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December 24: Flare and Eruption

  December 24: Flare and Eruption  
  2011-Jun-07 M Flare and Amazing Eruption  


Click on the above image for a link to a movie showing the flare and eruption



Perhaps the single most dramatic events ever observed by PROBA2 was the prominence eruption and associated M-class flare on June 7, 2011. Although the flare was only a moderate one, it must have been driven by an explosive event low in the solar atmosphere to throw off such a massive cloud of cool, dense material. While this sort of eruption of cool prominence material is relatively common, it is extremely rare for the promeince material to spread into such a huge cloud and rarer still for it to rain back down to the solar surface in such dramatic fasion.

The eruption unfolded in several stages. First, a huge explosion kicks off a shock wave that races out into the corona in all directions. You can see this shock early in the movie, first as a faint dome-shaped feature near the site of the eruption, then, as an expanding dimming of the corona as the shock from the eruption blows away much of the coronal material near the site of the eruption's onset. Then a huge cloud of cool, dense material forms. (We know that this material is cool because SWAP sees it as dark, meaning it is not is SWAP's near the 1 million degree temperature range to which swap is sensitive. We know it is dense because it obscures the structures behind it; there's so much material that the light from the bright corona behind cannot penetrate it.) Finally the cloud of material is blasted up into space and falls back again under the influence of the sun's gravity. As each little blob of material falls to the sun's surface, it is heated by interaction with the surrounding corona, giving off a dramatic flash of light as it dissipates back into the sun's atmosphere. And here's something worth noting: each little blob of dark material we see, that's a blob of sun-stuff, temperature tens of thousands of degrees, about the size of planet Earth. This eruption dwarfs anything you could ever imagine!

Also worth noting, the flows and blobs don't simply fall back towards the sun along the parabolic trajectories that might be expected if the downflowing material was moving only under the influence of gravity, they appear to travel on predetermined tracks, sliding like beads on an invisible wire. This is due to the erupting plasma's interaction with the Sun's invisible magnetic fields. Once trapped on a magnetic field line the plasma can only flow along the field, not across it, causing it to follow the fields back to the surface. Some of the material even appears to change direction as it moves back to the solar surface: this is due to the complex interaction of different magnetic fields and magnetic flux tubes.

The above image may look strange but it has been reprocessed to straighten out the solar disk creatng one flat surface. An alternative, and more familiar perspective of the erruption can be seen here.


Happy Holidays from the PROBA2 team!