Sombrero Galaxy as an Accelerator of Ultrahigh Energy Cosmic Ray Nuclei
Luis A. Anchordoqui, Karem Peñaló Castillo
TL;DR
This paper proposes that the Sombrero Galaxy can accelerate ultrahigh-energy cosmic ray (UHECR) nuclei near its central spinning supermassive black hole through the Blandford-Znajek mechanism, with the accelerator’s luminosity anti-correlated with the host’s infrared photon density. By balancing acceleration timescales against curvature-radiation losses and nucleus-photon interactions in a low-photon-density environment, heavy nuclei (e.g., $^{28}$Si, $^{56}$Fe) can reach energies above the observed maximum on Earth, while lighter nuclei are limited. The authors show that the UHECR luminosity scales roughly as $M_ullet^2$ since the Bondi accretion rate grows as $M_ullet^2$ and the near-horizon photon density is suppressed by the same factor, making Sombrero a viable, low-emission, high-energy accelerator. They discuss associated $\gamma$-ray signatures from curvature radiation and possible $\gamma\gamma$ absorption, and argue that the neutrino output would be strongly suppressed, consistent with current IceCube data, while offering observational tests with future UHECR and neutrino observations to validate the hidden-source paradigm.
Abstract
Motivated by a recent proposal that points to the Sombrero galaxy as a source of the highest energy cosmic rays, we investigate the feasibility of accelerating light and heavy nuclei in the supermassive black hole located at the center of this dormant galaxy. We show that cosmic ray nuclei concentrated in the immediate vicinity of the supermassive black hole could be efficiently accelerated up to the maximum observed energies without suffering catastrophic spallations. Armed with our findings we stand against the conventional wisdom and conjecture that accelerators of the highest energy cosmic rays must anti-correlate with the (electromagnetic) source power.