The Mystery of Nanoflares   
       
   March 19, 2015:  When you attach the prefix "nano" to something, it usually   
   means "very small." Solar flares appear to be the exception.   
       
   Researchers are studying a type of explosion on the sun called a 'nanoflare.'    
   A billion times less energetic than ordinary flares, nanoflares have a power   
   that belies their name.   
       
   "A typical 'nanoflare' has the same energy as 240 megatons of TNT," says   
   physicist David Smith of UC Santa Cruz. "That would be something like 10,000   
   atomic fission bombs."   
       
   https://www.youtube.com/watch?v=wjB9JtTU7SU&feature=youtu.be   
       
   A new ScienceCast video explores the mystery of the sun's tiniest flares. Play   
   it   
       
   The sun can go days, weeks or even months without producing an ordinary solar   
   flare.  Nanoflares, on the other hand, are crackling on the sun almost   
   non-stop.   
       
   "They appear as little brightenings of the solar surface at extreme   
   ultraviolet and X-ray wavelengths," continues Smith. "The first sightings go   
   back to Skylab in the 1970s."   
       
   The relentless crackle of nanoflares might solve a long-standing mystery in   
   solar physics:  What causes the sun's corona to be so hot?   
       
   Imagine standing in front of a roaring fire.  You feel the warmth of the   
   flames.  Now back away.  You get cooler, right?   
       
   That's not how it works on the sun.  The visible surface of the sun has a   
   temperature of 5500 C.  Moving away from the surface should provide some   
   relief.  Instead, the sun's upper atmosphere, known as the "solar corona,"   
   sizzles at a million degrees--a temperature almost 200 times higher than that   
   of the roaring furnace below.   
       
   For more than a half-century, astronomers have tried to figure out what causes   
   the corona to be so hot.  Every year or so, a press release appears purporting   
   to solve the mystery, only to be shot down by a competing theory a year or so   
   later.  It is one of the most vexing problems in astrophysics.   
       
   http://www.nustar.caltech.edu/image/nustar141222a   
       
   X-rays stream off the sun in this image showing observations from by NASA's   
   Nuclear Spectroscopic Telescope Array, or NuSTAR, overlaid on a picture taken   
   by NASA's Solar Dynamics Observatory (SDO).  [more] Smith thinks nanoflares   
   might be involved. For one thing, they appear to be active throughout the   
   solar cycle, which would explain why the corona remains hot during Solar   
   Minimum.  And while each individual nanoflare falls short of the energy   
   required to heat the sun's atmosphere, collectively they might have no trouble   
   doing to job.   
       
   To investigate this possibility, Smith turned to a telescope designed to study   
   something completely different.   
       
   Launched in 2012, NASA's NuSTAR X-ray telescope is on a mission to study black   
   holes and other extreme objects in the distant cosmos. Solar scientists first   
   thought of using NuSTAR to study the sun about seven years ago, after the   
   space telescope's design and construction was underway. Smith contacted the   
   principal investigator, Fiona Harrison of the California Institute of   
   Technology in Pasadena, to see what she thought.   
       
   "At first I thought the whole idea was crazy," says Harrison. "Why would we   
   have the most sensitive high energy X-ray telescope ever built, designed to   
   peer deep into the universe, look at something in our own back yard?"   
       
   Eventually, she was convinced.  As Smith explained, NuSTAR has just the right   
   combination of sensitivity and resolution to study the telltale X-ray flickers   
   of nanoflares. A test image they took in late 2014 removed any doubt.  NuSTAR   
   turned toward the sun and, working together with NASA's Solar Dynamics   
   Observatory, captured one of the most beautiful images in the history of solar   
   astronomy.   
       
   The next step, says Smith, is to wait for Solar Minimum.  The current solar   
   cycle will wind down in the years ahead, leaving the sun mostly free of   
   sunspots and other magnetic clutter that can obscure nanoflares.  NuSTAR will   
   be able to survey the stellar surface and gather data on these explosions like   
   no telescope has done before.   
       
   Will it solve the mystery of nanoflares and the solar corona?  "I don't know,"   
   says Smith, "but I cannot wait to try."   
       
   Credits:   
   Author: Dr. Tony Phillips | Production editor: Dr. Tony Phillips | Credit:   
   Science@NASA   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.99   
    * Origin: NCS BBS - Houma, LoUiSiAna (1:3828/7)