A Star with Spiral Arms   
       
   Oct 31, 2011: For more than four hundred years, astronomers have used   
   telescopes to study the great variety of stars in our galaxy. Millions of   
   distant suns have been catalogued. There are dwarf stars, giant stars, dead   
   stars, exploding stars, binary stars; by now, you might suppose that every   
   kind of star in the Milky Way had been seen.   
       
   That's why a recent discovery is so surprising.  Researchers using the Subaru   
   telescope in Hawaii have found a star with spiral arms.   
       
   http://www.nasa.gov/images/content/597023main_SAO206462_dust_arms_labels_fina   
   l.jpg   
       
   Two spiral arms emerge from the gas-rich disk around SAO 206462, a young star   
   in the constellation Lupus. This image, acquired by the Subaru Telescope and   
   its HiCIAO instrument, is the first to show spiral arms in a circumstellar   
   disk. The disk itself is some 14 billion miles across, or about twice the size   
   of Pluto's orbit in our own solar system. (Credit: NAOJ/Subaru) [larger image]   
       
   The name of the star is SAO 206462.  It's a young star more than four hundred   
   light years from Earth in the constellation Lupus, the wolf.  SAO 206462   
   attracted attention because it has a circumstellar disk--that is, a broad disk   
   of dust and gas surrounding the star. Researchers strongly suspected that new   
   planets might be coalescing inside the disk, which is about twice as wide as   
   the orbit of Pluto.   
       
   When they took a closer look at SAO 206462 they found not planets, but arms.   
   Astronomers have seen spiral arms before: they're commonly found in pinwheel   
   galaxies where hundreds of millions of stars spiral together around a common   
   core.  Finding a clear case of spiral arms around an individual star, however,   
   is unprecedented1.   
       
   The arms might be a sign that planets are forming within the disk.   
       
   "Detailed computer simulations have shown us that the gravitational pull of a   
   planet inside a circumstellar disk can perturb gas and dust, creating spiral   
   arms," says Carol Grady, an astronomer with Eureka Scientific, Inc., who is   
   based at NASA's Goddard Space Flight Center. "Now, for the first time, we're   
   seeing these dynamical features."   
       
   Grady revealed the image to colleagues on Oct. 19th at a meeting at Goddard   
   entitled Signposts of Planets.   
       
   Theoretical models show that a single embedded planet may produce a spiral arm   
   on each side of a disk. The structures around SAO 206462, however, do not form   
   a matched pair, suggesting the presence of two unseen worlds, one for each arm.   
       
   Grady's research is part of a five-year international study of newborn stars   
   and planets using the giant 8.2 meter Subaru Telescope. Operated by the   
   National Astronomical Observatory of Japan, Subaru scans the heavens from a   
   perch almost 14,000 feet above sea level at the summit of the Hawaiian volcano   
   Mauna Kea. From there it has a crystal-clear view of innumerable young stars   
   and their planet-forming disks throughout the Milky Way.   
       
   "What we're finding is that once these systems reach ages of a few million   
   years-that's young for a star--their disks begin to show all kinds of   
   interesting shapes," says John Wisniewski, a collaborator at the University of   
   Washington in Seattle. "We've seen rings, divots, gaps--and now spiral   
   features. Many of these structures could be caused by planets moving within   
   the disks."   
       
   However, it is not an open and shut case. The research team cautions that   
   processes unrelated to planets might give rise to these structures. Until more   
   evidence is collected--or until the planets themselves are detected--they   
   can't be certain.   
       
   Whatever the cause of the arms, their reality is undeniable and the great   
   catalogue of stars has one more type.  Stay tuned to science@nasa for future   
   entries.   
       
       
   Author:Dr. Tony Phillips| Editor: Dr. Tony Phillips | Credit: Science@NASA   
       
   More Information   
   Subaru -- home page   
       
   Footnote: (1) "There have been other examples of circumstellar disks imaged   
   with partial spiral arms or blurry spiral arms," notes Marc Kuchner of   
   Goddard, who organized the conference. "So it's not completely unprecedented.   
   But this is really the first clear image of this phenomenon--clear enough that   
   you could trace the arms and possibly use them to make quantitative inferences   
   about what's causing them."   
       
      
   A video version of this story is available at:   
      
   http://www.youtube.com/watch?v=083fSbguKh8   
      
      
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.64   
    * Origin: NCS BBS (1:3828/7)