Cosmic reionization by primordial cosmic rays

TL;DR

This paper proposes that primordial cosmic rays from early microquasars could have significantly contributed to cosmic reionization, a process not fully explained by known sources, by quantifying their ionization power through particle cascade simulations.

Contribution

It introduces a novel hypothesis that cosmic rays from early microquasars played a key role in reionization, supported by detailed simulation analysis.

Findings

Cosmic rays could have contributed as much as X-rays to reionization.

The ionization impact depends on the electron-to-proton ratio in microquasar jets.

Primordial magnetic fields of around 10^{-17} G enhance cosmic ray ionization effects.

Abstract

After the so-called cosmic recombination, the expanding universe entered into a period of darkness since most of the matter was in a neutral state. About a billion years later, however, the intergalactic space was once again ionized. The process, known as the cosmic reionization, required the operation of mechanisms that are not well understood. Among other ionizing sources, Population III stars, mini-quasars, and X-ray emitting microquasars have been invoked. In this article we propose that primordial cosmic rays, accelerated at the termination points of the jets of the first microquasars, may have contributed to the reionization of the intergalactic space as well. For this we quantify the ionization power of cosmic rays (electrons and protons) in the primordial intergalactic medium using extensive particle cascade simulations. We establish that, depending on the fraction of electrons to protons accelerated in the microquasar jets, cosmic rays should have contributed to the reionization of the primordial intergalactic medium as much as X-rays from microquasar accretion disks. If the primordial magnetic field was of the order of $10^{-17}$ G, as some models suggest, cosmic rays had an important role in ionizing the neutral material far beyond the birth places of the first stars.