Launching and Quenching of Black Hole Relativistic Jets at Low Accretion Rate

TL;DR

This paper proposes a new MHD-based paradigm explaining how black hole jets are launched and quenched depending on accretion rates and disk types, aligning with observed BH disk-jet coupling phenomena.

Contribution

It introduces a magnetohydrodynamical model for BH jet launching and quenching based on accretion disk types and plasma effects, advancing understanding of BH jet physics.

Findings

Jet launching occurs with an outer SSD and inner advection-dominated flow.

Jet quenching happens when the entire disk becomes an SSD.

The model explains observed radio and X-ray luminosity correlations.

Abstract

Relativistic jets are launched from black hole (BH) X-ray binaries and active galactic nuclei when the disk accretion rate is below a certain limit (i.e., when the ratio of the accretion rate to the Eddingtion accretion rate, $\dot{m}$, is below about 0.01) but quenched when above. We propose a new paradigm to explain this observed coupling between the jet and the accretion disk by investigating the extraction of the rotational energy of a BH when it is surrounded by different types of accretion disk. At low accretion rates (e.g., when $\dot{m}\lesssim0.1$), the accretion near the event horizon is quasi-spherical. The accreting plasmas fall onto the event horizon in a wide range of latitudes, breaking down the force-free approximation near the horizon. To incorporate the plasma inertia effect, we consider the magnetohydrodynamical (MHD) extraction of the rotational energy from BHs by the accreting MHD fluid, as described by the MHD Penrose process. It is found that the energy extraction operates, and hence a relativistic jet is launched, preferentially when the accretion disk consists of an outer Shakura-Sunyaev disk (SSD) and an inner advection-dominated accretion flow. When the entire accretion disk type changes into an SSD, the jet is quenched because the plasmas brings more rest-mass energy than what is extracted from the hole electromagnetically to stop the extraction. Several other observed BH disk-jet couplings, such as why the radio luminosity increases with increasing X-ray luminosity until the radio emission drops, are also explained.