DISRUPTED GLOBULAR CLUSTERS CAN EXPLAIN the GALACTIC CENTER GAMMA-RAY EXCESS

Abstract

The Fermi satellite has recently detected gamma-ray emission from the central regions of our Galaxy. This may be evidence for dark matter particles, a major component of the standard cosmological model, annihilating to produce high-energy photons. We show that the observed signal may instead be generated by millisecond pulsars that formed in dense star clusters in the Galactic halo. Most of these clusters were ultimately disrupted by evaporation and gravitational tides, contributing to a spherical bulge of stars and stellar remnants. The gamma-ray amplitude, angular distribution, and spectral signatures of this source may be predicted without free parameters, and are in remarkable agreement with the observations. These gamma-rays are from fossil remains of dispersed clusters, telling the history of the Galactic bulge.