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Antimatter Clouds and Fountain
Discovered in the Milky Way

Positrons and antimatter cloud at the center of the Milky Way galaxy
Scientists have discovered a hot fountain of gas filled with antimatter electrons spewing out of the center of our Milky Way galaxy.

NASA's orbiting Compton Gamma Ray Observatory (CGRO) spacecraft spotted two unexpected clouds of antimatter in the Milky Way Galaxy. The clouds suggest a hot fountain of gas filled with antimatter electrons is rising from the region around the center of the our galaxy. Antimatter electrons also are known as positrons.

The nature of the furious activity producing the hot antimatter-filled fountain is unclear, but could be related to massive numbers of stars being born near the large black hole at the center of our galaxy. Other possibilities include winds from giant stars or black hole antimatter factories.

Scintillation spectrometer

Scientists from Northwestern University at Evanston, Illinois, the Naval Research Laboratory (NRL) at Washington, DC, and other research institutions, used a CGRO instrument known as the Oriented Scintillation Spectrometer Experiment (OSSE) to discover what the researchers call "antimatter annihilation radiation."

Surprisingly, CGRO's maps of gamma ray sources, which they had expected to show a large cloud of antimatter near the galactic center and along the plane of the galaxy, also showed a second cloud of antimatter well off the galactic plane. That second cloud may have been 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," according to 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, Virgina, on April 28, 1997. The results have been submitted for publication in the Astrophysical Journal.

A new room in the house

A second paper presented at the conference, titled "The Annihilation Fountain in the Galactic Center Region," authored by Dr. Charles Dermer and Dr. Jeffrey Skibo of NRL, examines theoretical models for one possible source of the antimatter -- star bursts in the central region. They noted 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, 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," Dermer said. "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."

The Milky Way black hole

Evidence points to the existence of a black hole with the mass of a million Suns at the very center of our galaxy. Unlike 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 birth, 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 -- holds that such outflowing jets could be made of antimatter.

Gamma rays

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.

Compton Gamma Ray Observatory

Launched into Earth orbit from space shuttle Atlantis in 1991, the Compton Gamma Ray Observatory is the second of NASA's "Great Observatories." CGRO views the universe in a search for gamma rays and their source.

Using the OSSE experiment, the team found antimatter positrons 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 researchers favor the idea that freshly synthesized radioactive material in stellar explosions is being ejected up above our galaxy in an annihilating fountain of gas. Dermer and Skibo say they like that scenario because exploding stars eject large quantities of hot gas made up of normal matter. That hot gas provides a target with which antimatter electrons can annihilate.

CGRO Images

CGRO images are available on the World Wide Web.

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