Our galaxy produces 9 trillion kilograms of antimatter a second—how?

Enlarge / That sharp red line is the high-energy radiation coming from our own galaxy, some of which is produced by the annihilation of antimatter. (credit: NASA/DOE/Fermi LAT Collaboration)

Antimatter is rare in this Universe, but the Universe is a pretty big place, so even small quantities can add up fast. In our galaxy alone, there's a steady bath of radiation that indicates positrons are constantly running into their electron anti-partners and annihilating them. Over something the size of a galaxy, that means there are lots of the positrons around. Estimates have it that 9.1 trillion kilograms of antimatter are being destroyed each second.

Where's it all coming from? We don't really know, but candidates have included everything from dark matter particles to supermassive black holes. A new paper suggests a relatively unexciting source: a specific class of supernova that produces lots of radioactive titanium, which decays by releasing a positron.

While positrons are produced by radioactivity here on Earth, they run into normal electrons almost instantly, a collision that annihilates both and releases an energetic photon. The interstellar material in space is so sparse, however, that it's thought that positrons typically travel for over 100,000 years before running into anything. That's long enough to blur out any individual sources and turn a single burst of positron production into a slow background of annihilations. So even if there are objects that produce positrons, we'd have a hard time spotting them.

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