WASHINGTON -- Astronomers using the Hubble Space Telescope spotted a brief flash of ultraviolet light just before a massive explosion on a puny star, a discovery that may help explain the cause of solar flares.
When a flare occurs on the sun, it can block radio communications, disrupt power supplies and threaten the health of astronauts. Some scientists think that the long-term cycles of solar flares may alter Earth's climate.
Bruce E. Woodgate, an astronomer with the Goddard Space Flight Center, said yesterday that one of the Hubble's light-analyzing spectrographs was pointed at a star called AU Microscopium last Sept. 3 when the instrument detected a three-second burst of ultraviolet light at specific wavelengths.
That kind of flash, coming just before a stellar flare, supports a theory proposed 16 years ago by Frank Orrall and Jack Zirker of the National Solar Observatory in New Mexico. But the phenomenon had never been seen in any star, including the sun.
The Orrall-Zirker theory says that the magnetic fields swirling on the surface of stars, including the sun, act like man-made particle accelerators, stripping atoms apart and sending the pieces careening along lines of magnetic force.
Flares, the theory says, are triggered when a beam of protons -- positively charged particles found in the atom's nucleus -- accelerate inside one of these magnetic field and strike the star's dense atmosphere, causing a geyser of heat and radiation.
Astronomers said the ultraviolet light from AU Microscopium was apparently produced by protons moving at about 1,100 miles per second toward the surface of the star.
Dr. Woodgate said the Hubble discovery suggests that proton beams are "the dominant energy source in the first phase of a solar flare." If so, he said, the triggering phase of a flare may pack 100 times the energy scientists previously thought.
NASA researchers pointed out that a solar flare in March 1989 knocked out the electrical grid across the province of Quebec, created an aurora borealis visible as far south as Florida and probably gave some airline passengers a dose of radiation equivalent to a chest X-ray.