  An anomalous gamma-ray excess emission has been found in Fermi Large Area
Telescope data covering the centre of the Galaxy. Several theories have been
proposed for this `Galactic Centre Excess'. They include self-annihilation of
dark matter particles, an unresolved population of millisecond pulsars, an
unresolved population of young pulsars, or a series of burst events. Here we
report on a new analysis that exploits hydrodynamical modelling to register the
position of interstellar gas associated with diffuse Galactic gamma-ray
emission. We find evidence that the Galactic Centre Excess gamma rays are
statistically better described by the stellar over-density in the Galactic
bulge and the nuclear stellar bulge, rather than a spherical excess. Given its
non-spherical nature, we argue that the Galactic Centre Excess is not a dark
matter phenomenon but rather associated with the stellar population of the
Galactic bulge and nuclear bulge.
