  The 511 keV gamma emission from the galactic core may originate from a high
concentration ($\sim 10^{22}$) of primordial black holes (PBHs) in the core
each of whose Hawking radiation includes $\sim 10^{21}$ positrons per second.
The PBHs we consider are taken as near the lightest with longevity greater than
the age of the universe (mass $\sim 10^{12}$ kg; Schwarzschild radius $\sim 1$
fm). These PBHs contribute only a small fraction of cold dark matter,
$\Omega_{PBH} \sim 10^{-8}$. This speculative hypothesis, if confirmed implies
the simultaneous discovery of Hawking radiation and an early universe phase
transition.
