Where do positrons come from? A new 511 keV map hints at surprises

A new map of 511 keV positron annihilation radiation from 20 years of INTEGRAL observations shows hotspots at high galactic latitudes that don't match known Galactic sources. These could trace extragalactic positrons from nearby dwarf galaxies and the Magellanic Stream, implying a positron production rate 10× higher than previously measured. Next-generation MeV telescopes could resolve individual extragalactic sources for the first time.