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by Will Wright
23 May 2017
from
ANU Website
The Milky Way.
Image:
Roanish, Flickr.
Our research provides
new insight
into a part of the Milky Way
where we find some of
the oldest stars in our galaxy.
A team of international astrophysicists led by
ANU (Australian National
University) has shown how most of
the antimatter in the Milky Way
forms.
Antimatter is 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.
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.
ANU researcher Dr Roland Crocker said the team 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 larger than two suns.
"Our research
provides new insight into a part of the Milky Way where we find
some of the oldest stars in our galaxy," said Dr Crocker 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.
He said 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.
"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," Dr
Crocker said.
He said once they became
too close the carbon-oxygen white dwarf ripped apart the companion
star whose helium quickly formed a dense shell covering the bigger
star, quickly leading to a thermonuclear supernova that was
the source of the antimatter.
The research (Diffuse
Galactic Antimatter from Faint Thermonuclear Supernovae in Old
Stellar Populations) is published in Nature Astronomy.
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