A mysterious object that seems to defy classification has been found by astronomers using NASA's Hubble Space Telescope. The image is available online at:
The object looks like a young, dust-enshrouded star with narrow jets of material resembling strings of beads streaming from each side. It has been classified as a planetary nebula, the glowing remains of a Sun-like star in its death throes, although the Hubble observations suggest it may not fit that classification, either.
The Hubble astronomers, Dr. Raghvendra Sahai of NASA's Jet Propulsion Laboratory, Pasadena, Calif., and Lars-Ake Nyman of the European Southern Observatory, Chile, and Onsala Space Observatory, Sweden, suspect this enigmatic object, known as He2- 90, may be a pair of aging stars masquerading as a single youngster. One member of the duo is a bloated red giant star shedding matter from its outer layers. This matter is then captured by gravity in a rotating accretion disk around a compact partner, most likely a young white dwarf (the collapsed remnant of a Sun-like star). The stars are not visible in the Hubble images because they're obscured by a disk of dust.
Each jet has at least six bright clumps of gas speeding away at estimated rates of at least 600,000 kilometers an hour (375,000 miles an hour) and extending at least 100,000 astronomical units (one astronomical unit equals the Earth-Sun distance of 150 million kilometers or 93 million miles). These gaseous clumps are ejected into space about every 100 years and may be caused by periodic instabilities in He2-90's accretion disk. Astronomers believe that magnetic fields associated with accretion disks produce and constrict the pencil-thin jets.
This oddball star was discovered during an imaging survey of planetary nebulae. The images were taken Sept. 28, 1999 with Hubble's Wide Field and Planetary Camera 2, designed and built by JPL. The images and results appear in the Aug. 1 issue of the Astrophysical Journal Letters.
The Space Telescope Science Institute, Baltimore, Md, manages space operations for the Hubble Space Telescope for NASA's Office of Space Science, Washington, D.C. The Institute is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract with NASA's Goddard Space Flight Center, Greenbelt, Md. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency.
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