Supermassive black holes as possible sources of ultra high energy cosmic rays

Abstract

Production and acceleration mechanisms of ultra-high-energy cosmic rays (UHECRs) of energy $>10^{20}$eV, clearly beyond the GZK-cutoff limit remain unclear that points to exotic nature of the phenomena. Recent observations of extragalactic neutrino may indicate the source of UHECRs being an extragalactic supermassive black hole (SMBH). We demonstrate that ultra-efficient energy extraction from rotating SMBH driven by the magnetic Penrose process (MPP) could indeed foot the bill. We envision ionization of neutral particles, such as neutron beta-decay, skirting close to the black hole horizon that energizes protons to over $10^{20}$eV for SMBH of mass $10^9{M}_{\odot }$ and magnetic field of strength $10^4$G. Applied to Galactic center SMBH we have proton energy of order $\approx 10^{15.6}$eV that coincides with the knee of the cosmic ray spectra. We show that large ${\gamma }_z$ factors of high-energy particles along the escaping directions occur only in the presence of induced charge of the black hole that is known as the Wald charge in the case of uniform magnetic field. It is remarkable that the process neither requires extended acceleration zone, nor fine-tuning of accreting matter parameters. Further, this leads to certain verifiable constraints on SMBH's mass and magnetic field strength as UHECRs sources. This clearly makes ultra-efficient regime of MPP one of the most promising mechanisms for fueling UHECRs powerhouse.

14 pages, 6 figures

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• Dynamics of charged particles and magnetic dipoles around magnetized quasi-Schwarzschild black holes
• Lyapunov exponent ISCO and Kolmogorov Senai entropy for Kerr Kiselev black hole
• Geodesic Model of HF QPOs Tested for Black Holes in Spacetimes Reflecting the Effect of Surrounding Dark Matter
• Impact of electric charges on chaos in magnetized $Reissner-Nordstr\ddot{o}m$ spacetimes
• Dragged surfaces. On the accretion tori in the ergoregion
• Embedded BHs and multipole globules: Clustered misaligned thick accretion disks around static SMBHs
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• Blazar jets as possible sources of ultra-high energy photons: a short review
• Evolution of Braneworld Kerr-Newman Naked Singularities
• Charged fluids encircling compact objects: force representations and conformal geometries
• Electric Penrose process: high-energy acceleration of ionized particles by non-rotating weakly charged black hole