Acceleration of particles by Janis-Newman-Winicour singularities

TL;DR

This paper investigates how particles can achieve arbitrarily high energies during collisions near the naked singularities of Janis-Newman-Winicour spacetime, contrasting with black hole horizons where energies are limited.

Contribution

It demonstrates that high energy particle collisions are possible near JNW naked singularities, especially with a photon sphere, highlighting a potential observational distinction from black holes.

Findings

High energy collisions are generic near photon spheres in JNW spacetime.

Collision energy can be arbitrarily large near the naked singularity.

Energy growth varies with scalar field strength, being slow for small/large deviations and faster at intermediate levels.

Abstract

We examine here the acceleration of particles and high energy collisions in the the Janis-Newman- Winicour (JNW) spacetime, which is an extension of the Schwarzschild geometry when a massless scalar field is included. We show that while the center of mass energy of collisions of particles near the event horizon of a blackhole is not significantly larger than the rest mass of the interacting particles, in an analogous situation, it could be arbitrarily large in the JNWspacetime near the naked singularity. The high energy collisions are seen to be generic in the presence of a photon sphere in the JNW spacetime, whereas an extreme fine-tuning of the angular momentum of the colliding particles is required when the photon sphere is absent. The center of mass energy of collision near the singularity grows slowly for small and extremely large deviations from the Schwarzschild blackhole, but for intermediate strengths of the scalar field it rises moderately fast. As a possible and potentially interesting application, we point out that the presence of such high energy collissions may help the blackhole configurations to be distinguished from a naked singularity.