The most powerful solar flare on record lasted 20 hours and accelerated solar particles to two-thirds the speed of light. (Photo: NASA)

The sun may seem bright through your own eyes, but it was at its brightest when viewed through NASA's Fermi Gamma-ray Space Telescope a few months ago. During a powerful solar blast on March 7, the solar observatory recorded the highest-energy light ever associated with an eruption from the sun.

The solar flare - a burst of light and charged particles - produced such a wealth of gamma rays that the sun briefly became the brightest object in the gamma-ray sky.

"For most of Fermi's four years in orbit, its LAT saw the sun as a faint, steady gamma-ray source thanks to the impacts of high-speed particles called cosmic rays," said Nicola Omodei, an astrophysicist at Stanford University in California. "Now we're beginning to see what the sun itself can do."

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The gamma rays emitted - which have higher energies than X-rays - were 2 billion times more energetic than visible light, which makes this observation a record-setting detection during or immediately after any previously seen solar flare.

"The sun is [usually] not a very bright source in gamma rays," said Omodei, according to Space.com. "We don't detect the sun on a daily basis. On the other hand, on March 7, the sky looked completely different, as the sun became an intense, bright source of high-energy gamma rays."

That intensity lasted for about 20 hours, which is two-and-a-half times longer than any solar flare on record.

So what exactly was happening for 20 hours to produce such a flare? Eruptions on the sun are the result of accelerated charged particles which collide with matter in the sun's atmosphere and on its surface. When protons - positively charged subatomic particles - interact, they produce pions, which decay and result in high-energy gamma rays. When the heart of an atom, a nucleus, is excited by collisions, it gives off gamma rays as it settles down. And accelerated electrons - negatively charged subatomic particles - also give off gamma rays as they collide with protons and atomic nuclei.

Fermi's Large Area Telescope scans the entire sky every three hours looking for gamma rays, and this event was also recorded by the Gamma-ray Burst Monitor (GBM).

"Seeing the rise and fall of this brief flare in both instruments allowed us to determine that some of these particles were accelerated to two-thirds of the speed of light in as little as 3 seconds," said Michael Briggs, a member of GBM team at the University of Alabama in Huntsville.