For 20 years gamma‐ray astronomers have been reporting intermittent evidence of positron‐annihilation gammas coming from the vicinity of the center of our Galaxy. Much speculation about what's going on in the hidden heart of the Milky Way has been fueled by these sporadic sightings of 511‐keV gammas. (When an electron–positron pair at rest annihilates into two photons, the result is a pair of back‐to‐back 511‐keV gammas.) The most spectacular notion attributed the positrons to the workings of a monstrous black hole of some 106 solar masses, residing at the dynamical center of the Galaxy.

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