Hotspot Image Driven by Magnetic Reconnection in Kerr-anti-de Sitter Black Holes

TL;DR

The paper investigates hotspot images produced by magnetic reconnection-driven plasmoid ejections near Kerr-AdS black holes using the Comisso-Asenjo mechanism. It combines a corotating Keplerian current-sheet model, a Gaussian hotspot emissivity, and backward ray-tracing in a Kerr-AdS geometry to produce time-resolved images and light curves. The key finding is that three flares appear within the observing window, with the first flare tied to energy extraction from the decelerated plasmoid ($\varepsilon_{-}$) and the subsequent flares arising from the accelerated plasmoid ($\varepsilon_{+}$) Doppler blueshifts, and that the hotspot image enlarges as the absolute value of the cosmological constant $|\Lambda|$ increases. The results hold across multiple parameter sets and emphasize the significant impact of $\Lambda$ on horizon-scale observables, while remaining robust for $\Lambda=0$ Kerr comparison cases. This work broadens the context of black-hole imaging by linking AdS/cosmological-constant effects to observable hotspot signatures.

Abstract

Based on the Comisso-Asenjo mechanism, we investigate the kinematic images of plasma before and after magnetic reconnection in Kerr-Anti-de Sitter(Kerr-AdS) black holes. Following a brief review of the Comisso-Asenjo process in Kerr-AdS black holes, we introduce the hotspot model and the imaging method. Building upon these foundational theories, we obtain the trajectory of the plasma and the temporal evolution of the hotspot images. It is found that there are three flares within the observing time, which is driven by the Comisso-Asenjo mechanism. We also discuss the influence of the cosmological parameter on the hotspot imaging. The results indicate that the hotspot image enlarges as the absolute value of $Λ$ increases, demonstrating that the cosmological constant significantly affects the hotspot.

Figures (8)

• Figure 1: Time evolution of the plasma hotspot distribution for $\Lambda=-0.00002$.
• Figure 2: $\Lambda=-0.00002$. (a) Trajectory of the plasmoid in a two-dimensional Cartesian coordinate system. Cyan represents the state before magnetic reconnection, yellow represents the accelerated plasma, green represents the decelerated plasma, and black represents the black hole. (b) Normalized intensity distribution of the hotspot as seen by the observer, showing the time-averaged radiation intensity on the observation plane. The intensity values are normalized by $I/I_{MAX}$. The outer ring in the figure represents secondary or higher-order images. (c) Hotspot emission light curve, showing the total flux versus observed time. (d) The solid yellow line represents the light curve for $\varepsilon_{+}$ and the case before magnetic reconnection, the solid purple line represents the light curve produced solely by $\varepsilon_{-}$, and the black dashed line represents the total observed light curve. (e) Normalized hotspot intensity distribution produced solely by the $\varepsilon_{-}$ plasma.
• Figure 3: $\Lambda=-0.0002$. (a) Plasmoid trajectory in a 2D Cartesian coordinate system. (b) Normalized intensity distribution of the observed hotspot. (c) Emission light curve from the hotspot. (d) Light curves under the three different scenarios.
• Figure 4: $\Lambda=-0.0007$. (a) Plasmoid trajectory in a 2D Cartesian coordinate system. (b) Normalized intensity distribution of the observed hotspot. (c) Emission light curve from the hotspot. (d) Light curves under the three different scenarios.
• Figure 5: $\Lambda=-0.002$. (a) Plasmoid trajectory in a 2D Cartesian coordinate system. (b) Normalized intensity distribution of the observed hotspot. (c) Emission light curve from the hotspot. (d) Light curves under the three different scenarios.