Hidden power: An artist's impression depicts the incredibly powerful flare that erupted from the red dwarf star EV Lacertae.

Credit: Casey Reed/NASA

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SYDNEY: A tiny star has unleashed a solar flare so massive that it would have been visible to the naked eye in the night sky. It is the brightest flare ever observed from a star other than the Sun.

"Here's a small, cool star that shot off a monster flare. This star has a record of producing flares, but this one takes the cake," said Rachel Osten, an astronomer at the University of Maryland, in College Park, USA. "Flares like this would deplete the atmospheres of life-bearing planets, sterilizing their surfaces."

Explosive release

The flare was an explosive release of magnetic energy, packing the power of thousands of solar flares produced by our Sun and was spotted on 25 April by NASA's Swift Satellite.

When Swift tried to observe the star with its Ultraviolet/Optical Telescope, the flare was so bright that the instrument shut itself down for safety reasons. The star remained bright in X-rays for eight hours before settling back to normal.

The star, known as EV Lacertae, is one of our closest neighbours, but isn't much to write home about. It's an ordinary red dwarf – by far the most common type of star in the universe – and shines with only one per cent of the Sun's light.

The star rotates once every four days, which is much faster than the Sun, which rotates once every four weeks. EV Lacertae's fast rotation generates strong localised magnetic fields, making it more than 100 times as magnetically charged as the Sun's field. The energy stored in its magnetic field powers these giant flares.

Rapidly rotating

EV Lacertae's constellation, Lacerta, is visible in the spring for only a few hours each night in the Northern Hemisphere. But NASA says that if the star had been more easily visible, the flare probably would have been bright enough that the star could have been seen with the naked eye for one to two hours.

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 evolved," said Stephen Drake of NASA's Goddard Space Flight Centre in Maryland.

Since EV Lacertae is 15 times 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 profoundly affected Earth and the other planets.

In reference to NASA's Swift satellite, astronomer Eric Feigelson of Penn State University in University Park, U.S. said: "I find it remarkable that a satellite designed to detect the explosive birth of black holes in distant galaxies can also detect explosions on stars in the immediate neighbourhood of our Sun."