Luminous quasars powered by accreting supermassive black holes (SMBHs) have been found in the early universe at z≳ 7.5, which set a strong constraint on both the seed black hole (BH) mass and the rapid growth of the SMBHs. In this work, we explore how the SMBHs grow 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, therefore the mass-accretion rate of the 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≳ 7 may be grown through chaotic accretion predominantly driven by magnetic outflows from a stellar mass BH, when the disks are radiating at moderate luminosity (∼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.
The Astrophysical Journal
- Pub Date:
- December 2019
- Magnetic fields;
- Supermassive black holes;
- Astrophysics - High Energy Astrophysical Phenomena
- 14 pages, 7 figures, 1 table, accepted for publication in ApJ