A massive burst of energy exploded from a far-off neutron star (search) last December, the brightest flash of light ever detected from beyond the solar system, scientists said Friday.

The Dec. 27 flare was by far the largest of three such giant outbursts of gamma rays (search) detected in the last 35 years from neutron stars, the densely packed and supercharged remnants of a collapsed star.

"This is a once-in-a-lifetime event," David Palmer, a scientist at the Los Alamos National Laboratory in New Mexico and lead author of a paper on the flare.

The energy burst, packing more energy than the sun emits every 150,000 years, was not visible to humans, and the gamma rays were blocked by the Earth's atmosphere as they rushed by. Scientists said some operators of low-frequency transmitters were able to detect it.

NASA's (search) new observatory — named Swift for its speedy pivoting and pointing — is among the instruments that detected the flare. It was launched last November to probe the workings of black holes. The satellite, controlled by scientists at the Goddard Space Flight Center in Greenbelt, is designed to detect gamma ray outbursts and quickly pivot to record them. It also recorded the afterglow of the blast.

"Swift, within a mere month of its launch, was able to participate in an amazing discovery," said Roger Blandford, a physicist at Stanford University.

Neutron stars are formed when massive stars run out of fuel and collapse, creating dense, fast-spinning and highly magnetic solar corpses that are only about 15 miles in diameter.

The December burst lasted a tenth of second and came from a neutron star about 50,000 light years away from Earth in the constellation Sagittarius. Called SGR 1806-20, it is one of only about 12 known magnetars, a neutron star with a magnetic field that is trillions of times stronger than that of Earth.

Scientists believe the magnetic field of the magnetars can shift like an earthquake, causing it to eject a huge burst of energy. SGR 1806-20 is know as a "soft gamma repeater" because the initial flare is followed by a series of much smaller releases of gamma rays. The December flare was up to a billion times more powerful than typical flares from soft gamma repeaters.

The aftermath of the blast is a smoldering oblong ring that glows for several days after the flare caused by debris launched into the gas surrounding the star.