Hello All!   
      
   Why Won't the Supernova Explode?    
      
   June 15, 2012: Somewhere in the Milky Way, a massive old star is about to die   
   a spectacular death. As its nuclear fuel runs out, the star begins to collapse   
   under its own tremendous weight. Crushing pressure triggers new nuclear   
   reactions, setting the stage for a terrifying blast. And then... nothing   
   happens.    
      
   At least that's what supercomputers have been telling astrophysicists for   
   decades. Many of the best computer models of supernovas fail to produce an   
   explosion. At the end of the simulation, gravity wins the day and the star   
   simply collapses.    
      
   Clearly, physicists are missing something.    
      
   http://www.youtube.com/watch?v=DVMwwKmF9NA   
      
   A new ScienceCast video explains how NASA's NuSTAR observatory will explore   
   the mystery of exploding stars. Play it.    
      
   "We don't fully understand how supernovas of massive stars work yet," says   
   Fiona Harrison, an astrophysicist at the California Institute of Technology.    
      
   To figure out what's going on, Harrison and colleagues would like to examine   
   the inside of a real supernova while it's exploding. That's not possible, so   
   they're doing the next best thing.    
      
   Using a telescope named "NuSTAR" --short for Nuclear Spectroscopic Telescope   
   Array -- they'll be scanning the debris from supernovas as soon as possible   
   after the blast.    
      
   http://science.nasa.gov/media/medialibrary/2010/01/07/07jan_nust   
   r_resources/su pernovamodel1.jpg   
      
   A supercomputer model of a spinning core-collapse supernova. NuSTAR   
   observations of actual supernova remnants will provide vital data for such   
   models. Credit: Fiona Harrison Launched over the Pacific Ocean on June 13,   
   2012, by a Pegasus XL rocket, NuSTAR is the first space telescope that can   
   focus very high-energy X-rays, producing images roughly 100 times sharper than   
   those possible with previous high-energy X-ray telescopes.    
      
   When NuSTAR finishes its check-out and becomes fully operational, scientists   
   will use it to scan supernovas for clues etched into the pattern of elements   
   spread throughout the explosion's debris.    
      
   "The distribution of the material in a supernova remnant tells you a lot about   
   the original explosion," says Harrison.    
      
   An element of particular interest is titanium-44. Creating this isotope of   
   titanium through nuclear fusion requires a certain combination of energy,   
   pressure, and raw materials. Inside the collapsing star, that combination   
   occurs at a depth that's very special. Everything below that depth succumbs to   
   gravity and collapses inward to form a black hole. Everything above that depth   
   will be blown outward in the explosion. Titanium-44 is created right at the   
   cusp.    
      
   So the pattern of how titanium-44 is spread throughout a supernova remnant can   
   reveal a lot about what happened at that crucial threshold during the   
   explosion. And with that information, scientists might be able to figure out   
   what's wrong with their computer simulations.    
      
   http://apod.nasa.gov/apod/ap050615.html   
      
   NuSTAR will map the distribution of titanium-44 in supernova remnants like   
   this one, Cassiopeia A, to search for evidence of asymmetries. Some scientists   
   believe the computer models are too symmetrical. Until recently, even with   
   powerful supercomputers, scientists have only been able to simulate a   
   one-dimensional sliver of the star. Scientists just assume that the rest of   
   the star behaves similarly, making the simulated implosion the same in all   
   radial directions.    
      
   But what if that assumption is wrong?    
      
   "Asymmetries could be the key," Harrison says. In an asymmetrical collapse,   
   outward forces could break through in some places even if the crush of gravity   
   is overpowering in others. Indeed, more recent, two-dimensional simulations   
   suggest that asymmetries could help solve the mystery of the "non-exploding   
   supernova."    
      
   If NuSTAR finds that titanium-44 is spread unevenly, it would be evidence that   
   the explosions themselves were also asymmetrical, Harrison explains.    
      
   To detect titanium-44, NuSTAR needs to be able to focus very high energy   
   X-rays. Titanium-44 is radioactive, and when it decays it releases photons   
   with an energy of 68 thousand electron volts. Existing X-ray space telescopes,   
   such as NASA's Chandra X-Ray Observatory, can focus X-rays only up to about 15   
   thousand electron volts.    
      
   Normal lenses can't focus X-rays at all. Glass bends X-rays only a miniscule   
   amount-not enough to form an image.    
      
   X-ray telescopes use an entirely different kind of "lens" consisting of many   
   concentric shells. They look a bit like the layers of a cylindrical onion.    
      
   http://www.nustar.caltech.edu/about-nustar/instrumentation/optics   
      
   The x-ray "light path" of the EPIC camera of the XMM-Newton satellite, a   
   design similar to that used by NuSTAR. Credit: ESA/ESTEC. [more]    
      
   Incoming X-rays pass between these layers, which guide the X-rays to the focal   
   surface. It's not a lens, strictly speaking, because the X-rays reflect off   
   the surfaces of the shells instead of passing through them, but the end result   
   is the same.    
      
   The NuSTAR team has spent years perfecting delicate manufacturing techniques   
   required to make high-precision X-ray optics for NuSTAR that work at energies   
   as high as 79 thousand electron volts.    
      
   Their efforts could end up answering the question, "Why won't the supernova   
   explode?"1   
      
      
   Authors: Patrick Barry, Dr. Tony Phillips| Production editor: Dr. Tony   
   Phillips | Credit: Science@NASA   
      
   More Information    
   1Supernova research is just for starters. NuSTAR will also study black holes,   
   blazars, pulsars, and many more exotic objects. The high-energy Universe is   
   about to come into sharper focus-and no one can say what surprises may be in   
   store.    
      
   NuSTAR home page -- from Caltech    
      
   NASA's NuSTAR Mission Lifts Off -- NASA press release    
      
      
      
   Regards,   
      
   Roger    
   --- timEd/386 1.10.y2k+   
    * Origin: NCS BBS - Houma, LA - (1:3828/7)