Astronomers have observed an explosion on a nearby star equal to 50 million trillion atomic bombs. The flare was so powerful that if it had happened on our own sun it would have wiped out life on Earth in a mass extinction.

It happened on a star called 11 Pegasi which lies about 135 light-years away, on our doorstep in cosmic terms. It is in orbit around another star.

The monster flare, which was spotted by Nasa’s Swift satellite, is believed to be the most powerful magnetic explosion detected on a star. The observation was reported on Tuesday at a conference in Pasadena, California, but was made last December.

Nasa say the flare was about 100 million times more energetic than a typical flare on our own sun, such as that in our Nasa photo, which is too stable to produce anything so powerful. They add that 11 Pegasi, which is slightly less massive than the sun, is at a safe distance and so does not threaten life on Earth.

Scientists say the obsrvation has shown that flares on other stars involve particle acceleration just like on the sun. Solar flares originate in the sun’s corona, the outermost part of the sun’s atmosphere, as a burst of radiation.