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1st-principles-discs Report Summary

Project ID: 306614
Funded under: FP7-IDEAS-ERC
Country: Denmark

Final Report Summary - 1ST-PRINCIPLES-DISCS (A First Principles Approach to Accretion Discs)

The ERC project 1st-principles-discs was devoted to advance our understanding of fundamental physical processes at work in accretion disks, which play a vital role in the formation and evolution of a wide range of astrophysical systems, including planets, stars, and black holes. The majority of astrophysical questions that depend on the details of how disk accretion proceeds are still being addressed using the “standard” paradigm developed in the early 70’s, where magnetic fields (known to play a fundamental role since the early 90’s) do not appear explicitly. This project aimed at going beyond the state-of-the-art by 1) Deepening our understanding of magnetohydrodynamic turbulence and its related transport properties in disks and 2) Investigating kinetic processes in hot, dilute regions of the accretion disk where the magnetohydrodynamic approximation breaks down. This ERC project enabled substantial progress in both of these endeavors, which are illustrated by the following research highlights: (i) We developed a new way to characterize magnetohydrodynamic turbulence in accretion disks; (ii) We extended the shearing-box framework to model non-barotropic disks in domains that are radially local, but vertically global; (iii) We established new links between dynamo theory and turbulence driven by the magnetorotational instability; (iv) We showed that turbulence in disks can be sustained at low magnetic Prandtl numbers; (v) We provided new insights on the global structure and transport processes in turbulent magnetized accretion disks; (vi) We developed a new particle-in-cell (PIC) Vlasov-fluid hybrid code in which the ions are considered as particles but the electrons (which are much lighter and therefore have less inertia) can be approximated as a fluid; (vii) We have developed a new integration scheme that enables the exact integration of the background shear flow, and employs shearing periodic boundary conditions, resulting in a fast and accurate algorithm to simulate the local dynamics of collisionless accretion disks. All in all, the project has significantly advanced our understanding of several fundamental problems in the context of astrophysical disks, leading to more than 15 peer-reviewed papers in high-impact international journals.

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