dramatically modify our vision of protoplanetary discs turbulence. This proposal relies on the use of a very efficient and highly accurate spectral MHD code to perform Hall-MHD numerical simulations. The HallDiscs project will provide unprecedented constrains on the properties of MHD turbulence in discs, the conditions associated with jet launching from discs and the initial stages of planet formation. Furthermore, this project offers a unique opportunity to bring back to IPAG the expertise in numerical MHD I have gained during my postdoctoral experience in Cambridge.
Original text from CORDIS.
Participants
- CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE CNRS · ParisCoordinatorFrance
Links
Data: CORDIS, © European Union