Comment on "Black Holes are Neither Particle Accelerators Nor Dark Matter Probes"

TL;DR

This paper clarifies misconceptions about the Banados-Silk-West effect, demonstrating that the energy at infinity of particles colliding near a black hole horizon does not necessarily vanish due to redshift.

Contribution

It refutes previous claims that the energy at infinity vanishes near the black hole horizon, providing a corrected analysis of the effect.

Findings

Energy at infinity can remain finite near the horizon

Redshift does not always lead to zero energy at infinity

The effect's implications for black hole physics are clarified

Abstract

The Banados-Silk-West effect consists in the possibility to get infinite energy in the centre of mass frame of two particles colliding near the black hole horizon. According to S. T. McWilliams, Phys. Rev. Lett. 110 (2013) 011102, the energy at infinity of the outcome vanishes because of infinite redshift when the point of collision approaches the horizon. I show that this is not so.