Two Types of Ergospheric Jets from Accreting Black Holes: The Dichotomy of Fanaroff-Riley Galaxies

TL;DR

This paper explores how different accretion environments around black holes produce two distinct types of relativistic jets, explaining the Fanaroff-Riley galaxy classification through jet formation mechanisms.

Contribution

It identifies the link between accretion disk structure and jet properties, proposing a dichotomy in jet types based on accretion rate and disk geometry.

Findings

Moderate accretion rates produce jets with moderate luminosity and speed (FR I galaxies).

Higher accretion rates lead to more powerful, faster jets (FR II galaxies).

Jet formation mechanisms differ: magnetohydrodynamic Penrose process vs. Blandford-Znajek process.

Abstract

We investigate the extraction of the rotational energy of a black hole under different accreting environment. When the accretion rate is moderate, the accretion disk consists of an outer thin disk and an inner advection-dominated accretion flow. In such a combined disk, the outer thin disk can sustain a magnetic field with moderate strength at the event horizon, leading to the formation of relativistic jets with moderate luminosity and speed via the magnetohrodynamic Penrose process. When the accretion rate increases enough, on the other hand, the disk becomes geometrically thin near the horizon. In this slim disk, the denser plasmas can sustain a stronger magnetic field than that in a combined disk, leading to the formation of jets with greater luminosity and speed via the Blandford-Znajek processs. It is discussed that the former jets are associated with the Fanaroff-Riley (FR) I galaxies and the latter with FR II galaxies.