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 $2 \times 10^{9}\ \mathrm{eV}$ 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 $5 \times 10^{43}$ 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.