Growth of massive black holes at high-z via accretion predominantly driven by magnetic outflows

TL;DR

This paper proposes a model where magnetic outflows enable rapid growth of supermassive black holes in the early universe, explaining the existence of billion-solar-mass quasars at high redshift.

Contribution

It introduces a magnetic outflow-driven accretion mechanism that allows for efficient black hole growth at sub-Eddington luminosities, aligning with observations of early quasars.

Findings

SMBHs can grow from stellar mass via magnetic outflows and chaotic accretion.

Most SMBHs are predicted to have moderate spins, limiting radio jet production.

High-redshift SMBHs likely grew through moderate luminosity accretion with magnetic outflows.

Abstract

Luminous quasars powered by accreting supermassive black holes (SMBHs) have been found in the early Universe at $z \gtrsim 7.5$, which set a strong constraint on both the seed black hole mass and the rapid growth of the SMBHs. In this work, we explore how the SMBHs are grown through Eddington limited accretion driven predominantly by magnetic outflows. Most angular momentum and the released gravitational energy in the disk can be removed by magnetic outflows, and therefore the mass accretion rate of the black hole (BH) can be high even if the disk is radiating at sub-Eddington luminosity. It is found that the SMBH with several billion solar masses discovered at $z\gtrsim 7$ may probably be grown through chaotic accretion predominantly driven by magnetic outflows from a stellar mass BH, when the disks are radiating at moderate luminosity ($\sim 0.5$ Eddington luminosity) with mild outflows. We find that most SMBHs are spinning at moderate values of spin parameter $a_*$, which implies only a small fraction of quasars may have radio jets.