Does the Galactic center GeV excess come from dark matter or pulsars?
In plain words
Fermi satellite data show extra gamma rays near $2e9\ \mathrm{eV}$ from the inner galaxy, which could come from annihilating dark-matter particles or from a large hidden population of millisecond pulsars (old, fast-spinning neutron stars).
Precise statement
The Fermi-LAT excess (spectrum peaking near $1\text{ to }3\,\mathrm{GeV}$, extending $\sim 10\text{ to }20\,\mathrm{deg}$ from the Galactic center, luminosity of order $1e37\,\mathrm{erg/s}$) fits either dark-matter annihilation (mass $\sim 30\text{ to }70\,\mathrm{GeV}$ into b quarks, $\langle \sigma v\rangle \sim 2e-26\,\mathrm{cm}^3/\mathrm{s}$) or tens of thousands of unresolved bulge millisecond pulsars. Determine which. Answer: an identification at $5\sigma$ from morphology, photon-count statistics, radio pulsar counts, or matching signals in dwarf galaxies.
What would settle it
A radio census of bulge millisecond pulsars, or a dwarf-galaxy gamma-ray detection with the predicted annihilation cross-section.
Status in the literature
Unverified note
Through 2025, analyses disagree on whether the excess traces the stellar bulge or a spherical profile, and searches for bulge millisecond pulsars remain inconclusive.
Related problems
- More general than Radio detection of the predicted bulge millisecond pulsar population
- More general than Does the GeV excess follow the stellar bulge or a spherical halo?