2020/01/31 by J. F. Mahlmann, Amir Levinson, A. Levinson +2 · 3 citations
Physics and Astronomy · #Accretion (finance) #Active galactic nucleus #Advection #Astrophysical Phenomena and Observations #Astrophysical jet #Astrophysics #Astrophysics and Cosmic Phenomena #Black hole (networking) #Flux (metallurgy) #Galaxy #Magnetic field #Magnetic flux #Physics #Poynting vector #Pulsars and Gravitational Waves Research #Quantum mechanics #Rotating black hole #Spin-flip #Supermassive black hole #astro-ph.HE
paper · pdf · doi:10.1093/mnras/staa943
25 pages, 17 figures of which 17 are in color. 1 animated figure. Accepted by MNRAS
openalex created_date 2020/01/23 · openalex publication_date 2020/04/02 · arxiv created 2020/07/13 · arxiv updated 2020/07/15 · openalex updated_date 2026/08/05
ABSTRACT Black hole – accretion disc systems are the central engines of relativistic jets from stellar to galactic scales. We numerically quantify the unsteady outgoing Poynting flux through the horizon of a rapidly spinning black hole endowed with a rotating accretion disc. The disc supports small-scale, concentric, flux tubes with zero net magnetic flux. Our general relativistic force-free electrodynamics simulations follow the accretion on to the black hole over several hundred dynamical time-scales in 3D. For the case of counter-rotating accretion discs, the average process efficiency reaches up to 〈ϵ〉 ≈ 0.43, compared to a stationary energy extraction by the Blandford/Znajek process. The process efficiency depends on the cross-sectional area of the loops, i.e. on the product l × h, where l is the radial loop thickness and h its vertical scale height. We identify a strong correlation between efficient electromagnetic energy extraction and the quasi-stationary setting of ideal conditions for the operation of the Blandford/Znajek process (e.g. optimal field line angular velocity and fulfillment of the so-called Znajek condition). Remarkably, the energy extraction operates intermittently (alternating episodes of high and low efficiency) without imposing any large-scale magnetic field embedding the central object. Scaling our results to supermassive black holes, we estimate that the typical variability time-scale of the system is of the order of days to months. Such time-scales may account for the longest variability scales of TeV emission observed, e.g. in M87.