A measurement of the electromagnetic luminosity of a Kerr black hole

Jonathan C. McKinney, Charles F. Gammie

Research output: Contribution to journalArticlepeer-review


Some active galactic nuclei, microquasars, and gamma-ray bursts may be powered by the electromagnetic braking of a rapidly rotating black hole. We investigate this possibility via axisymmetric numerical simulations of a black hole surrounded by a magnetized plasma. The plasma is described by the equations of general relativistic magnetohydrodynamics, and the effects of radiation are neglected. The evolution is followed for 2000GM/c3, and the computational domain extends from inside the event horizon to typically 40GM/c2. We compare our results to two analytic steady state models, including the force-free magnetosphere of Blandford & Znajek. Along the way we present a self-contained rederivation of the Blandford-Znajek model in Kerr-Schild (horizon penetrating) coordinates. We find that (1) low-density polar regions of the numerical models agree well with the Blandford-Znajek model, (2) many of our models have an outward Poynting flux on the horizon in the Kerr-Schild frame, (3) none of our models have a net outward energy flux on the horizon, and (4) one of our models, in which the initial disk has net magnetic flux, shows a net outward angular momentum flux on the horizon. We conclude with a discussion of the limitations of our model, astrophysical implications, and problems to be addressed by future numerical experiments.

Original languageEnglish (US)
Pages (from-to)977-995
Number of pages19
JournalAstrophysical Journal
Issue number2 I
StatePublished - Aug 20 2004


  • Accretion, accretion disks
  • Black hole physics
  • Galaxies: active
  • Hydrodynamics
  • Turbulence

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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