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How does small star let off a huge explosion?

A tiny star recently unleashed what is considered the brightest burst of light ever seen in the universe from a normal star, astronomers announced today.
Image: Artist interpretation of red dwarf star
In this artist's conception, an incredibly powerful flare erupts from the red dwarf star EV Lacertae.Casey Reed / NASA
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A tiny star recently unleashed what is considered the brightest burst of light ever seen in the universe from a normal star, astronomers announced today.

Shining with only 1 percent of the sun's light and boasting just a third of the sun's mass, this run-of-the-mill star previously was nothing to write home about. On April 25, the red dwarf star, known as EV Lacertae, unleashed a mega-flare, packing the power of thousands of solar flares. Since the star is located 16 light-years away, in reality, the flare actually occurred 16 years ago.

The flare was first seen by the Russian-built Konus instrument on NASA's Wind satellite in the early morning hours of April 25. Two minutes later, Swift's X-ray Telescope caught the flare. The star remained bright in X-rays for eight hours before settling back to normal.

It would have been visible to the naked eye if the star had been easily observable in the night sky at the time. EV Lacertae's constellation, Lacerta, is visible in the spring for only a few hours each night in the Northern Hemisphere.

"Here's a small, cool star that shot off a monster flare," said lead researcher Rachel Osten, a Hubble Fellow at the University of Maryland, College Park and NASA's Goddard Space Flight Center in Greenbelt, Md. "Flares like this would deplete the atmospheres of life-bearing planets, sterilizing their surfaces."

The star, with an estimated age of a few hundred million years, has a history of flares, though none as bright as the most recent one.

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Osten says giant flares like this one are analogous to solar flares, but stellar flares are hundreds and sometimes thousands of times more powerful. The extra power likely comes from the stars' magnetic fields. For instance, EV Lacertae rotates once every four days, much faster than the sun's four-week rotation. The star's quick rotation generates strong localized magnetic fields, about 100 times as powerful as the sun's.

"These flares are ultimately related to the twisting and tangling of magnetic fields that are poking out of the surface of the star, and stars like it," Osten told

And like the sun, EV Lacertae is covered in spots, which move around during outbursts.

"If we could look at the surface of the star as it was undergoing this flare, we would probably see that the spots on the surface rearrange themselves," Osten said. "The spots on the star cover a much larger fraction of the surface than they do on the sun, so the resulting change of the spots would be even more dramatic."

Since EV Lacertae is 15 times younger than the sun, it provides a window into our solar system's early history, scientists say. Younger stars rotate faster and generate more powerful flares. So in its first billion years, the sun must have let loose millions of energetic flares that would have profoundly affected Earth and the other planets.