12 July 2011

Ballistic plasma blast results in solar tsunami

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A flash of X-rays have been detected coming from the western edge of the solar disk. The blast at first appeared to be a run-of-the-mill eruption, until researchers looked at the movies.
solar blast

Still from one of the Solar Dynamics Observatory videos shows a close-up of the June 7 eruption with dark blobs of plasma falling ballistically toward the surface of the Sun. Click through to see what happens next. Credit: NASA

solar blast

Plasma blobs are funneled toward sunspots by magnetic fields. Credit: NASA

MARYLAND: A flash of X-rays have been detected coming from the western edge of the solar disk. The blast at first appeared to be a run-of-the-mill eruption, until researchers looked at the movies.

“We’d never seen anything like it,” said Alex Young, a solar physicist at the Goddard Space Flight Centre in Maryland, of the videos recorded by the Solar Dynamics Observatory (SDO) on 7 June 2011. “Half of the Sun appeared to be blowing itself to bits.”

“In terms of raw power, this really was just a medium-sized eruption,” said Young, “but it had a uniquely dramatic appearance caused by all the inky-dark material. We don’t usually see that.”

Like guided missiles

Solar physicist Angelos Vourlidas of the Naval Research Lab in Washington DC called it a case of “dark fireworks.”

“The blast was triggered by an unstable magnetic filament near the Sun’s surface,” he said. “That filament was loaded down with coo1 plasma, which exploded in a spray of dark blobs and streamers.”

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,” said Young.

Shadowy shock wave detected

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.

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 one after another with a domino sequence of flares going off all around the star.

“The June 7 blast didn’t seem to trigger any big secondary explosions, but it was certainly felt far and wide,” said Young.

Downright common?

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 approximately two greater than the June 7 cloud. The amount of material that fell back to the Sun on June 7 was approximately equal to the amount that flew away, Vourlidas said.

As remarkable as the June 7 eruption seems to be, Young said it might not be so rare. “In fact,” he said, “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-centre snapshot at the beginning or end of the blast to hint at what actually happened.

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