Spin, accretion, and the cosmological growth of supermassive black holes

Research output: Contribution to journalArticle

Abstract

If supermassive black holes (SMBHs) are the energy sources that power quasars and active galactic nuclei (AGNs), then QSO SDSS 1148+5251, the quasar with the highest redshift (ZQSO = 6.43), hosts an SMBH formed within ∼0.9 Gyr after the big bang. This requirement places constraints on the cosmological formation of SMBHs, believed to grow from smaller initial seeds by a combination of accretion and mergers. We focus on gas accretion onto seeds produced by the collapse of Population III stars at high redshift. We incorporate the results of recent relativistic, MHD simulations of disk accretion onto Kerr black holes to track the coupled evolution of the masses and spins of the holes. We allow for an additional amplification of ∼10 4 in the mass of a typical seed due to mergers, consistent with recent Monte Carlo simulations of hierarchical mergers of cold dark matter halos containing black hole seeds. We find that the growth of Population III black hole remnants to ∼109 M∼ by ZQSO ≳ 6.43 favors MHD accretion disks over standard thin disks. MHD disks tend to drive the holes to a submaximal equilibrium spin rate a/M ∼ 0.95 and radiation efficiency εM ∼0.2, while standard thin disks drive them to maximal spin (a/M = 1) and efficiency (εM = 0.42). This small difference in efficiency results in a huge difference in mass amplification by accretion at the Eddington limit. The MHD equilibrium efficiency is consistent with the observed ratio of the QSO plus AGN luminosity density to the local SMBH mass density. Our prototype analysis is designed to stimulate the incorporation of results from relativistic stellar collapse and MHD accretion simulations in future Monte Carlo simulations of hierarchical structure formation to better determine the cosmological role of SMBHs and their mass and spin distributions.

Original languageEnglish (US)
Pages (from-to)59-68
Number of pages10
JournalAstrophysical Journal
Volume620
Issue number1 I
DOIs
StatePublished - Feb 10 2005

Keywords

  • Accretion, accretion disks
  • Black hole physics
  • Cosmology: theory
  • MHD
  • Quasars: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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