Dynamical Structure of Viscous Accretion Disks with Shocks

TL;DR

This paper demonstrates that viscous ADAF accretion disks can contain isothermal shocks even with high viscous dissipation, expanding understanding of shock formation and its implications for jet power in black hole systems.

Contribution

It is the first to show that steady ADAF disks with shocks can exist at high viscosity levels, identifying the parameter space where shocks are possible.

Findings

Isothermal shocks can form in viscous ADAF disks at high viscosity levels.

The shock region disappears when viscosity exceeds a critical value (~0.27).

Shocks can provide sufficient energy to power relativistic jets in black hole systems.

Abstract

We develop and discuss global accretion solutions for viscous ADAF disks containing centrifugally supported isothermal shock waves. The fact that such shocks can exist at all in ADAF disks is a new result. Interestingly, we find that isothermal shocks can form even when the level of viscous dissipation is relatively high. In order to better understand this phenomenon, we explore all possible combinations of the fundamental flow parameters, such as specific energy, specific angular momentum, and viscosity, to obtain the complete family of global solutions. This procedure allows us to identify the region of the parameter space where isothermal shocks can exist in viscous ADAF disks. The allowed region is maximized in the inviscid case, and it shrinks as the level of viscous dissipation increases. Adopting the canonical value gamma=1.5 for the ratio of specific heats, we find that the shock region disappears completely when the Shakura-Sunyaev viscosity parameter alpha exceeds the critical value ~0.27. This establishes for the first time that steady ADAF disks containing shocks can exist even for relatively high levels of viscous dissipation. If an isothermal shock is present in the disk, it would have important implications for the acceleration of energetic particles that can escape to power the relativistic jets commonly observed around underfed, radio-loud black holes. In two specific applications, we confirm that the kinetic luminosity lost from the disk at the isothermal shock location is sufficient to power the observed relativistic outflows in M87 and Sgr A*.