BEYOND-STANDARD-DISK

Beyond the Standard Accretion Disk Model: Theoretical Foundations and Observational Implications

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 Obiettivo del progetto (Objective)

'Most celestial bodies, ranging from planets to stars to black holes, gain mass during their lives by gravitationally attracting matter from their environments. This accretion process takes place via a disk-like structure around the gravitating object. Understanding the physical processes that determine the rate at which matter accretes and energy is radiated in these disks is vital for unraveling the formation, evolution, and fate of almost every type of object in the Universe. Despite the fact that magnetic fields have been known to play a fundamental role in accretion disks since the early 90’s, the majority of astrophysical questions that depend on the details of how disk accretion proceeds are still being addressed using the ’standard’ accretion disk model (developed in the early 70’s), where magnetic fields do not appear explicitly. This has produced a profound disconnect between observations, usually interpreted with the standard paradigm, and modern accretion disk theory and numerical simulations, where magnetic turbulence is crucial. The aim of my project is to develop what will become the new standard approach to accretion disks in astrophysics. The first part of the proposal addresses accretion disk physics and magnetized turbulence. I will build on my previous work with the goal of developing the theoretical framework that will incorporate magnetic fields into self-consistent disk models. The second part of the proposal concerns the dynamics of magnetic fields and related transport processes in the low-density regions of accretion disks, where the observed non-thermal radiation originates. By using a kinetic particle description of the plasma, I will be able to self-consistently calculate the non-thermal radiation spectra resulting from particle acceleration in the turbulent disk coronae. The proposed approach will allow us to address the most fundamental problems in modern astrophysics in a way that has no counterpart within the standard framework.'

Introduzione (Teaser)

New models of how stars and black holes acquire their mass are redefining our understanding of these fundamental processes in astrophysics.

Descrizione progetto (Article)

Astrophysicists are striving to unravel the mechanisms behind the formation and evolution of celestial bodies, such as stars and black holes. These objects gain mass by gravitationally attracting matter from their environments. This fascinating process, known as accretion, usually involves a disk-like structure around the celestial body. Understanding how these disks work could provide the answer to many questions in astrophysics.

The EU-funded project 'Beyond the standard accretion disk model: Theoretical foundations and observational implications' (BEYOND-STANDARD-DISK) has developed more accurate models for the processes governing accretion disk.

Building on previous work in the field, the project team aimed to develop a theoretical framework that incorporates magnetic fields into self-consistent disk models. It looked at how magnetic fields influence the turbulence that enables matter in accretion disks to spiral towards the central objects. Through numerical simulations and mathematical calculations, the project team made progress in several areas towards understanding the dynamics of magnetic fields in accretion disks around stars and black holes.

Another main objective of the project involved studying the transport processes in the low-density regions of accretion disks where the observed non-thermal radiation originates. In this respect, the team investigated plasma dynamics at the kinetic level in collaboration with the Computational Astrophysics Group at the Niels Bohr Institute of the University of Copenhagen, Denmark. Building on these ideas, the team also conducted breakthrough studies on the subject of dilute plasmas by studying new aspects of the magnetothermal instability (MTI) and the heat-flux-buoyancy instability (HBI), that play a key role in galaxy clusters.

Armed with a powerful set of results, the team published several papers that have brought the scientific community closer to understanding the precise mechanics of accretion disks. Many fields in astrophysics will benefit from this research, providing new models and insight regarding accretion disks, planet formation and the impact of supermassive black holes on galaxy evolution. The high international profile of these subjects will enhance the European Research Area's (ERA) competitiveness in the fascinating interdisciplinary field of theoretical astrophysics.