Disrupted Globular Clusters and the Gamma-Ray Excess in the Galactic Centre

TL;DR

This paper proposes that the gamma-ray excess observed in the Galactic Centre can be explained by millisecond pulsars originating from disrupted globular clusters, offering an astrophysical alternative to dark matter hypotheses.

Contribution

It introduces a semi-analytical model for globular cluster evolution and MSP formation, successfully matching observed gamma-ray data without invoking dark matter.

Findings

Model reproduces the mass and distribution of globular clusters.

MSP evolution from disrupted clusters matches gamma-ray excess.

Provides an astrophysical explanation for the gamma-ray excess.

Abstract

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.