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ANTIMATTER CLOUDS AND FOUNTAIN DISCOVERED IN THE MILKY
WAY
Scientists using data from an instrument on
NASAOs Compton Gamma Ray Observatory (CGRO) have
discovered two unexpected clouds of antimatter in the
Milky Way Galaxy which scientists call Oantimatter
annihilation radiation.O
Scientists from Northwestern University,
Evanston, IL, the Naval Research Laboratory (NRL),
Washington, DC, and other institutions used CGROOs
Oriented Scintillation Spectrometer Experiment (OSSE)
to make the discovery, which points to the existence
of a hot fountain of gas filled with antimatter
electrons rising from a region that surrounds the
center of the Milky Way galaxy. The nature of the
furious activity producing the hot antimatter-filled
fountain is unclear, but could be related to massive
star formation taking place near the large black hole
at the center of the galaxy. Other possibilities
include winds from giant stars or black hole
antimatter factories.
The researchers used maps of gamma ray sources
from CGRO which they expected to show a large cloud of
antimatter near the galactic center and along the
plane of the galaxy. The maps, surprisingly, also
show a second cloud of antimatter well off the
galactic plane. The second cloud may be caused by the
explosions of young massive stars.
"The origin of this new and unexpected source
of antimatter is a mystery," said William R. Purcell,
research scientist and assistant professor of physics
and astronomy at Northwestern University.
"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.
The researchers presented their findings today
at the fourth Compton Symposium in Williamsburg, VA.
The results have been submitted for publication in the
Astrophysical Journal. A second paper presented at
the conference, titled "The Annihilation Fountain in
the Galactic Center Region," examines theoretical
models for one possible source of the antimatter --
star bursts in the central region.
The second paper is authored by Dr. Charles
Dermer and Dr. Jeffrey Skibo of NRL. They note that
the gamma-ray observations permit us to see clearly,
for the first time, a new part of our galaxy made of a
hot column of gas filled with antimatter electrons
(also called positrons by scientists), and they argue
that the antimatter electrons come from newly created
elements produced by exploding stars formed near the
center of our galaxy.
"It is like finding a new room in the house we
have lived in since childhood," comments Dr. Dermer.
"And the room is not empty -- it has some engine or
boiler making hot gas filled with annihilating
antimatter. No one is certain whether the antimatter
comes from exploding stars, black holes or something
entirely different, and that is what makes this
discovery so exciting."
Evidence points to the existence of a black
hole with the mass of a million Suns at the very
center of our galaxy. Unlike in other galaxies which
harbor huge black holes, very little light comes from
this source. Huge dense clouds of gas also surround
the galactic center. Prolific star formation,
powerful stellar winds from massive stars, and
supernovae are all found here. Another theory, based
on observation of radio emissions showing some black
holes produce X-rays and jets, is that such outflowing
jets could be made of antimatter.
The Compton Gamma Ray Observatory, launched
from the Space Shuttle in 1991, views the universe in
a search for gamma rays and their source. Gamma rays
are extremely energetic light photons produced by
high-energy particles, by the decay of excited nuclei,
and when matter and antimatter annihilate each other.
Antimatter cannot be found in large quantities on
Earth because it would instantly vaporize anything it
came into contact with. All evidence points to the
universe being composed almost entirely of normal
matter, though opinions differ on this.
Using the OSSE experiment, the OSSE team found
antimatter positrons to be annihilating with normal
matter electrons at an astonishing rate. Scientists
are speculating on the origin of this antimatter, with
a "black-hole lobby" favoring antimatter production in
the jets of black holes.
Other scientists favor freshly synthesized
radioactive material in stellar explosions being
ejected up above our galaxy in an annihilating
fountain of gas. Drs. Dermer and Skibo favor the
latter scenario, because exploding stars will eject
large quantities of hot gas made up of normal matter.
This hot gas provides a target with which the
antimatter electrons can annihilate.
Related images may be obtained via the World Wide Web
at URL:
http://www.astro.nwu.edu/aetro/purcell/511kev_presa_re
lesse
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