Particles acceleration by Bocharova-Bronnikov-Melnikov-Bekenstein black hole

TL;DR

This paper investigates how scalar fields influence particle orbits, accretion efficiency, and collision energies around BBMB black holes, revealing significant effects on orbital dynamics and potential for ultra-high-energy cosmic ray acceleration.

Contribution

It provides analytical expressions and detailed analysis of particle motion, accretion efficiency, and collision energies in the context of BBMB black holes with scalar fields, highlighting novel effects of scalar coupling.

Findings

ISCO and marginally bound orbit radii are affected by scalar coupling.

Accretion efficiency varies with scalar coupling, reaching up to 30%.

Center-of-mass energy of colliding particles can become infinite near the horizon.

Abstract

We have studied the motion of massive particles under the influence of scalar and gravitational fields, with particular emphasis on the BBMB black hole. It has been shown that the radius of the innermost stable circular orbit (ISCO) and marginally bound orbit are significantly affected by the scalar coupling parameter. We study the energy efficiency of thin accretion disks around BBMB black holes, showing that the efficiency decreases for positive $g_s$ and increases for negative $g_s$, with a maximum of approximately $30\%$ for specific $g_s$ values. We derive analytical expressions for the angular and linear velocities of orbiting particles, highlighting their dependence on $g_s$. The photon sphere is shown to be independent of $g_s$, but the linear velocity at the ISCO position varies significantly, with massive particles behaving like ultra-relativistic particles near the black hole under scalar field influence. Additionally, we examine the center-of-mass energy (CME) of colliding particles near the BBMB black hole, showing that the scalar field can lead to infinitely high CME near the horizon, consistent with the BSW process. Astrophysical implications include CME values reaching \(10^{20} \, {\rm eV}\), comparable to the energies of ultra-high-energy cosmic rays (UHECR).