Scientists solve mystery of how most antimatter in the Milky Way forms

2 Jun 2017

A team of international astrophysicists led by ANU and including UQ astronomer Holger Baumgardt has shown how most of the antimatter in the Milky Way forms.

University of Queensland School of Mathematics and Physics Associate Professor Holger Baumgardt said that antimatter was material composed of the antiparticle partners of ordinary matter.

“When antimatter meets with matter, they quickly annihilate each other to form a burst of energy in the form of gamma-rays,” he said.

“Scientists have known since the early 1970s that the inner parts of the Milky Way galaxy are a strong source of gamma-rays, indicating the existence of antimatter, but there had been no settled view on where the antimatter came from.”

In a new study, published in May 2017, the team of astronomers had shown that the cause was 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 more massive than our sun.

"Our research provides new insight into a part of the Milky Way where we find some of the oldest stars in our galaxy," said Roland Dr Crocker, the lead author of the research project from the ANU Research School of Astronomy and Astrophysics.

Dr Crocker said the team had ruled out the supermassive black hole at the centre of the Milky Way and the still-mysterious dark matter as being the sources of the antimatter.

Instead the antimatter came from a system where two white dwarfs form a binary system and collide with each other.

The smaller of the binary stars loses mass to the larger star and ends its life as a helium white dwarf, while the larger star ends as a carbon-oxygen white dwarf.

As the white dwarfs orbit each other, the system loses energy to gravitational waves causing the white dwarfs to spiral closer and closer to each other until the carbon-oxygen white dwarf rips apart the companion star whose helium forms a dense shell covering the bigger star, quickly leading to a thermonuclear supernova that is the source of the antimatter.

The research is published in Nature Astronomy.