We provide a semi-analytic comparison between the Blandford-Znajek (BZ) and the magnetic reconnection power for accreting black holes in the curved spacetime of a rotating black hole. Our main result is that for a realistic range of astrophysical parameters, the reconnection power may compete with the BZ power. The field lines anchored close to or on the black hole usually evolve to open field lines in general relativistic magnetohydrodynamic (GRMHD) simulations. The BZ power is dependent on the black hole spin while magnetic reconnection power is independent of it for the force-free magnetic configuration with open field lines adopted in our theoretical study. This has obvious consequences for the time evolution of such systems particularly in the context of black hole X-ray binary state transitions. Our results provide analytical justification of the results obtained in GRMHD simulations.
Jet Luminosity of Gamma-ray Bursts: Blandford-Znajek Mechanism v.s. Neutrino Annihilation Process
围绕旋转恒星质量黑洞的中微子吸积流是伽马射线暴的中心引擎之一。两种机制，即，BZ机制和中微子湮灭过程被认为是伽玛暴的动力学机制。利用Xue et al.（2013）的解析解，忽略磁场组态的影响，我们估算了BZ和中微子湮灭光度作为盘质量和BH自旋参数的函数，以对比观测到的伽玛暴喷流光度。结果表明，虽然中微子湮灭过程可以解释绝大多数的伽玛暴，但BZ机制更有效，特别是对于长持续时间的伽玛暴。实际上，如果把伽玛暴的余辉和耀斑的能量也包括在内，这两种机制的区别就更明显了。此外，大质量盘和高BH自旋有利于伽玛暴的高亮度。最后，我们讨论了可能的物理机制，以提高磁盘质量或中微子发射率的NDAF和这两种机制之间的相关差异。
Recently, it was claimed that accretion of electric charge by a black hole rotating in an aligned external magnetic field results in a "dead" vacuum magnetosphere, where the electric field is totally screened, no vacuum breakdown is possible, and the Blandford-Znajek mechanism cannot operate King & Pringle (2021). Here we study in details the properties of the Wald(1974) solution for electrically charged black holes discussed in that paper. Our results show that the claim is erroneous as in the solution with the critical charge $q_0=2aB_0$ there exists a drop of electrostatic potential along a…
We consider the Blandford-Znajek process of electromagnetic extraction of energy from a general axially symmetric asymptotically flat slowly rotating black hole. Using the general parametrization of the black-hole spacetime we construct formulas for the flux of the magnetic field and the rate of energy extraction, which are valid not only for the Kerr spacetime, but also for its arbitrary axially symmetric deformations. We show that in the dominant order these quantities depend only on a single deformation parameter, which relates the spin frequency of a black hole with its rotation parameter.
Comparison of gravitational waves from central engines of gamma-ray bursts: neutrino-dominated accretion flows, Blandford-Znajek mechanisms, and millisecond magnetars
We study the metric backreaction of mass and angular momentum accretion on black holes. We first develop the formalism of monopole and dipole linear gravitational perturbations around the Schwarzschild black holes in the Eddington-Finkelstein coordinates against the generic time-dependent matters. We derive the relation between the time dependence of the mass and angular momentum of the black hole and the energy-momentum tensors of accreting matters. As a concrete example, we apply our formalism to the Blandford-Znajek process around the slowly rotating black holes. We find that the time depen…
We examine the temporary evolution of axisymmetric magnetospheres around rapidly rotating black holes (BHs), by applying our two-dimensional particle-in-cell simulation code. Assuming a stellar-mass BH, we find that the created pairs fail to screen the electric field along the magnetic field, provided that the mass accretion rate is much small compared to the Eddington limit. Magnetic islands are created by reconnection near the equator and migrate toward the event horizon, expelling magnetic flux tubes from the BH vicinity during a large fraction of time. When the magnetic islands stick to th…
Jets launched by active galactic nuclei (AGN) are believed to play a significant role in shaping the properties of galaxies and provide an energetically viable mechanism through which galaxies can become quenched. Here we present a novel AGN feedback model, which we have incorporated into the AREPO code, that evolves the black hole mass and spin as the accretion flow proceeds through a thin $α$-disc which we self-consistently couple to a Blandford-Znajek jet. We apply our model to the central region of a typical radio-loud Seyfert galaxy embedded in a hot circumgalactic medium (CGM). We find t…
Relativistic polytrope from the collimation and acceleration profiles of the M87 jet at subparsec scales and thermodynamic evidence for the Blandford-Znajek mechanism
The Blandford and Znajek (BZ) split-monopole serves as an important theoretical example of the mechanism that can drive the electromagnetic extraction of energy from Kerr black holes. It is constructed as a perturbative low spin solution of Force Free Electrodynamics (FFE). Recently, Armas $et~al.$ put this construction on a firmer footing by clearing up issues with apparent divergent asymptotics. This was accomplished by resolving the behavior around the outer light surface, a critical surface of the FFE equations. Building on this, we revisit the BZ perturbative expansion, and extend the per…
University of Amsterdam（阿姆斯特丹大学）；Dutch Institute for Emergent Phenomena (DIEP)（荷兰涌现现象研究所）；Institute for Advanced Study, University of Amsterdam（阿姆斯特丹大学高等研究院）；Anton Pannekoek Institute（安东·潘内科克研究所）
We explore superradiance for Alfvén waves (Alfvénic superradiance) in an axisymmetric rotating magnetosphere of a Kerr black hole within the force-free approximation. On the equatorial plane of the Kerr spacetime, the Alfvén wave equation is reduced to a one-dimensional Schrödinger-type equation by separating variables of the wave function and introducing a tortoise coordinate mapping the inner and outer light surfaces to $-\infty$ and $+\infty$, respectively, and we investigate a wave scattering problem for Alfvén waves. An analysis of the asymptotic solutions of the wave equation and the con…
