The Annihilation Fountain in the Galactic Center Region

Interpreting the Cloud - A companion release to NRL Press Release 31-97R

An unexpected cloud of antimatter annihilation radiation was discovered by a team led by Naval Research Laboratory (NRL) and Northwestern University researchers using data obtained with the Oriented Scintillation Spectrometer Experiment (OSSE) on the Compton Gamma Ray Observatory. This discovery points to the existence of a hot fountain of gas filled with antimatter electrons rising from a region that surrounds the center of our galaxy. The nature of the furious activity producing the hot antimatter-filled fountain is unclear, but could be related to prolific star formation taking place near the large black hole at our galaxy's center. Other possibilities include winds from overweight stars or black hole antimatter factories.

The interpretation of this major discovery is presented at the Fourth Compton Symposium in Williamsburg, Virginia on Monday, April 28th by Drs. Charles Dermer and Jeffrey Skibo, both 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, 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."

Background

We live on the outskirts of an undistinguished spiral galaxy called the Milky Way. Our Solar System lies over 25,000 light years from our galaxy's center, which is blocked from the view of optical telescopes by intervening gas and dust. Yet we can still look at the inner parts of our galaxy by peering with telescopes sensitive at radio, infrared, X-ray and gamma-ray wavelengths.

Evidence points to the existence of a black hole with the mass of a million Suns at the very
center of our galaxy. Strangely enough, unlike in other galaxies which harbor huge black holes,
very little light comes from this source. Some 300 light years from the galactic center lies another black hole called the Great Annihilator which, though weighing in at only 10-100 times the mass of the Sun, produces X-rays and jets seen by their radio emissions. The outflowing jets could be made of antimatter. 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.

In 1991, NASA launched the Compton Gamma Ray Observatory. One of its goals was to view our galaxy in the light of gamma rays. Gamma rays are extremely energetic light photons produced by high-energy particles, by the decay of excited nuclei, and also produced when matter annihilates with antimatter. Antimatter cannot be found in large quantities on Earth because it would instantly vaporize anything it came into contact with. All evidence points to our universe being composed almost entirely of normal matter, though opinions differ on this. It was therefore unexpected to find a cloud of annihilating antimatter above the center of our galaxy.

Using OSSE on the Compton Observatory, developed by a team led by Dr. James Kurfess of NRL, antimatter positrons were found 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 spewn 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.

Whatever the true situation, a hot gas appears to be heated and blown out from the region near the center of our galaxy. This antimatter-filled gas traces a new feature of our Milky Way, essentially unknown until now. Activity hidden behind vast clouds of dust and gas can be seen in the light of its gamma radiation, giving us a new view of our home galaxy.

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A full set of figures may be found here.

Fountain Simulation caption: Theoretical model of the fountain of annihilating antimatter electrons. The broad horizontal emissision is annihilation radiation from the disk of the galaxy. The bright circular region is annihilation radiation from the galactic center. The newly discovered fountain of annihilation radiation points upward, away from the plane of the galaxy.

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