Magnetized accretion-ejection structures V. Effects of entropy generation inside the disc

TL;DR

This paper introduces an energy equation accounting for entropy generation in magnetized accretion discs, revealing thermal effects significantly enhance jet ejection efficiency and enable diverse jet velocities.

Contribution

It is the first to include entropy generation effects in steady-state MHD models of accretion discs driving jets, showing thermal effects greatly influence jet launching capabilities.

Findings

Thermal effects increase jet ejection efficiency from 0.01 to 0.5.

Including entropy allows modeling both fast and slow magnetic rotators.

Jet properties depend critically on detailed disc energetics.

Abstract

In this paper, steady-state MHD calculations of non-relativistic magnetized accretion discs driving jets are presented. For the first time, an energy equation describing the effects of entropy generation along streamlines is included. Using a simplified approach, we showed that thermal effects have a tremendous influence on the disc capability to feed jets with mass. The disc ejection efficiency is measured by the parameter $\xi= d \ln \dot{M}_{a}/d \ln{r}$, where $ \dot{M}_{a}(r)$ is the local disc accretion rate. While previous self-similar solutions were only able to produce jets with $\xi \sim 0.01$, solutions with a coronal heating display huge efficiencies up to $\xi \sim 0.5$. Moreover, taking thermal effects into account allows to obtain both fast and slow magnetic rotators. Since most of the jet properties (like asymptotic velocity or degree of collimation) depend on the mass load, it arises from this study that any quantitative result requires a detailled analysis of the disc energetics.