Milky Way Blows Bubbles ?!
Astronomers using the NASA's Compton Gamma-Ray Observatory (CGRO) satellite to
map the distribution of antimatter in the Milky Way Galaxy were
surprised to find what appears to be a large antimatter
bubble being blown upward from the center of our Galaxy.
Matter is made up of the basic atomic
building blocks of protons, neutrons and electrons. Antimatter
particles are exact duplicates of particles but with opposite
properties. For instance, a positron, the antiparticle of the
electron, carries an equal, but opposite charge (the electron
is negatively charged, the positron is positively charged).
When an electron and positron encounter one another they
annihilate, converting the mass of both particles completely
into energy which we detect as gamma-ray emission at the specific energy
of 511 keV. Since the 1970s, astronomers have seen the tell-tale sign
of antimatter in the galactic center: a significant emission feature at
exactly the right energy.
Matter is far more common in the observable Universe
than antimatter, which is rarely observed. Antiparticles can
be created from radioactive decay processes, and by
matter falling into a black hole. A massive black hole is
believed to exist at the center of the Milky Way Galaxy, and
could be responsible for generating the positrons that give
rise to the 511 keV emission when they interact with and
The surprising result from the CGRO instrument OSSE was not the detection
of this annihilation radiation, but how it is distributed in our Galaxy.
According to all previous theoretical models, it was expected that 511 keV
emission would be seen at the galactic center and along the plane of the
Galaxy. However, the OSSE results, which were released April 28, 1997 at the
4th CGRO Symposium in Williamsburg, VA, showed a large cloud of radiation
emanating from the galactic center, perpendicular to the disk.
The origin of this newly discovered cloud of antimatter is a mystery.
"The antimatter cloud could have been formed by multiple star bursts
occurring in the central region of the Galaxy, jets of material from a black
hole near the Galactic center, the merger of two neutron stars, or it could
have been produced by an entirely different source," said James D. Kurfess,
head of the Gamma and Cosmic Ray Astrophysics Branch at the Naval Research
Laboratory. It's a sure bet that theorists will be studying these new
results, and others that will follow, to shed light on the mystery of
the antimatter bubble.
Our old home Galaxy has a whole new look now, thanks
to astronomers taking a look at it in gamma-rays.