A team of international astrophysicists led by ANU 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.
Story Source:
Materials provided by Australian National University.
Image : Artist's concept of the Milky Way Galaxy. GLAST will
provide detailed information on where stars are forming.
Credit: NASA JPL
Cecile G. Tamura
