Extracting energy from plunging region of a Kerr-Taub-NUT black hole by magnetic reconnection

TL;DR

The paper tackles energy extraction from rotating black holes via magnetic reconnection in the plunging region of Kerr-Taub-NUT spacetimes, introducing a fast-reconnection framework that yields plasmoid energy-per-enthalpy $\epsilon_{\pm}$ and efficiency $\eta$. It shows that gravitomagnetic charge $l$ suppresses energy extraction while spin $a$ and magnetization $\sigma$ enhance it, with the feasible $\eta>1$ region shrinking as $l$ grows. By applying this mechanism to GRS 1915+105, the authors find an overlapping parameter region in $(l,a)$ where both jet power and radiative efficiency are explained, a result not achieved by prior models. The work provides a potential observational handle on gravitomagnetic effects and motivates further tests of Kerr-Taub-NUT gravity in strong-field regimes.

Abstract

We have studied the energy extraction from a Kerr-Taub-NUT black hole via magnetic reconnection occurring in the plunging region. Our results show that the gravitomagnetic charge suppresses the energy extraction process through magnetic reconnection and reduces the corresponding extraction efficiency, which is opposite to the effects of the black hole spin and the magnetization parameter. Finally, we treat the energy extraction process through magnetic reconnection as a mechanism to revisit the problem of the observed jet power and radiative efficiency of GRS 1915+105. Our results show that the allowed black hole parameter region originating from the jet power has an intersection with the region from the radiative efficiency. This means that with this mechanism related to magnetic reconnection the Kerr-Taub-NUT metric can simultaneously explain the observed jet power and radiative efficiency for GRS 1915+105, which is not explained by other mechanisms in previous studies.

Figures (9)

• Figure 1: Behaviors of the magnetic field angle in the bulk plasma plunging from the ISCO in Kerr-Taub-NUT geometry. Top: Change of the magnetic field angle with the radial coordinate $r$ for different black hole spin $a$ and gravitomagnetic charge $l$. Bottom: The value of $\xi$ at the event horizon $r_H=M+\sqrt{M^2-a^2+l^2}$ with different $a$ and $l$.
• Figure 2: The energy per unit enthalpy $\epsilon_-$ at infinity of the ejected plasmoids varies with the reconnection location, for different values of $a$, $l$ and $\sigma$ in $\tilde{p} = 1/4$.
• Figure 3: The radii of reconnection locations with the gravitomagnetic charge $l$ for different value of $\beta^\phi$.
• Figure 4: The energy extraction efficiency as a function of the reconnection location for different values of $\sigma$ (Left), for different values of $a$ (Middle) and for different values of $l$ (Right).
• Figure 5: The maximal value of $\eta$ as a function of $a$, $l$ and $\sigma$, respectively. Bottom right: the relationship curves between $a$ and $l$ when the maximal value $\eta_{max}=1$ for different magnetization.