Disrupted Globular Clusters and the Gamma-Ray Excess in the Galactic
  Centre
  The Fermi Large Area Telescope has provided the most detailed view toward the
Galactic Centre (GC) in high-energy gamma rays. Besides the interstellar
emission and point-source contributions, the data suggest a residual diffuse
gamma-ray excess. The similarity of its spatial distribution with the expected
profile of dark matter has led to claims that this may be evidence for dark
matter particle annihilation. Here, we investigate an alternative explanation
that the signal originates from millisecond pulsars (MSPs) formed in dense
globular clusters and deposited at the GC as a consequence of cluster inspiral
and tidal disruption. We use a semi-analytical model to calculate the
formation, migration, and disruption of globular clusters in the Galaxy. Our
model reproduces the mass of the nuclear star cluster and the present-day
radial and mass distribution of globular clusters. For the first time, we
calculate the evolution of MSPs from disrupted globular clusters throughout the
age of the Galaxy and consistently include the effect of the MSP spin-down due
to magnetic-dipole breaking. The final gamma-ray amplitude and spatial
distribution are in good agreement with the Fermi observations and provide a
natural astrophysical explanation for the GC excess.
