Sarah Keegan Headquarters, Washington, D.C. October 12, 1993 (Phone: 202/358-0883) Michael Finneran Goddard Space Flight Center, Greenbelt, Md. (Phone: 301/286-5565) RELEASE: 93-182 GAMMA-RAY OBSERVATORY PRODUCES THREE MAJOR DISCOVERIES NASA's Compton Gamma-Ray Observatory has yielded three major breakthroughs, two of which will enable scientists to unmask hidden supernovae -- the remnants of exploded stars -- buried deep in the center of the Milky Way. The third discovery pinpoints a source of the mysterious cosmic rays in this galaxy that have puzzled researchers since the rays first were detected more than 80 years ago. The findings were made by the Imaging Compton Telescope (COMPTEL), one of four instruments on the observatory, managed by NASA's Goddard Space Flight Center, Greenbelt, Md. "With these three observations, COMPTEL certainly has achieved a major breakthrough," said Dr. Volker Schoenfelder, of the Max Planck Institut in Germany and Principal Investigator for COMPTEL. The instrument is a collaborative project by Max Planck, the Space Research Organization of The Netherlands in Leiden, the European Space Agency's European Space Research and Technical Center in The Netherlands and the University of New Hampshire in Durham. "The first two observations are among the first quantitative tests of the whole theory of the origin of the elements in the universe, which are the building blocks upon which everything we are made of are created," Schoenfelder said. "The third discovery gives us a source for something that has eluded astrophysicists for more than 8 decades. So it's all quite exciting." Two of the COMPTEL discoveries were the detection of Titanium 44 and Aluminum 26 emissions called gamma-ray lines. Titanium 44 and Aluminum 26 were radioactive isotopes which, when they decayed, left an interstellar trail of crumbs that COMPTEL scientists traced to the supernovae that produced the emissions long ago. - more - - 2 - The Titanium 44 gamma-ray line was observed from the supernova remnant Cas-A, the leftover from a star that exploded in the mid-1600s some 9,000 light-years from Earth. A Titanium 44 gamma-ray line never had been observed by any space- or ground-based telescope until COMPTEL's powerful detector picked it up earlier this year. The isotope's relatively short half-life of 54 years -- the time it takes to radioactively decay into another chemical element -- means that scientists now will be able to look for Titanium 44 as evidence of comparatively recent supernovae that thus far, have eluded detection optically or with instruments that probe wavelengths in other than the visible spectrum. Such an ability is significant because observed supernovae in the Milky Way are rare compared to those sighted in other galaxies. Supernovae in other galaxies have been observed on average three times a century. By contrast, the last recorded supernova in the Milky Way was nearly 400 years ago, in 1604. Elements Will Serve As Beacons Researchers have speculated, however, that many more supernovae occur in the Milky Way but cannot be seen because of obscuring gas and dust that lies between Earth and the star-packed inner regions of the galaxy. "But with Titanium 44 as a beacon, COMPTEL and future experiments should be able to detect more of those hidden supernovae," said Schoenfelder. Unlike Titanium 44, Aluminum 26 emissions have been detected previously. Now COMPTEL scientists have found indications that link Aluminum 26 emissions to a supernova called Vela that took place some 10,000 years ago about 1,000 light-years away. If this finding is verified by further analysis, then COMPTEL would have, for the first time, established a link between Aluminum 26 emissions and a supernova. This in turn would allow scientists to discover more supernovae that occurred in the much more distant past, due to the very long half-life -- about 1 million years -- of Aluminum 26. COMPTEL's third discovery was to identify the Orion nebula, an area of molecular clouds and star-forming regions, as a source of cosmic rays. Cosmic rays are high-speed particles that fill the Milky Way galaxy. They were discovered in 1911, and scientists ever since have searched in vain for their sources. COMPTEL, however, identified a region in which cosmic rays are abundant. These cosmic rays were detected through their interaction with other particles in space. - more - - 3 - As the chemical elements that make up these rays were accelerated by supernovae explosions and stellar winds, the chemical elements collided with gas between stars in the Orion nebula at velocities up to the speed of light -- 186,000 miles per second. The collisions caused them to emit gamma-ray lines. COMPTEL detected gamma-ray lines for carbon and oxygen that were produced by these particle collisions. "It is now a challenge for theorists to explain what produces cosmic rays," said Schoenfelder. Most likely, they are created by the young stars in the Orion nebula. But no one is certain. The observatory was launched April 5, 1991, on the Space Shuttle Atlantis. It is managed by Goddard for the Office of Space Science, NASA Headquarters, Washington, D.C. - end -