511 keV Galactic Photons from a Dark Matter Spike

TL;DR

This paper suggests that a dark matter spike near the Galactic Center's black hole could explain the observed 511 keV gamma-ray line, aligning with existing constraints and offering testable predictions.

Contribution

It introduces a dark matter spike model around Sgr A* as a source of the 511 keV line, compatible with observational constraints and providing a new explanation for the emission.

Findings

Dark matter spike can account for the 511 keV line intensity.

Dark matter mass up to ~20 MeV is consistent with observations.

Future observations can test the proposed model.

Abstract

We propose that a dark matter (DM) spike around the Galactic Center's (GC) supermassive black hole, Sgr A*, could account for most of the bulge's measured 511 keV line intensity while remaining cosmologically compatible. DM annihilation can be the primary source of the 511 keV line emission without violating constraints from disk emission observations and in-flight positron annihilation with the interstellar medium, provided the disk emission is dominated by an astrophysical source of low-energy positrons. We find that a DM mass up to approximately 20 MeV, either with a Gondolo-Silk spike or one softened by stellar heating, could explain the observed 511 keV bulge emission profile. Our proposal can be tested by future observations of the continuum diffuse emission close to the GC.