Enhanced energy extraction via magnetic reconnection in Kerr-AdS spacetime

TL;DR

This paper addresses whether energy can be extracted from Kerr-AdS black holes via magnetic reconnection and how a negative cosmological constant affects the mechanism. By calculating the energy-at-infinity per enthalpy in the ZAMO frame, deriving extraction conditions, and mapping parameter spaces, the authors show that Λ<0 broadens the viable reconnection regions and enhances efficiency and power, particularly near the circular corotating photon orbit. The results indicate Kerr-AdS generally outperforms Kerr in small-radius reconnection scenarios and enable energy extraction at lower spins than in asymptotically flat spacetimes. Overall, the cosmological constant emerges as a crucial factor shaping magnetic-reconnection energy extraction from rotating black holes.

Abstract

In this paper, we study the energy extraction from Kerr-AdS black holes following the magnetic reconnection process. The parameter space regions that satisfy the energy extraction condition, as well as the efficiency and power of the extracted energy, are analyzed. The study shows that the presence of a negative cosmological constant extends the range of dominant reconnection radial locations where the energy extraction condition is met, and enables energy extraction even from black holes with relatively low spin. Furthermore, the influence of the negative cosmological constant on energy extraction is modulated by the extent of the dominant reconnection radial region: a more negative cosmological constant enhances the extracted energy, efficiency, and power, particularly for smaller dominant reconnection radii. These results demonstrate that the energy extraction from Kerr-AdS black holes is more favorable than that from their asymptotically flat counterparts. Our results highlight the crucial role of the cosmological constant in energy extraction via magnetic reconnection.

Figures (11)

• Figure 1: Parameter space allowed the existence of Kerr-AdS black holes in $a/M-\Lambda M^2$ plane (shaded region). The solid line denotes the extremal Kerr-AdS black holes.
• Figure 2: The characteristic radii for the black holes. The outer event horizon $r_+$, outer ergosphere boundary $r_E$, and the circular corotating photon orbit $r_{LR}$, are described by the red solid curves, black solid curves, and purple dashed curves, respectively. (a) $r/M$ vs. $\Lambda M^2$. (b) $r/M$ vs. $a/M$.
• Figure 3: The behaviors of $\epsilon^\infty_+$ (solid curves) and $\epsilon^\infty_-$ (dashed curves) as functions of spin $a/M$ for different values of the plasma magnetization of plasma $\sigma_0$, the orientation angle $\xi$, and the dominant reconnection radial location $r/M$, and with cosmological constant $\Lambda M^2=-0.01$ fixed. The plasma magnetization $\sigma_0$ = 5, 10, 15, and 20 from bottom to top for solid curves and from top to bottom for dashed curves.
• Figure 4: The behaviors of $\epsilon^\infty_+$ (solid curves) and $\epsilon^\infty_-$ (dashed curves) as functions of the cosmological constant $\Lambda M^2$ for different values of the plasma magnetization of plasma $\sigma_0$, the orientation angle $\xi$, and the dominant reconnection radial location $r/M$, and with spin $a/M=0.99$ fixed. The plasma magnetization $\sigma_0$ = 5, 10, 15, and 20 from bottom to top for solid curves and from top to bottom for dashed curves. (a) $r/M=1.15$, $\xi=\pi/12$. (b) $r/M=1.15$, $\xi=\pi/12$. (c) $r/M=1.35$, $\xi=\pi/12$. (d) $r/M=1.35$, $\xi=\pi/12$. (e) $r/M=1.75$, $\xi=\pi/12$. (f) $r/M=1.75$, $\xi=\pi/12$. (g) $r/M=1.15$, $\xi=\pi/6$. (h) $r/M=1.15$, $\xi=\pi/6$. (i) $r/M=1.35$, $\xi=\pi/12$. (i) shows the behavior of $\epsilon^\infty_{-}$ when $\sigma_0$ is set to 5 in (d).
• Figure 5: Regions of parameter space $\Lambda M^2-r/M$ satisfying the energy extraction condition $\epsilon^\infty_{-}<0$ with $a/M=0.99$. Red solid curves, black solid curves, and purple dashed curves represent the radii of the outer event horizon $r_+$, outer ergosphere boundary $r_E$, and the circular corotating photon orbit $r_{LR}$, respectively. (a) $\sigma_0=1$ with $\xi=\frac{\pi}{6}$, $\frac{\pi}{8}$, $\frac{\pi}{12}$, $\frac{\pi}{20}$. (b) $\xi=\frac{\pi}{12}$ with $\sigma_0$=1, 5, 10, 20, 100.