Galactic center GeV excess and 511 keV line

5 problems

• Radio detection of the predicted bulge millisecond pulsar population

  Open

  If pulsars make the excess, deep radio surveys toward the bulge should find many of them.

• Does the GeV excess follow the stellar bulge or a spherical halo?

  Contested

  Pulsars would follow the elongated, box-shaped bulge of stars, while dark matter would make a round glow.

• Does the Galactic center GeV excess come from dark matter or pulsars?

  Contested

  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).

• What produces the Galaxy's 511 keV positron annihilation line?

  Open

  About 5e43 positrons per second annihilate in the Milky Way, mostly in the central bulge, and no known source class explains both the rate and the bulge-heavy pattern.

• How far do Galactic positrons travel before annihilating?

  Contested

  If positrons made in the disk can drift into the bulge before annihilating, ordinary disk sources could explain the bulge glow.