The tiny star with a monster roar
BY DR EMILY BALDWIN
ASTRONOMY NOW
Posted: May 20, 2008

The brightest flare ever seen from a normal star other than our Sun, worth thousands of solar flares, has been released from a star that shines with just one percent of the Sun’s light.

EV Lacertae is a fairly normal red dwarf, the most common type of star in the Universe, and is one of our closest stellar neighbours at a distance of just 16 light-years. But weighing in at less than one-third the mass of the Sun and offering a faint magnitude 10 glow, it is far below naked eye visibility. That is, until it released a monster flare, detected on April 25 by the Russian-built Konus instrument on NASA’s Wind satellite and followed up by the Swift satellite, that would have been easily visible with the naked eye if the star had been observable in the night sky at the time. The flare remained bright in X-rays for eight hours before settling back to normal and was so blinding it caused instruments onboard Swift to automatically shut down.

An artist impression of the incredibly powerful flare that erupted from the red dwarf star EV Lacertae last month. Image: Casey Reed/NASA.

"This gives us a golden opportunity to study a stellar flare on a second-by-second basis to see how it evolved," says Stephen Drake of NASA Goddard.

EV Lacertae rotates once every four days, generating strong localised magnetic fields that make it over one hundred times as magnetically powerful as the Sun’s field. The energy stored in its magnetic field powers the giant flares. The star is also a youthful few hundred million years old, around 15 times younger than our Sun. Younger stars rotate faster and generate more powerful flares, so in its first billion years our own Sun must have let loose millions of energetic flares that would have profoundly affected Earth and the other planets.

"Flares like this would deplete the atmospheres of life-bearing planets, sterilising their surfaces," says Rachel Osten, a Hubble Fellow at the University of Maryland and NASA Goddard.

Because of EV Lacertae’s relative youth, studying this recent eruption will give scientists a window into our Solar System’s early history.

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