Prograde and retrograde black holes: Whose jet is more powerful?

Alexander Tchekhovskoy*, Jonathan C. McKinney

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

128 Scopus citations


The outflow efficiency (η) from black hole (BH) accretion disc systems is known to depend upon both the BH spin (α) and the amount of large-scale magnetic flux threading the BH and disc. Semi-analytical flux-trapping models suggest retrograde BHs should trap much more large-scale magnetic flux near the BH leading to much higher η than for prograde BHs. We self-consistently determine the amount of large-scale magnetic flux trapped by rapidly spinning (a = -0.9 and 0.9) BHs using global 3D time-dependent non-radiative general relativistic magnetohydrodynamic simulations of thick (h/r ≈ 0.3-0.6) discs. We find that BH-trapped flux builds up until it is strong enough to disrupt the inner accretion disc. Contrary to prior flux-trapping models, which do not include the back-reaction of magnetic flux on the disc, our simulations show prograde BHs trap more magnetic flux, leading to about three times higher η than retrograde BHs for |a| = 0.9. Both spin orientations can produce highly efficient jets, η ~ 100 per cent, with increasing η for increasing disc thickness. The similarity of η for prograde and retrograde BHs makes it challenging to infer the sign of a based on jet energetics alone.

Original languageEnglish (US)
Pages (from-to)L55-L59
JournalMonthly Notices of the Royal Astronomical Society: Letters
Issue number1
StatePublished - Jun 2012


  • Accretion
  • Accretion discs
  • Black hole physics
  • Galaxies: jets
  • Gamma-ray burst: general
  • MHD
  • Methods: numerical

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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