Supervisors info:
Νεκτάριος Βλαχάκης, Καθηγητής, Τμήμα Φυσικής, ΕΚΠΑ
Summary:
In astrophysics, accretion discs play an important role in the evolution of many other structures. However, there is a plethora of unanswered questions regarding the physical processes that explain all acquired observations of discs and their related jets. In the present study, an attempt is made to invastigate the dynamics inside a magnetized accretion disc in a non-ideal magneto-hydrodynamic framework. At first, an observational and theoretical argument is introduced, in favor of the «disc wind» paradigm, where accretion and ejection are interdependent, thus the MAES paradigm is considered appropriate to describe the disc and jets. The theoretical framework of MAES is thoroughly presented, explaining why an accretion disc should be threaded by a large scale magnetic field. Additionally, the types of accretion discs are explored, along with the accretion and ejection processes in turbulent, quasi-Keplerian discs. Then, within the non-ideal MHD framework (diffusion of the magnetic field and viscosity are present), a complete system of PDEs is presented and simplified into a system of ODEs using a self-similar ansatz. The approach of the energy equation is being discussed as well as the differentiation of this work from other related works by considering adiabatic transport of plasma along the stream lines and not the magnetic field lines, as it is often assumed. The importance of critical points in the flow is explained and an extensive discussion is made regarding the initial values and the set of free disc parameters. Finally, the programs used in an attempt to integrate the acquired system of ODEs are adduced and explained.
Keywords:
Accretion Discs, Self-similarity, Magnetohydrodynamics, ideal MHD, non-ideal MHD
