Dark Fireworks on the Sun   
       
   July 11, 2011: On June 7, 2011, Earth-orbiting satellites detected a flash of   
   X-rays coming from the western edge of the solar disk. Registering only "M"   
   (for medium) on the Richter scale of solar flares, the blast at first appeared   
   to be a run-of-the-mill eruption--that is, until researchers looked at the   
   movies.   
       
   "We'd never seen anything like it," says Alex Young, a solar physicist at the   
   Goddard Space Flight Center. "Half of the sun appeared to be blowing itself to   
   bits."   
       
   NASA has just released new high-resolution videos of the event recorded by the   
   Solar Dynamics Observatory (SDO). The videos are large, typically 50 MB to 100   
   MB, but worth the wait to download. Click on the arrow to launch the first   
   movie, then scroll down for commentary:   
   [...]   
   A close-up of the June 7th eruption shows dark blobs of plasma falling   
   ballistically toward the surface of the sun. [99 MB Quicktime] [more]   
       
   "IN terms of raw power, this really was just a medium-sized eruption," says   
   Young, "but it had a uniquely dramatic appearance caused by all the inky-dark   
   material. We don't usually see that."   
       
   Solar physicist Angelos Vourlidas of the Naval Research Lab in Washington DC   
   calls it a case of "dark fireworks."   
       
   "The blast was triggered by an unstable magnetic filament near the sun's   
   surface," he explains. "That filament was loaded down with cool1 plasma, which   
   exploded in a spray of dark blobs and streamers."   
   [...]   
   Plasma blobs are funneled toward sunspots by magnetic fields. [67 MB   
   Quicktime] [more]   
       
   The plasma blobs were as big as planets, many larger than Earth. They rose and   
   fell ballistically, moving under the influence of the sun's gravity like balls   
   tossed in the air, exploding "like bombs" when they hit the stellar surface.   
       
   Some blobs, however, were more like guided missiles. "In the movies we can see   
   material 'grabbed' by magnetic fields and funneled toward sunspot groups   
   hundreds of thousands of kilometers away," notes Young.   
       
   SDO also detected a shadowy shock wave issuing from the blast site. The 'solar   
   tsunami' propagated more than halfway across the sun, visibly shaking   
   filaments and loops of magnetism en route. [91 MB Quicktime]   
       
   Long-range action has become a key theme of solar physics since SDO was   
   launched in 2010. The observatory frequently sees explosions in one part of   
   the sun affecting other parts. Sometimes one explosion will trigger another   
   ... and another ... with a domino sequence of flares going off all around the   
   star.   
       
   "The June 7th blast didn't seem to trigger any big secondary explosions, but   
   it was certainly felt far and wide," says Young.   
   [...]   
   This 13 MB extreme ultraviolet movie of the explosion shows a 'solar tsunami'   
   wave billowing away from the blast site. [13 MB Quicktime] [more]   
   It's tempting to look at the movies and conclude that most of the exploded   
   material fell back--but that wouldn't be true, according to Vourlidas. "The   
   blast also propelled a significant coronal mass ejection (CME) out of the   
   sun's atmosphere."   
       
   He estimates that the cloud massed about 4.5 x1015 grams, placing it in the   
   top 5% of all CMEs recorded in the Space Age. For comparison, the most massive   
   CME ever recorded was 1016 grams, only a factor of ~2 greater than the June   
   7th cloud.2 The amount of material that fell back to the sun on June 7th was   
   approximately equal to the amount that flew away, Vourlidas says.   
       
   As remarkable as the June 7th eruption seems to be, Young says it might not be   
   so rare. "In fact," he says, "it might be downright common."   
       
   Before SDO, space-based observatories observed the sun with relatively slow   
   cadences and/or limited fields of view. They could have easily missed the   
   majesty of such an explosion, catching only a single off-center snapshot at   
   the beginning or end of the blast to hint at what actually happened.   
       
   If Young is right, more dark fireworks could be in the offing.  Stay tuned.   
       
       
   Author: Dr. Tony Phillips | Credit: Science@NASA   
       
   More Information   
   Footnotes:   
       
   1"Cool" has a special meaning on the sun: The plasma blobs registered a   
   temperature of 20,000 K or less. That is relatively cool. Most of the   
   surrounding gas had temperatures between 40,000 K and 1,000,000 K.   
       
   2Containing some 10^15 grams of matter, coronal mass ejections aren't as   
   massive as they sound. It would take a hundred of the June 7th CMEs to make a   
   decent-sized comet; e.g., the nucleus of Halley's Comet masses about 2 x 10^17   
   gm. "Remember that this is just a magnetized cloud of gas leaving from the   
   quite tenuous corona," notes Vourlidas. "The cloud is big, but really not very   
   massive compared to things like comets, moons, and planets."   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.62   
    * Origin: NCS BBS (1:3828/7)