Somewhere beyond the familiar glow of the Milky Way, matter may be meeting its mirror image in a spectacular act of cosmic annihilation. A recent study suggests that our galaxy could be leaking antimatter into the vast darkness of intergalactic space, where these elusive particles collide with ordinary matter and disappear in flashes of energy.

A team of astronomers may have detected the gamma-ray signature produced when antimatter particles, or positrons, collide with electrons outside of the Milky Way for the first time. The findings, published in Astronomy & Astrophysics, could offer a rare glimpse of a hidden process unfolding at the edges of our galactic home.

Antimatter is, in a sense, the mirror image of ordinary matter. Every fundamental particle has an antimatter counterpart with the same mass but opposite electric charge or other reversed properties.

When antimatter encounters its matter counterpart, the two particles can annihilate, converting their mass into energy, typically in the form of gamma-ray photons—highly energetic light with a characteristic energy of 511 kiloelectronvolts (keV). Scientists can use these gamma rays as clues to antimatter’s whereabouts.

Using data from the European Space Agency’s (ESA) INTEGRAL telescope, the researchers behind the new study put together a detailed map of the Milky Way’s 511 keV emission.

The majority of the signals came from the central regions of the galaxy. This presented a problem: there appears to be far more positrons annihilating than expected. The known sources behind these signals, including black holes, neutron stars, and other highly energetic objects, could not account for how many positrons the Milky Way appears to produce.

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