Supernovas Slosh Before Exploding   
       
   Feb. 19, 2014:  A longstanding mystery of astronomy, how supernovas explode,   
   might finally have been solved with the help of NASA's Nuclear Spectroscopic   
   Telescope Array (NuSTAR).  The high-energy X-ray observatory has mapped   
   radioactive material in the supernova remnant Cassiopeia A (Cas A).  The map   
   reveals how shock waves likely rip massive dying stars apart--by sloshing.   
       
   "Stars are spherical balls of gas, and so you might think that when they end   
   their lives and explode, that explosion would look like a uniform ball   
   expanding out with great power," said Fiona Harrison, the principal   
   investigator of NuSTAR at Caltech. "Our new results show how the explosion's   
   heart, or engine, is distorted, possibly because the inner regions literally   
   slosh around before detonating."   
       
   Harrison is a co-author of a paper about the results appearing in the Feb. 20   
   issue of Nature.   
       
   http://www.nasa.gov/jpl/nustar/pia17838/#.UwURyIWs8VA   
       
   In this false-color X-ray image of CAS A, blue traces the distribution of   
   radioactive titanium-44, which is produced in the heart of the supernova.     
   How supernovas explode has been a mystery for a long time: video. When   
   researchers simulate supernova blasts using computers, as a massive star dies   
   and collapses, the main shock wave often stalls out and the star fails to   
   shatter. The latest findings strongly suggest the exploding star literally   
   sloshed around, re-energizing the stalled shock wave and allowing the star to   
   finally blast off its outer layers.   
       
   NuSTAR's target, Cas A, was created when a massive star blew up as a supernova   
   leaving a dense stellar corpse and its ejected remains. The light from the   
   explosion reached Earth a few hundred years ago, so we are seeing the stellar   
   remnant when it was fresh and young.   
       
   "With NuSTAR we have a new forensic tool to investigate the explosion," said   
   the paper's lead author, Brian Grefenstette of Caltech. "Previously, it was   
   hard to interpret what was going on in Cas A because the material that we   
   could see only glows in X-rays when it's heated up. Now that we can see the   
   radioactive material, which glows in X-rays no matter what, we are getting a   
   more complete picture of what was going on at core of the explosion."   
       
   http://www.nasa.gov/jpl/nustar/pia17846/#.UwUZrYWs8VA   
       
   NuSTAR has helped decide between two competing models of supernova explosions:   
   Jets vs. Sloshing. MoreNuSTAR is the first telescope capable of producing maps   
   of radioactive elements in supernova remnants. In this case, the element is   
   titanium-44, which has an unstable nucleus produced at the heart of the   
   exploding star. The NuSTAR map of Cas A shows titanium concentrated in clumps   
   at the remnant's center, which suggests a sloshing action.   
       
   The NuSTAR map also casts doubt on other models of supernova explosions, in   
   which the star is rapidly rotating just before it dies and launches narrow   
   streams of gas that drive the stellar blast. Though imprints of jets have been   
   seen before around Cas A, it was not known if they were triggering the   
   explosion. NuSTAR did not see the titanium, essentially the radioactive ash   
   from the explosion, in narrow regions matching the jets, so the jets were not   
   the explosive trigger.   
       
   "This is why we built NuSTAR," said Paul Hertz, director of NASA's   
   astrophysics division in Washington. "To discover things we never knew -- and   
   did not expect -- about the high-energy universe."   
       
   Credits:   
   Production editor: Dr. Tony Phillips | Credit: Science@NASA   
       
   More information:   
   Why Won't the Supernova Explode?  -- this ScienceCast video explores the   
   longstanding mystery of supernova explosions   
       
   Supernovas seed the universe with many elements, including the gold in   
   jewelry, the calcium in bones and the iron in blood. While small stars like   
   our sun die less violent deaths, stars at least eight times as massive as our   
   sun blow up in supernova explosions. The high temperatures and particles   
   created in the blast fuse light elements together to create heavier elements.   
   Learn more   
       
   NuSTAR home page:   
   http://tinyurl.com/kaq8w66   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.99   
    * Origin: NCS BBS - Houma, LoUiSiAna (1:3828/7)