Radiative cooling effects on plasmoid formation in black hole accretion flows with multiple magnetic loops

¹ Tsung-Dao Lee Institute, Shanghai Jiao Tong University 1 Lisuo Road Shanghai 201210, PR China
² School of Physics and Astronomy, Shanghai Jiao Tong University 800 Dongchuan Road Shanghai 200240, PR China
³ Key Laboratory for Particle Physics, Astrophysics and Cosmology (MOE), Shanghai Key Laboratory for Particle Physics and Cosmology, Shanghai Jiao Tong University 800 Dongchuan Road Shanghai 200240, PR China
⁴ Institut für Theoretische Physik, Goethe-Universität Frankfurt Max-von-Laue-Str 1 D-60438 Frankfurt am Main, Germany
⁵ Research Center for Astronomy, Academy of Athens Soranou Efessiou 4 GR-11527 Athens, Greece
⁶ Institut für Theoretische Physik und Astrophysik, Universität Würzburg Emil-Fischer-Str. 31 D-97074 Würzburg, Germany
⁷ Max-Planck-Institut für Radioastronomie Auf dem Hügel 69 D-53121 Bonn, Germany

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Received: 3 November 2025
Accepted: 16 January 2026

Abstract

Context. We investigated the physics of black hole accretion flows, particularly focusing on phenomena like magnetic reconnection and plasmoid formation, which are believed to be responsible for energetic events such as flares observed from astrophysical black holes.

Aims. We aim to understand the influence of radiative cooling on plasmoid formation within black hole accretion flows that are threaded by multi-loop magnetic field configurations.

Methods. We conducted 2D and 3D two-temperature general relativistic magnetohydrodynamic simulations. By varying the magnetic loop sizes and the mass accretion rate, we explored how radiative cooling alters the accretion dynamics, disk structure, and properties of reconnection-driven plasmoid chains.

Results. Our results demonstrate that radiative cooling suppresses the transition to the magnetically arrested disk state by reducing magnetic flux accumulation near the horizon. It significantly modifies the disk morphology by lowering the electron temperature and compressing the disk, which leads to increased density at the equatorial plane and decreased magnetization. Within the current sheets, radiative cooling triggers layer compression and the collapse of plasmoids, shortening their lifetime and reducing their size, while the frequency of plasmoid events increases. Moreover, we observe enhanced negative energy-at-infinity density in plasmoids near the ergosphere, with its peaks corresponding to plasmoid formation events.

Conclusions. Radiative cooling plays a critical role in shaping both macroscopic accretion flow properties and microscopic reconnection phenomena near black holes. This suggests that radiative cooling modulates black hole energy extraction through reconnection-driven Penrose processes, highlighting its importance in models of astrophysical black holes.