For a fraction of a second in December, a dying remnant of an exploded star let out a burst of light that outshone the Milky Way's other half-trillion stars combined, astronomers announced Friday.
Even on Earth, half a galaxy away, the starburst was one of the brightest objects ever observed in the sky, after the sun and perhaps a few comets.
"Whoppingly bright," said Dr. Bryan M. Gaensler, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. "It gave off more energy in 0.2 seconds than the sun does in 100,000 to 200,000 years."
No one on Earth directly saw the flare because most of the light was gamma rays, photons that are more energetic than X-rays and are blocked by the atmosphere. But the Dec. 27 pulse registered on instruments aboard 15 spacecraft, including NASA's new Swift satellite, which was designed to record cosmic gamma rays and had been turned on just the week before.
The radiation even temporarily compressed Earth's ionosphere, an envelope of charged gas at the top of the atmosphere, and distorted long-wavelength radio signals.
"It was really the big one," said Dr. Kevin Hurley, a researcher at the Space Sciences Laboratory at the University of California, Berkeley.
Hurley and others pinpointed the origin of the pulse as a neutron star known as SGR 1806-20, about 50,000 light-years away in the constellation Sagittarius. Neutron stars are remnants of stars after they have exploded in supernovas.