Pipsqueak Star Unleashes Monster Flare

illustration credit: Casey Reed/NASA - An artist's illustration of EV Lacertae, which produced the brightest flare ever seen from a normal star other than our Sun on 25 April 2008.

The brightest flare ever seen from a normal star other than our Sun has been detected by satellites including NASA's Swift observatory, which is controlled from Penn State University's Mission Operations Center at University Park. The explosive release of energy packed the power of thousands of solar flares combined. The flare was so bright it would have been visible to the naked eye if the star had been easily observable in the night sky at the time.

The star that produced the flare is one of the closest stars outside Earth's solar system, located at a distance of only 16 light-years. Named EV Lacertae, it is a red-dwarf star that shines with only one percent of the Sun's light, contains only a third of the Sun's mass, and has a faint glow (magnitude-10) that is far below the range for visibility by the naked eye. "I find it remarkable that the Swift satellite, which is designed to detect the explosive birth of black holes in distant galaxies, can also detect explosions on stars in the immediate neighborhood of our Sun," said Eric Feigelson, a member of the observation team and a professor of astronomy and astrophysics at Penn State.

EV Lacertae's constellation, Lacerta, is visible in the spring for only a few hours each night in the Northern Hemisphere. But 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 was first seen by the Russian-built Konus instrument on NASA's Wind satellite in the early morning hours of April 25. Swift's X-ray Telescope caught the flare less than two minutes later, and quickly rotated to point directly toward EV Lacertae. 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 8 hours before settling back to normal.

"Here's a small, cool star that shot off a monster flare," says Rachel Osten, a Hubble Fellow at the University of Maryland and at NASA's Goddard Space Flight Center in Greenbelt, Maryland. EV Lacertae, a red dwarf, is the most common type of star in the universe. "Flares like this would deplete the atmospheres of life-bearing planets, sterilizing their surfaces," Osten said.

EV Lacertae can be likened to an unruly child that throws frequent temper tantrums. The star is relatively young, with an estimated age of a few hundred million years. 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 local magnetic fields, making it more than 100 times as magnetically powerful as the Sun's field. The energy stored in its magnetic field powers these giant flares.

The flare's incredible brightness enabled Swift to make detailed measurements, providing scientists with a golden opportunity to study a stellar flare on a second-by-second basis to see how it evolved. Since EV Lacertae is 15 times younger than our Sun, it provides a window into our own 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," a spokesperson at NASA's Goddard Space Flight Center explained.

Flares release energy across the electromagnetic spectrum, but the extremely high gas temperatures produced by flares can be studied only with high-energy telescopes like those on Swift. Swift's wide field of view and rapid repointing capabilities, designed to study gamma-ray bursts, make it ideal for studying stellar flares. Most other X-ray observatories have studied this star and others like it but, due to their much smaller fields of view, they would have to be extremely lucky to catch and study such flares.

CONTACTS

Eric Feigelson: (+1)814-865-0162, efeigelson@astro.psu.edu

Barbara Kennedy (PIO): (+1) 814-863-4682, science@psu.edu