A July 2026 Astronomy & Astrophysics paper reexamines a map of 511-kiloelectronvolt gamma rays built from 20.5 years of observations by the INTEGRAL space telescope. That energy is a signature of positrons, the antimatter counterparts of electrons, annihilating with electrons.
The familiar part of the map is bright emission from the Milky Way’s central bulge and fainter emission along its disk. The authors focused on several hotspots far from the Galactic plane. Those patches could be real signals, but the paper also warns that some may be artifacts of the image-reconstruction process.
The strongest clues follow clouds around the Milky Way
The two brightest high-latitude hotspots overlap Complex C and the Magellanic Stream, large clouds of gas around the Milky Way. Other patches fall in directions containing groups of nearby galaxies, including the regions around Andromeda, Ursa Major, Hydra and Virgo.
The alignment is suggestive, not a confirmed source identification. The underlying reconstruction estimated individual regions at roughly 2 to 4 sigma. The paper says the combined high-velocity-cloud regions are difficult to explain as background fluctuations, while exposure toward the nearby-galaxy regions is too limited to show strong evidence that those features are not background.
If the cloud-associated emission is real, positrons produced inside the Milky Way may be escaping before annihilating in gas outside its main disk. Under that interpretation, the researchers calculate that the galaxy’s total positron production rate could approach 10^44 per second, higher than estimates based only on annihilation inside the Galactic interstellar medium.
A future telescope could test the interpretation
The analysis also models how positron annihilation across many galaxies might contribute to the cosmic gamma-ray background. The contribution could remain at the percent level, though some assumptions about positron energy and star formation raise it above 10 percent at energies of several megaelectronvolts. That is a model result, not a measured share.
ESA says INTEGRAL’s mission ended in February 2025 after more than two decades, so confirming the faint features will require newer instruments. The Compton Spectrometer and Imager is designed to survey gamma rays from 0.2 to 5 megaelectronvolts and investigate the origins of Galactic positrons. Its team is preparing for a 2027 launch. If the findings are confirmed, the paper says next-generation MeV telescopes could identify individual extragalactic 511-keV sources.
