Paula Cleggett-Haleim
Headquarters, Washington, D.C.

Embargoed Until
(Phone: 202/358-0883) 2:30
p.m. EDT, June 7, 1993


Randee Exler
Goddard Spaceflight Center, Greenbelt, Md. (Phone: 301/286-0697)


Release: 93-105

NEW DISCOVERIES BY NASA'S EUV EXPLORER PRESENTED

   Recent discoveries from NASA's Extreme Ultraviolet Explorer (EUVE) will be presented June 7 and 8, 1993, at the 182nd National Meeting of the American Astronomical Society (AAS), University of California at Berkeley following the 1-year anniversary of EUVE's launch.

   The new results include discovery of elements that blanket the light from white dwarf stars, the detection of ionized helium in the local interstellar gas, the detection of an extreme ultraviolet shadow in the local interstellar medium and new findings on the mysteries of rare extragalactic objects.

   The astronomers will discuss why hot white dwarf stars emit only small amounts of extreme ultraviolet radiation, despite that their high temperatures should make them produce large amounts of EUV radiation. EUVE data reveal that unexpected elements - mostly iron - may work as a blanket which blocks the EUV radiation and prevent it from escaping into space.

   This information promises important new results about the evolution of stars into the white-dwarf stage and may help astronomers calculate the details of how stars age and die, as our the sun will die when it becomes a white dwarf in about 5 billion years, according to the astronomers.

   What physical conditions describe the gas surrounding this solar system? The EUVE has allowed astronomers for the first time to observe ionized helium (helium atoms that have lost one of their two electrons) in the gas that floats among the sun and nearby stars. The EUVE satellite's observations may soon yield far better measurements of the density, temperature and ionization state of this interstellar gas than have been possible until now.

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   The Deep Survey Telescope on board EUVE has obtained the first direct evidence that the gas and dust drifting among the stars in this galaxy emit a faint glow in the EUV. EUVE observed an EUV "shadow" cast by this gas and dust cloud. The cloud lies in the direction of the constellation Taurus and is believed to be approximately 200 light-years away. Its location indicates to astronomers that the hot, ionized gas of the local interstellar medium extends much farther than previously thought.

Unraveling the Nature of Extragalactic Objects

   The first sky survey ever conducted in the entire EUV band of the electromagnetic spectrum has revealed that some of the rarest, most exotic objects in the universe -- BL Lacertae Objects (BL Lacs) -- are surprisingly visible in the EUV. The finding, which will be discussed at this meeting, brings scientists one step closer to puzzling out the mysterious nature of BL Lacs.

   BL Lacs are comparatively rare and are theorized to be centered on massive black holes. By analyzing the EUV light given off by these objects, scientists may learn more about the composition and velocities of matter entering possible black holes.

   Active galactic nuclei (AGN) are another class of rare extragalactic objects to be discussed at this meeting. Many of the AGNs seen in previous surveys either were detected weakly or not observed at all in the EUV. EUVE has revealed that some AGNs are visible in the EUV because their central source of energy is powerful enough to clear a path through the surrounding, otherwise opaque neutral gas.

   The EUVE was launched June 7, 1992 to make the first survey of the universe at all the wavelengths contained in the EUV band of the spectrum. The Center for Extreme Ultraviolet Astrophysics (CEA), under contract to NASA's Goddard Space Flight Center, Greenbelt, Md., serves as the Science Operations and Data Analysis Facility for EUVE. EUVE is part of NASA's Office of Space Science's Explorer program in Washington, D.C.

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EDITORS NOTE
Guest observers and astronomers from the CEA in Berkely will present the new results during a press conference on June 7 at 2:30 p.m. EDT. The AAS press room, located in the West Madrone Room, Student Union, University of California at Berkeley, opens 1 p.m., June 6. Media needing assistance may call (510) 643-7070, -7120 or -7137.



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