InsideScience:
Astronomers meeting in Washington last week announced that a
recent search for supernovae found something quite unusual:
antimatter.Usually
stars like our Sun are powered by fusion reactions in which the
nuclei of two atoms fuse together to form a heavier nucleus. In
Y-155, a star in the constellation Cetus, the astronomers argue
that another process was crucial: the making and unmaking of
antimatter particles.In all stars a titanic struggle takes
place between gravity, which wants to draw matter toward the
center of the star, and the pressure of nuclear interactions,
which tends to keep the star inflated as if it were a balloon.
Only when the star uses up all its internal fuel, causing the
nuclear reactions to slow down, does gravity start to win out.
The resulting gravitational collapse is what causes the star to
explode. When a star dies in this way, as a supernova, it often
spews matter into space and can be brighter than its host
galaxy, at least for a short time. Astronomers love to study
such supernovae since they say a lot about the inner mechanisms
of stars and also provide a yardstick for determining how far
away the star was.Notre Dame astronomer
Peter
Garnavich reports that what makes Y-155 different is its
mass, an estimated 200 times heavier than our Sun. With such a
large mass, the pressure at the core of the star is so great
that the light released in nuclear reactions is capable of
creating new particles, electron–antielectron pairs. The
creation of these particles actually hastens the collapse of
the star and its eventual explosion.The idea of a supernova
triggered by the creation of antimatter has been around for
only about 40 years, Garnavich said, but the observational
evidence is sparse. In the case of Y-155 the signature light
cast out after the explosion was odd: most ssupernovae send out
higher-energy blue light first followed by cooler red light,
but in this case the red light came first then the blue. That
and the much larger amount of radioactive nickel shooting
outwards compared to common supernovae led the researchers to
suspect that antimatter was involved in triggering the
explosion.Garnavich is part of a team of scientists
participating in a project called
ESSENCE.
Using a 4-meter-wide telescope mirror at high altitudes in
Chile, the scientists observed 200 of the most explosive type
of supernova. Y-155 was the most explosive of them all.The
Keck Telescope on
Hawaii was directed at Y-155 so that an accurate
spectrum—that is, a summary of all the light coming from
the star—could be recorded. This allowed the distance to
the star to be determined. At a distance of 7 billion
light-years, this star lies about halfway back in time toward
the origin of the universe.Garnavich said that because of its
size and powerful emission, Y-155 might resemble the first
generation of stars in the universe. Another ESSENCE scientist,
Alex
Filippenko of the University of California, Berkeley, said
that the antimatter-supernova mechanism might be important in
locating these first stars.Phil Schewe
