Wikipedia: "Annihilation radiation is a term used in Gamma spectroscopy for the photon radiation produced when a particle and its antiparticle collide and annihilate. Most commonly, this refers to 511-keV photons produced by an electron interacting with a positron."
In our galaxy center, an extra than expected amount of gamma radiation is observed. However, now a study rules out dark matter destruction as the origin of extra radiation in the galaxy center. see: see: https://www.sciencedaily.com/releases/2020/08/200826151302.htm
However in Q-FFF Theory, it takes the 511 keV (Wikipedia) as base, with particle pair annihilation as origin. How pair production is created? by the new physics pair production at the local collider horizons of all the black holes crowding in the center of the Milky Way.
So the black hole horizon should be interpreted as the vacuum particle collider to produce these pairs, which produce the extra gamma rays from all over the bar shaped center of the milky way.