January 13, 2008

Source of Mysterious Antimatter Found

which annihilates matter upon contact, seems to be rare in the universe. Still,
for decades, scientists had clues that a vast cloud of antimatter lurked in
space, but they did not know where it came from.

mysterious source of this antimatter has now been discovered — stars getting ripped
apart by neutron stars and black

antimatter propulsion systems are so far the stuff of science fiction,
antimatter is very real.

What it is

elementary particles, such as protons and electrons, have antimatter
counterparts with the same mass but the opposite charge. For instance, the
antimatter opposite of an electron, known as a positron, is positively charged.

a particle meets its antiparticle, they destroy each other, releasing a burst
of energy such as gamma
. In 1978, gamma ray detectors flown on balloons detected a type of gamma
ray emerging from space that is known to be emitted when electrons collide with
positrons — meaning there was antimatter in space.

was quite a surprise back then to discover part of the universe was made of
antimatter," researcher Gerry Skinner, an astrophysicist at Goddard Space
Flight Center in Greenbelt, Md., told SPACE.com.

gamma rays apparently came from a cloud of antimatter roughly 10,000 light-years
across surrounding our galaxy's core. This giant cloud shines brightly with
gamma rays, with about the energy of 10,000 suns.

exactly generated the antimatter was a mystery for the following decades.
Suspects have included everything from exploding stars to dark

an international research team looking over four years of data from the
European Space Agency's International Gamma Ray Astrophysics Laboratory
(INTEGRAL) satellite has pinpointed the apparent culprits. Their new findings
suggest these positrons originate mainly from stars getting devoured by black
holes and neutron stars.

a black hole or neutron star destroys a star, tremendous amounts of radiation are
released. Just as electrons and positrons emit the tell-tale gamma rays upon
annihilation, so too can gamma rays combine to form electrons and positrons, providing
the mechanism for the creation of the antimatter cloud, scientists think.

Billions and billions

researchers calculate that a relatively ordinary star getting torn apart by a
black hole or neutron star
orbiting around it — a so-called "low mass X-ray binary" — could spew
on the order of one hundred thousand billion billion billion billion positrons
(a 1 followed by 41 zeroes) per second. These could account for a great deal of
the antimatter that scientists have inferred, reducing or potentially
eliminating the need for exotic explanations such as ones involving dark

estimates suggest that about half and possibly all the antimatter is coming
from X-ray binaries," said researcher Georg Weidenspointner of the Max
Planck Institute for Extraterrestrial Physics in Germany.

that they have witnessed the death of antimatter, the scientists hope to see its

would be interesting if black holes produced more matter than neutron stars, or
vice versa, although it's too early to say one way or the other right
now," Skinner explained. "It can be surprisingly hard to tell the
difference between an X-ray binaries that hold black holes and neutron

Skinner and their colleagues, detailed their findings in the Jan. 10 issue of
the journal Nature.