SETI [ASTRO] New Findings Narrow Theories On Cosmic Ray Origin


Larry Klaes (lklaes@bbn.com)
Wed, 02 Jun 1999 14:42:15 -0400


>X-Authentication-Warning: brickbat12.mindspring.com: majordom set sender to owner-astro using -f >Date: Tue, 1 Jun 1999 14:42:14 GMT >From: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov> >To: astro@lists.mindspring.com >Subject: [ASTRO] New Findings Narrow Theories On Cosmic Ray Origin >Sender: owner-astro@brickbat12.mindspring.com >Reply-To: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov> > >Bill Steigerwald >Goddard Space Flight Center May 31, 1999 >Greenbelt, MD >wsteiger@pop100.gsfc.nasa.gov >(Phone: 301-286-5017) > >RELEASE NO: 99-070 > >NEW FINDINGS NARROW THEORIES ON COSMIC RAY ORIGIN > >Where do those fast-flying atoms that pelt the Earth come from? Scientists >catching cosmic rays with a NASA spacecraft have tightened the constraints >on the evolving theory of how atoms travelling at nearly the speed of light >are produced in stars and are strewn across the Universe through star >explosions, or supernovae. > >Cosmic rays bombard the Earth's atmosphere constantly. These highly >energetic particles are not "rays," however, but rather atoms that were >stripped of their electrons when they were accelerated to enormous speeds. >While many scientists agree that the energy of supernovae is needed to >produce cosmic rays, debates rage over the "seed particles," or the actual >atoms that are being accelerated. Are the particles accelerated directly >from a supernova, like shrapnel in an explosion? Or are they from dust and >gas already present in the region between stars, bumped to high speeds by >the blast wave of a supernova explosion? > >Results from NASA's Advanced Composition Explorer (ACE) suggest that >cosmic rays are not accelerated directly from supernovae, as some current >models predict. Rather, it is material that has been sitting around for >hundreds of thousands of years that gets accelerated by the shock wave of >a supernova explosion. > >Dr. Paul Hink of Washington University in St. Louis (WUSL) and a team of >scientists from WUSL, California Institute of Technology, NASA's Jet >Propulsion Laboratory and NASA's Goddard Space Flight Center present >these results from the ACE Cosmic Ray Isotope Spectrometer (CRIS) at the >Centennial Meeting of the American Astronomical Society in Chicago on May >31, 1999. > >CRIS scientists analyzed cosmic rays from the elements nickel (Ni) and >cobalt (Co). The radioactive isotope Ni-59, which is produced in supernova >explosions, ultimately decays into the more stable Co-59; the half-life is >75,000 years. Hink said the team found in their cosmic ray collection that >this decay process had already run its course. This means that Ni-59, formed >in one supernova explosion, sat decaying for over a 100,000 years before >another supernova blast wave came along and propelled it into the >surrounding galaxy at cosmic ray energies. > >If the supernova itself accelerated the freshly-made Ni-59 to cosmic ray >energies, Hink said, then the CRIS scientists would have seen more Ni-59 >in their cosmic ray collection, and less Co-59. Team members ruled out the >possibility of Ni-59 decaying while en-route to Earth, because in order to >decay, the Ni-59 nucleus has to absorb one of its electrons. Hink said that >once an atom of Ni-59 is accelerated to cosmic ray energies and loses its >electrons, it is relatively stable and invulnerable to decay, as long as it >keeps moving. > >Dr. Mark Wiedenbeck of NASA's Jet Propulsion Laboratory, a member of the >CRIS team, said their results rule out the possibility of the cosmic ray >seed particles being fresh supernova ejecta. Instead, the results support >theories for the origin of cosmic rays to be old stellar or interstellar >material. Results are also consistent with the superbubble theory, put forth >last year. According to this theory, a succession of supernovae carve out a >superbubble, or a cavity within a giant molecular cloud in our galaxy, in >which the seed particles of cosmic rays, produced directly by the >supernovae, can linger (and decay) for millions of years before breaking >out of the bubble and being accelerated to cosmic ray energies. > >CRIS was developed by the California Institute of Technology, Washington >University in St. Louis, Goddard Space Flight Center, and the Jet Propulsion >Laboratory. The instrument is one of nine aboard ACE, launched by NASA in >1997 to collect and analyze matter from the sun, from the space between >planets and from the Milky Way galaxy beyond our solar system. > >EDITOR'S NOTE: Images to support this story are available on the web at: > ftp://PAO.GSFC.NASA.GOV/newsmedia/AAS/ACE > >



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