Hawking-Radiation Recoil of Microscopic Black Holes

TL;DR

This paper investigates the recoil effects during the final evaporation stage of microscopic black holes, suggesting they could acquire significant velocities that challenge their role as dark matter candidates.

Contribution

It introduces the concept that black hole evaporation recoil can impart high velocities, impacting dark matter models and primordial black hole formation theories.

Findings

Black hole remnants can reach velocities up to 0.1c due to recoil.

Recoil effects could conflict with cold dark matter cosmology.

Primordial black hole formation must have ceased early after inflation.

Abstract

Hawking radiation would make microscopic black holes evaporate rapidly, which excludes them from many astrophysical considerations. However, it has been argued that the quantum nature of space would alter this behaviour: the temperature of a Planck-size black hole vanishes, and what is left behind is a Planck-mass remnant with the cross-section of $\approx 10^{-70}\mbox{m}^2$, which makes a direct observation nearly impossible. Such black hole remnants have been identified as possible dark matter candidates. Here, we argue that the final stage of evaporation has a recoil effect that gives them a velocity up to $\approx 10^{-1} c$. This would lead to a disagreement with the cold dark matter cosmological model unless the primordial black hole formation ceased shortly after the inflation era.