Primordial black holes and the observed Galactic 511 keV line

TL;DR

This paper explores whether primordial black holes with specific masses could explain the Galactic 511 keV line by emitting positrons, photons, and neutrinos, potentially accounting for dark matter.

Contribution

It proposes a novel hypothesis that slowly evaporating primordial black holes could produce positrons and gamma rays, offering a new explanation for the Galactic 511 keV line.

Findings

Primordial black holes of mass around 10^{16}-10^{17} g can emit positrons.

Photon flux from these black holes may be observable soon.

Neutrino flux from these black holes is below current detection thresholds.

Abstract

The observed 511 keV line from the Galactic Bulge is a real challenge for theoretical astrophysics: despite a lot of suggested mechanisms, there is still no convincing explanation and the origin of the annihilated positrons remains unknown. Here we discuss the possibility that a population of slowly evaporating primordial black holes with the mass around $10^{16}-10^{17}$ g ejects (among other particles) low--energy positrons into the Galaxy. In addition to positrons, we have also calculated the spectrum and number density of photons and neutrinos produced by such black holes and found that the photons are potentially observable in the near future, while the neutrino flux is too weak and below the terrestrial and extra--terrestrial backgrounds. Depending on their mass distribution, such black holes could make a small fraction or the whole cosmological dark matter.