NASA - National Aeronautics and Space Administration

An artist depicts the incredibly powerful flare that erupted from the red dwarf star EV Lacertae. Credit: Casey Reed/NASA
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> Print resolution For many years scientists have known that our Sun gives off powerful explosions known as flares. These flares contain millions of times more energy than atomic bombs, so they are very powerful by human standards.

But when astronomers compare flares from the sun to flares on other stars, the sun’s flares lose. On April 25, NASA’s Swift satellite picked up a record-setting flare from a star known as EV Lacertae. This flare was thousands of times more powerful than the greatest observed solar flare. But because EV Lacertae is much farther from Earth than the sun, the flare did not appear as bright as a solar flare. Still, it was the brightest flare ever seen from a star other than the sun.

What makes the flare particularly interesting is the star. EV Lacertae is much smaller and dimmer than our Sun. In other words, a tiny, wimpy star is capable of packing a very powerful punch.

How can such a small star produce such a powerful flare? The answer can be found in EV Lacertae’s youth. Whereas our Sun is a middle-aged star, EV Lacertae is a toddler. The star is much younger than the Sun, and is still spinning rapidly. The fast spin, together with its churning interior, whips up gases to produce a magnetic field that is much more powerful than the sun’s magnetic field. The energy of this field can produce giant flares like the one Swift saw on April 25.

This giant flare would be bad news for any planets orbiting the star. "Flares like this would deplete the atmospheres of life-bearing planets, sterilizing their surfaces," says Rachel Osten, of the University of Maryland, College Park and NASA’s Goddard Space Flight Center in Greenbelt, Md. Osten is leading the scientific analysis of the flare.

Scientists are very excited about this flare because it is easy to study. The flare’s incredible brightness enabled Swift to make detailed measurements. "This gives us a golden opportunity to study a stellar flare on a second-by-second basis to see how it changed," says Stephen Drake of NASA Goddard.

Since EV Lacertae is much younger than our Sun, it gives us a window into our solar system’s early history. 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 bombarded Earth and the other planets, making it difficult for life to arise and flourish.

Robert Naeye
Goddard Space Flight Center