Prograde and retrograde black holes: whose jet is more powerful?
Article first published online: 19 APR 2012
© 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS
Monthly Notices of the Royal Astronomical Society: Letters
Volume 423, Issue 1, pages L55–L59, June 2012
How to Cite
Tchekhovskoy, A. and McKinney, J. C. (2012), Prograde and retrograde black holes: whose jet is more powerful?. Monthly Notices of the Royal Astronomical Society: Letters, 423: L55–L59. doi: 10.1111/j.1745-3933.2012.01256.x
- Issue published online: 4 JUN 2012
- Article first published online: 19 APR 2012
- Accepted 2012 March 19. Received 2012 February 26; in original form 2012 January 22
- accretion, accretion discs;
- black hole physics;
- methods: numerical;
- gamma-ray burst: general;
- galaxies: jets
The outflow efficiency (η) from black hole (BH) accretion disc systems is known to depend upon both the BH spin (a) 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.