Dynamic Process of Spontaneous Energy Radiation from Spinning Black Holes through Force-free Magnetic Field

• Published in: The Astrophysical journal Vol. 864; no. 2; pp. 173 - 184
• Main Authors: Koide, Shinji, Imamura, Tomoki
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 10.09.2018; IOP Publishing
• Subjects: Active galactic nuclei; Astrophysics; black hole physics; Black holes; Computational fluid dynamics; Computer simulation; Electromagnetic fields; Energy; Fluid flow; Force-free magnetic fields; Galaxy: nucleus; High energy astronomy; Magnetic fields; Magnetohydrodynamics; methods: analytical; numerical; Numerical simulations; plasmas; Radiation; Relativism; Relativistic effects; stars: black holes; Time dependence; Tsunamis
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/aad4fe

Recent general relativistic magnetohydrodynamic (MHD) simulations have suggested that relativistic jets from active galactic nuclei are powered by the rotational energy of central black holes through magnetic fields. Some mechanisms for the extraction of rotational energy of black holes have been proposed, such as the Penrose process, the Blandford-Znajek mechanism, the MHD/magnetic Penrose process, and superradiance. Among them, the Blandford-Znajek mechanism is the most promising as an important process of the central engines of the high-energy phenomena. However, a distinctive dynamic process of this mechanism has not yet been demonstrated intuitively, whereas extraction via the Penrose process has a simple interpretation. In this study, we performed numerical simulations of 1D force-free magnetodynamics (FFMD) with respect to the emergence of the Blandford-Znajek mechanism at the equatorial plane of the rapidly spinning black hole. A radial monopole-like magnetic field is used as an initial condition. We found a numerical solution of the steady-state region spreading from the ergosphere to the infinity point like a "tsunami." We can intuitively understand that this tsunami is caused and sustained by the degeneracy of the electromagnetic field of the perfect conducting plasma in the ergosphere. However, this degeneracy is not mathematically guaranteed in the time-dependent equations of FFMD. The degeneracy is given by an appropriate initial condition and is sustained by the condition at the "stretched horizon" of the black hole.