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In this paper we examine various issues closely related to the ongoing discussion on the nature of the Blandford-Znajek mechanism of extraction of rotational energy of black holes. In particular, we show that switch-on and switch-off shocks…
The Grad--Shafranov approach to the problem of the structure of the black hole magnetosphere is discussed. For the double transonic flow, the number of boundary conditions in the pair creation region is shown to be sufficient to determine…
We investigate the possibility that gamma-ray bursts are powered by a central engine consisting of a black hole with an external magnetic field anchored in a surrounding disk or torus. The energy source is then the rotation of the black…
We discuss one of the possible origins of large-scale magnetic fields based on a continuous distribution of toroidal electric current flowing in the inner region of the disc around a Kerr black hole (BH) in the framework of general…
A rotating black hole probably powers ultrarelativistic jets in gamma-ray bursts, relativistic jets from some active galactic nuclei, and jets from some black hole x-ray binaries. Prior estimates of the power output of a black hole have…
We study force-free magnetospheres in the Blandford-Znajek process from rapidly rotating black holes by adopting the near-horizon geometry of near-extreme Kerr black holes (near-NHEK). It is shown that the Znajek regularity condition on the…
The interaction of large scale magnetic fields with the event horizon of rotating black holes (the Blandford-Znajek [1977] mechanism) forms the basis for some models of the most relativistic jets. We explore a scenario in which the central…
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…
Black holes can accumulate a large amount of energy, responsible for highly energetic astrophysical phenomena Recently, fast magnetic reconnection (MR) of the magnetic field was proposed as a new way to extract energy and in this paper, we…
Relativistic jets from black holes can extract energy not only from accretion but also directly from the black hole's spin, as described by the Blandford-Znajek mechanism. A longstanding question is whether magnetic flux can accumulate near…
In this lecture I give an introduction to the rotational energy extraction of black holes by the electromagnetic Blandford-Znajek process and the generation of relativistic jets. After some basic material on the electrodynamics of black…
It is widely believed that some classes of high-energy transients may be powered by the rotational energy of a rapidly spinning black hole. The energy extraction mechanism commonly discussed involves macroscopic magnetic fields that are…
The expulsion of axisymmetric magnetic field from the event horizons of rapidly rotating black holes has been seen as an astrophysically important effect that may significantly reduce or even nullify the efficiency of the Blandford-Znajek…
Recent work has called into question whether nature can extract the rotational energy of a black hole via electromagnetic fields by appealing to an alleged ability to absorb current. We describe the strategies needed to properly treat the…
We analyze the constraint equation giving allowed solutions describing fields and currents in a force-free magnetosphere around a rotating black hole. Utilizing the divergence properties of the energy and angular-momentum fluxes for…
Some active galactic nuclei, microquasars, and gamma ray bursts may be powered by the electromagnetic braking of a rapidly rotating black hole. We investigate this possibility via axisymmetric numerical simulations of a black hole…
The Blandford-Znajek process, the steady electromagnetic energy extraction from a rotating black hole, is widely believed to work for driving relativistic jets, although it is still under debate where the electric current is driven. We…
Despite their potential importance for understanding astrophysical jets, physically realistic exact solutions for magnetospheres around Kerr black holes have not been found, even in the force-free approximation. Instead approximate…
It was suggested that the relativistic jets in gamma-ray bursts (GRBs) are powered via the Blandford-Znajek (BZ) mechanism or the annihilation of neutrinos and anti-neutrinos from a neutrino cooling-dominated accretion flow (NDAF). The…
The Fundamental Plane (FP) of Black Hole (BH) Activity in galactic nuclei relates X-ray and radio luminosities to BH mass and accretion rate. However, there is a large scatter exhibited by the data, which motivated us for a new variable. We…