The Positron Puzzle

The Positron Puzzle is a half-century old conundrum about the origin of the Galactic gamma-ray emission line at photon energies of 511 keV, and the shape of its morphology, showing a bulge-to-disk luminosity ratio of similar to 1 - unlike any astrophysical source distribution. Positrons (e(+)s) that have been cooled to the eV scale capture electrons (e(-)s) and form the intermediate bound state of Positronium (Ps) which decays on a nano-second timescale into two or three photons. Assuming the emission to originate from the Galactic bulge, centre, and disk, a visible annihilation rate in the Milky Way of similar to 5 x 10(43) e(+) s(-1) has to be explained, either by a quasi-steady state of production and annihilation, or by possibly multiple burst-like events that flood the Galaxy with e(+)s, then fading away on a Myr timescale. In this paper, I will review what the real Positron Puzzle is, where data and simulations have been used inadequately which resulted in false claims and an apparent quandary, what we really know and absolutely not know about the topic, and how this epistemic problem might be advancing.

Automated summary

This paper reviews the true nature of the Positron Puzzle, the inadequate use of data and simulations leading to false claims and a clear dilemma, what we actually know and don't know about the topic, and how this epistemic problem might progress.