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    Zombie Star: Sol, This May Be Your Future
    By News Staff | November 15th 2012 04:02 PM | Print | E-mail | Track Comments
    The planetary nebula Abell 30 is located 5,500 light-years from Earth and it has given astronomers a lookl at a dying Sun-like star that came briefly back to life after giving up the stellar ghost, mimicking the possible fate our own Solar System faces in a few billion years.. 

     ‘Planetary nebula’ is the name given to the often-concentric shells of stellar material cast into space by dying stars. To astronomers of the 18th century, these objects looked like the colorful ‘blob’ of a planet through their telescopes, and the name stuck. Astronomers now know that as a star with less than eight times the mass of the Sun swells into a red giant towards the end of its life, its outer layers are expelled via pulsations and winds. 

     Ultraviolet radiation shining out from the stripped-down hot stellar core then lights up the ejected shells, resulting in intricate artworks that can be seen by modern telescopes.  The star at the heart of Abell 30 experienced its first brush with death 12,500 years ago, as seen from Earth, when its outer shell was stripped off by a slow and dense stellar wind. 

     Optical telescopes see the remnant of this evolutionary stage as a large, near-spherical shell of glowing material expanding out into space.  Then, about 850 years ago, the star suddenly came back to life, coughing out knots of helium and carbon-rich material in a violent event.  The star’s outer envelope briefly expanded during this born-again episode, but then very rapidly contracted again within 20 years. 



    A large spherical shell is seen in emission of hydrogen (blue) and oxygen (red) as the result of the star’s outer shell being stripped off by a dense wind and expanding outward over the last 12 500 years. During the ‘born-again’ phase in the star’s evolution, it expelled knots of helium and carbon-rich material. A subsequent fast wind is streaming past this material to form the flower-like structure seen in oxygen emission (red) to produce shock-heated gas seen in X-rays (purple). The inset panel zooms in to the heart of the planetary nebula to reveal intricate details closer to the star. The tail-like structures (orange) mark the dense knots of material from the ‘born-again’ event and are seen in HST images. X-ray emission from this evolutionary phase is shown in purple. The image spans approximately 2.5 x 2.5 arcminutes. Credits: Main image: X-ray: ESA/XMM-Newton; optical: NSF/NOAO/KPNO; inset: NASA/CXC/IAA-CSIC/M. Guerrero et al; optical: NASA/STScI

     This had the knock-on effect of accelerating the wind from the star to its present speed of 4,000 kilometers per second – over 14 million kilometers per hour. As this fast stellar wind catches up and interacts with the slower wind and clumps of previously ejected material, complex structures are formed, including the delicate comet-like tails seen near the central star in this image. 

     The stellar wind bombarding dense clumps of material provides a chilling look at the possible fate of Earth and its fellow planets in our own Solar System in a few billion years’ time.  

     When our Sun emits its final gasps of life at the heart of a planetary nebula, its strong stellar wind and harsh radiation will blast and evaporate any planets that may have survived the red giant phase of stellar evolution. If any distant civilization is watching with high-power telescopes at the time, they might see the glowing embers of the planets light up in X-rays as they are engulfed in the stellar wind.