The inner regions of our home galaxy, the Milky Way, have been known to strongly emit gamma-rays since over 40 years ago, which in turn suggested the presence of a large amount of antimatter in those regions. However, it is only now that we may be close to knowing where all that antimatter came from, and the answer could be supernovae.

Antimatter is a material composed of antiparticles of regular matter (such as a position for an electron and an antiproton for a proton, which can together form a molecule of antihydrogen), and when the two opposites come into contact, they completely destroy each other, a high-energy burst of gamma rays being the only remnant. This is what led scientists to consider the existence of antimatter in the regions near galaxy’s center.

A new study, led by astrophysicists from the Australian National University (ANU), published online Monday in the journal Nature Astronomy, says the source of all that antimatter is not the annihilation of dark matter or the supermassive black hole sitting at the center of the galaxy, but instead “a series of weak supernova explosions over millions of years, each created by the convergence of two white dwarfs which are ultra-compact remnants of stars no larger than two suns.”

Read: New CERN Experiment To Find Matter-Antimatter Asymmetry

White dwarfs are essentially the compact cores of stars that have run out of fuel and shed their outer layers. Even the sun, after it is done ballooning into a red giant, will eventually collapse into a white dwarf.

Explaining the phenomenon, Roland Crocker from ANU said in a statement that the antimatter was created when two white dwarfs first formed a binary system and then collided with each other. As a result of the collision, the smaller of the two stars would lose mass to the larger star. The former ends its existence as a helium white dwarf and the latter ends life as a carbon-oxygen white dwarf. The larger star then rips apart its smaller companion and gets covered in a dense shell of helium. That leads quickly to a thermonuclear supernova explosion, which is the source of antimatter.

“The binary system is granted one final moment of extreme drama: as the white dwarfs orbit each other, the system loses energy to gravitational waves causing them to spiral closer and closer to each other,” Crocker said in the statement. “Our research provides new insight into a part of the Milky Way where we find some of the oldest stars in our galaxy,” he added.

The stars he refers to, which are also the precursors of the supernovae mentioned in the study, are about three to six billion years old.

The study, titled “Diffuse Galactic antimatter from faint thermonuclear supernovae in old stellar populations,” had contributions from a dozen other researchers from various countries.

Antimatter has been a subject of great interest, especially for its potential practical applications, such as for powering spaceships that can travel much faster than anything at present. While the concept, like many others, first appeared in science fiction (and cartoons like Futurama), it has since been advanced theoretically. CERN also conducts regular research into antimatter, exploring various facets of this still poorly understood substance.