Energy extraction from the accelerating Kerr black hole via magnetic reconnection in the plunging region and circular orbit region

TL;DR

This study addresses energy extraction from an accelerating Kerr black hole via magnetic reconnection in both the plunging region and circular orbit region. It adapts the Comisso–Asenjo process within a 3+1 formalism on the equatorial plane and defines the outflow energies $\epsilon_{\pm}$ and the efficiency $\eta$ as functions of the spin $a$, acceleration $A$, and reconnection location $r$. Key findings show that in the plunging region, acceleration enhances extraction near extremality and at larger reconnection radii, while away from extremality it hinders extraction; in circular orbits, acceleration reduces the permissible extraction region but increases efficiency regardless of extremality. Overall, the plunging region yields higher energy-extraction efficiency than circular orbits, indicating that external acceleration can modulate magnetically mediated energy extraction around rotating black holes with potential astrophysical implications.

Abstract

Based on the magnetic reconnection mechanism, this study investigates how to extract energy effectively from an accelerating Kerr black hole in the plunging region and circular orbit region. After introducing the properties of accelerating black holes, including the event horizon, ergosphere, circular orbits, and innermost stable circular orbit, we investigate the magnetic reconnection process in the plunging region. Specifically, we analyze variations of the azimuthal angle with respect to the acceleration, examine changes in energy per enthalpy of decelerated plasma, and plot energy extraction efficiency along with permissible energy extraction regions. Results show that in the plunging region, at larger radii of reconnection locations, the accelerating black hole exhibits higher energy extraction efficiency than a Kerr black hole. Away from extremality, the acceleration parameter impedes energy extraction, while near extremality, it enhances extraction. We also study energy extraction in circular orbit region by plotting energy extraction efficiency within permissible regions. We find that the permissible energy extraction area is reduced and the efficiency exceeds that of Kerr black holes due to the existence of acceleration parameter. Larger acceleration parameters yield more effective energy extraction regardless of extremality, which is different from that in the plunging region. Additionally, energy extraction efficiency in the plunging region surpasses that in the circular orbit region, aligning with prior conclusions.

Figures (9)

• Figure 1: (a) Variation of the azimuthal angle $\xi$ with $r$ for different values of $A$. (b) Logarithmic graph of the absolute value of $\xi$. (c) Logarithmic graph of the absolute value of $\xi$ when r is relatively low.
• Figure 2: Variation of the azimuthal angle $\xi$ with $A$ at the event horizon.
• Figure 3: Variation of $\epsilon_-$ with $r$ for different values of $A$.
• Figure 4: Variation of energy extraction efficiency with $r$.
• Figure 5: (a) Permissible energy extraction regions in the plunging region. (b) Partial magnification images of (a).