Slim accretion disks around black holes

TL;DR

This thesis develops hydrodynamical models of slim accretion disks around black holes, extending standard thin disk models to high accretion rates, and explores their properties, stability, and astrophysical applications.

Contribution

It introduces a comprehensive numerical framework for slim disk models, including non-stationary and vertically-structured solutions, and applies these models to black hole spin estimation and accretion dynamics.

Findings

Slim disks can model high-luminosity accretion flows.

Vertical structure coupling improves model accuracy.

Applications include black hole spin measurement and super-critical accretion effects.

Abstract

In this thesis, I study hydrodynamical models of slim accretion disks --- advective, optically thick disks which generalize the standard models of radiatively efficient thin disks to all accretion rates. I start with a general introduction to the theory of accretion onto compact objects. It is followed by a derivation of the commonly-used standard models of thin disks. In the subsequent section I introduce the equations describing slim disks, explain the numerical methods I used to solve them and discuss properties of such solutions. I also give a general derivation of non-stationary equations and present the time evolution of thermally unstable accretion disks. I introduce a state-of-the-art approach coupling the radial and vertical structures of an advective accretion disk and discuss the improvements it brings to vertically-averaged solutions. I also present a numerical model of self-illuminated slim accretion disks. Finally, I present and discuss applications of slim accretion disks: estimating of spin of the central black hole in LMC X-3 through X-ray continuum fitting basing on high-luminosity data, spinning-up of black holes by super-critical accretion flows and normalizing of magnetohydrodynamical global simulations.