Is the energy generation rate of nuclear reactions in hot accretion flows important?

TL;DR

This paper assesses whether nuclear reaction energy generation significantly impacts hot accretion flows around black holes, concluding it is negligible compared to viscous heating, thus simplifying modeling assumptions.

Contribution

It provides the first quantitative comparison showing nuclear reaction heating is negligible in hot accretion flows around black holes.

Findings

Nuclear reaction heating is at most 1% of viscous heating.

Nuclear reactions do not significantly affect accretion flow dynamics.

Standard models can ignore nuclear heating without loss of accuracy.

Abstract

The temperature of hot accretion flows around black holes is sufficiently high for the ignition of nuclear reactions. This is potentially an important nucleosynthesis mechanism in the universe. As the first step in studying this problem, we need to measure physical quantities such as density and temperature of the accretion flow. In usual studies of the hot accretion flow, viscous dissipation is considered to be the only heating mechanism, while the heating caused by nuclear reactions is not considered. In this paper, we investigate whether the energy generation rate of nuclear reaction is important compared to the viscous heating. Our calculation indicates that the former is at most one percent of the latter and thus is not important. The dynamics of accretion flow can be therefore calculated in the usual way, without the need to consider heating due to nuclear reactions.