Hubble Sees the Fireball from a "Kilonova"   
       
   August 3, 2013:  NASA's Hubble Space Telescope has detected a new kind of   
   stellar blast called a kilonova, which happens when a pair of compact objects   
   such as neutron stars crash together.  Hubble observed the fading fireball   
   from a kilonova last month, following a short gamma ray burst (GRB) in a   
   galaxy almost 4 billion light-years from Earth.   
       
   "This observation finally solves the mystery of short gamma ray bursts," says   
   Nial Tanvir of the University of Leicester in the United Kingdom, who led a   
   team of researchers conducting this research.   
       
   http://hubblesite.org/newscenter/archive/releases/2013/29/image/e/   
       
   This sequence illustrates the kilonova model for the formation of a   
   short-duration gamma-ray burst. 1. A pair of neutron stars in a binary system   
   spiral together. 2. In the final milliseconds, as the two objects merge, they   
   kick out highly radioactive material. This material heats up and expands,   
   emitting a burst of light called a kilonova. 3. The fading fireball blocks   
   visible light but radiates in infrared light. 4. A remnant disk of debris   
   surrounds the merged object, which may have collapsed to form a black hole.   
   More   
       
   Gamma ray bursts are flashes of intense high-energy radiation that appear from   
   random directions in space.  They  come in two flavors--long and short.  "Many   
   astronomers, including our group, have already provided a great deal of   
   evidence that long-duration gamma ray bursts (those lasting more than two   
   seconds) are produced by the collapse of extremely massive stars," explains   
   Tanvir.   
       
   The short bursts, however, were more mysterious.   
       
   "We only had weak circumstantial evidence that short bursts [might be]   
   produced by the merger of compact objects," he adds. "This result now appears   
   to provide definitive proof."   
       
   Astrophysicists have predicted short-duration GRBs are created when a pair of   
   super-dense neutron stars in a binary system spiral together. This event   
   happens as the system emits gravitational radiation, creating tiny waves in   
   the fabric of space-time. The energy dissipated by the waves causes the two   
   stars to sweep closer together. In the final milliseconds before the   
   explosion, the two stars merge into a death spiral that kicks out highly   
   radioactive material. This material heats up and expands, emitting a burst of   
   light.   
       
   The resulting "kilonova" is about 1,000 times brighter than a regular nova,   
   which is caused by the eruption of a white dwarf.   
       
   http://hubblesite.org/newscenter/archive/releases/2013/29/image/a/   
       
   These Hubble images show the fireball afterglow of Gamma-ray Burst 130603B.   
   More   
       
   In a recent science paper Jennifer Barnes and Daniel Kasen of the University   
   of California at Berkeley and the Lawrence Berkeley National Laboratory   
   presented new calculations predicting how kilonovas should look. They   
   predicted the same hot plasma producing the radiation also will block the   
   visible light, causing the gusher of energy from the kilonova to flood out in   
   near-infrared light over several days.   
       
   An unexpected opportunity to test this model came June 3 when NASA' s Swift   
   space telescope picked up the extremely bright gamma ray burst, cataloged as   
   GRB 130603B. Although the initial blast of gamma rays lasted just one-tenth of   
   a second, it was roughly 100 billion times brighter than the subsequent   
   kilonova flash.   
       
   From June 12-13, Hubble searched the location of the initial burst, spotting a   
   faint red object. An independent analysis of the data from another research   
   team confirmed the detection. Subsequent Hubble observations on July 3   
   revealed the source had faded away, therefore providing the key evidence the   
   infrared glow was from an explosion accompanying the merger of two objects.   
       
   The team's results appeared Aug. 3 in a special online publication of the   
   journal Nature.   
       
   Credits:   
       
   Production editor: Dr. Tony Phillips | Credit: Science@NASA   
       
   More information:   
       
   For images and more information on the kilonova, visit: http://h   
   bblesite.org/news/2013/29   
       
   For more information about the Hubble Space Telescope, visit: ht   
   p://www.nasa.gov/hubble   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.94   
    * Origin: NCS BBS - Houma, LoUiSiAna (1:3828/7)