Conversion of protons to positrons by a black hole

TL;DR

This paper explores how black holes of certain masses can convert protons into positrons through pair production near their horizons, potentially explaining the observed 511 keV gamma-ray line.

Contribution

It introduces a mechanism for proton-to-positron conversion at black hole horizons involving electric field-induced pair production, a novel explanation for positron sources.

Findings

Black holes with masses 10^{18} to 10^{21} g can efficiently convert protons to positrons.

The process may produce positrons that contribute to the 511 keV gamma-ray line.

Electric fields near black hole horizons can reach critical levels for pair production.

Abstract

The conversion of protons to positrons at the horizon of a black hole (BH) is considered. It is shown that the process may efficiently proceed for BHs with masses in the range $\sim 10^{18}$ -- $10^{21}$ g. It is argued that the electric charge of BH acquired by the proton accretion to BH could create electric field near BH horizon close to the critical Schwinger one. It leads to efficient electron-positron pair production, when electrons are back captured by the BH while positrons are emitted into outer space. Annihilation of these positrons with electrons in the interstellar medium may at least partially explain the origin of the observed 511 keV line.