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Analytic dependence of particle acceleration efficiency on magnetohydrodynamic instability's growth parameters in Kerr black hole accretion disks.

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Title: Analytic dependence of particle acceleration efficiency on magnetohydrodynamic instability's growth parameters in Kerr black hole accretion disks.
Authors: Ha, Ji-Hoon1 (AUTHOR) hjhspace223@gmail.com
Source: Astrophysics & Space Science. Feb2026, Vol. 371 Issue 2, p1-10. 10p.
Subjects: Particle acceleration, Magnetohydrodynamic instabilities, Plasma pressure, Energy transfer, Accretion disks, Kerr black holes
Abstract: Magnetohydrodynamic (MHD) instabilities in accretion disks play a crucial role in mediating energy transfer, and their physical properties have therefore been extensively investigated. In this study, we analytically examine particle acceleration driven by such instabilities in the accretion disk around a Kerr black hole, focusing on the regime where particles experience strong frame-dragging effects. Using the linear growth rate of the magnetorotational instability (MRI) obtained from general relativistic MHD analysis, we explore the dependence of the turbulent acceleration timescale on the MRI growth rate and the turbulent Alfvén Mach number. Because the MRI growth rate depends on the black hole spin, the pressure anisotropy with respect to the magnetic field, and the plasma beta, the acceleration timescale becomes shorter as these parameters increase. By incorporating the energy loss timescale, we estimate the maximum Lorentz factor of the particles where the acceleration and loss timescales are balanced. Furthermore, we solve the steady-state Fokker-Planck equation including both energy diffusion and radiative loss terms to obtain the particle energy distribution. The resulting steady-state spectra and mean particle energy clearly demonstrate that the particle acceleration efficiency increases with the MRI growth rate throughout the accretion disk, over a broad range of spin and plasma beta values. Our results suggest that higher spin and pressure anisotropy enhance particle energies, which could be relevant for understanding high-energy astrophysical phenomena in active galactic nuclei. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract:Magnetohydrodynamic (MHD) instabilities in accretion disks play a crucial role in mediating energy transfer, and their physical properties have therefore been extensively investigated. In this study, we analytically examine particle acceleration driven by such instabilities in the accretion disk around a Kerr black hole, focusing on the regime where particles experience strong frame-dragging effects. Using the linear growth rate of the magnetorotational instability (MRI) obtained from general relativistic MHD analysis, we explore the dependence of the turbulent acceleration timescale on the MRI growth rate and the turbulent Alfvén Mach number. Because the MRI growth rate depends on the black hole spin, the pressure anisotropy with respect to the magnetic field, and the plasma beta, the acceleration timescale becomes shorter as these parameters increase. By incorporating the energy loss timescale, we estimate the maximum Lorentz factor of the particles where the acceleration and loss timescales are balanced. Furthermore, we solve the steady-state Fokker-Planck equation including both energy diffusion and radiative loss terms to obtain the particle energy distribution. The resulting steady-state spectra and mean particle energy clearly demonstrate that the particle acceleration efficiency increases with the MRI growth rate throughout the accretion disk, over a broad range of spin and plasma beta values. Our results suggest that higher spin and pressure anisotropy enhance particle energies, which could be relevant for understanding high-energy astrophysical phenomena in active galactic nuclei. [ABSTRACT FROM AUTHOR]
ISSN:0004640X
DOI:10.1007/s10509-026-04545-9