TY - JOUR
T1 - Prograde and retrograde black holes
T2 - Whose jet is more powerful?
AU - Tchekhovskoy, Alexander
AU - McKinney, Jonathan C.
N1 - Copyright:
Copyright 2012 Elsevier B.V., All rights reserved.
PY - 2012/6
Y1 - 2012/6
N2 - 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.
AB - 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.
KW - Accretion
KW - Accretion discs
KW - Black hole physics
KW - Galaxies: jets
KW - Gamma-ray burst: general
KW - MHD
KW - Methods: numerical
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U2 - 10.1111/j.1745-3933.2012.01256.x
DO - 10.1111/j.1745-3933.2012.01256.x
M3 - Article
AN - SCOPUS:84863542188
VL - 423
SP - L55-L59
JO - Monthly Notices of the Royal Astronomical Society: Letters
JF - Monthly Notices of the Royal Astronomical Society: Letters
SN - 1745-3933
IS - 1
ER -