Scientists detected a flash of light from across the Galaxy so powerful; it bounced off the moon and lit up the Earth’s upper atmosphere. The flash was brighter than anything ever detected from beyond our Solar System, and it lasted over a tenth of a second.<\/p>\n
NASA and European satellites and many radio telescopes detected the flash and its aftermath on December 27, 2004. <\/p>\n
NASA’s Swift satellite and the National Science Foundation-funded Very Large Array (VLA) were two of many observatories that observed the event arising from neutron star SGR 1806-20. It is a unique neutron star called a magnetar, about 50,000 light years from Earth in the constellation Sagittarius.
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\nThe apparent magnitude was brighter than a full moon and all historical star explosions. The light was brightest in the gamma-ray energy range, far more energetic than visible light or X-rays and invisible to our eyes.<\/p>\n
“This might be an once-in-a-lifetime event for astronomers, as well as for the neutron star,” said Dr. David Palmer of Los Alamos National Laboratory, N.M. He is lead author on a paper describing the Swift observation. “We know of only two other giant flares in the past 35 years, and the December event was 100 times more powerful,” he added.<\/p>\n
Dr. Bryan Gaensler of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., is lead author on a report describing the VLA observation, which tracked the ejected material as it flew out into interstellar space.<\/p>\n
Other key scientific teams are associated with radio telescopes in Australia, The Netherlands, United Kingdom, India and the United States, as well as with NASA’s High Energy Solar Spectroscopic Imager (RHESSI).<\/p>\n
Neutron stars form from collapsed stars. They are dense, fast-spinning, highly magnetic, and only about 15 miles in diameter. Only about 12 magnetars are known among the millions of regular neutron stars in our Galaxy and neighboring galaxies.<\/p>\n
SGR 1806-20 is also a soft gamma repeater (SGR) because it randomly flares and releases gamma rays. Only four SGRs are known. The giant flare on SGR 1806-20 was millions to billions of times more powerful than typical SGR flares. For a tenth of a second, the giant flare unleashed more energy than the sun emits in 150,000 years. Magnetic fields around magnetars are responsible for SGR outbursts, but the details remain unclear.<\/p>\n
“The next biggest flare ever seen from any soft gamma repeater was peanuts compared to this incredible December 27 event,” Gaensler said. “Had this happened within 10 light years of us, it would have severely damaged our atmosphere. Fortunately, all the magnetars we know of are much farther away than this,” he added.<\/p>\n
During the 1980s scientists wondered whether gamma-ray bursts were star explosions from beyond our Galaxy or eruptions on nearby neutron stars. By the late 1990s it became clear gamma-ray bursts did indeed originate far away. But the extraordinary giant flare on SGR 1806-20 reopens the debate, according to Dr. Chryssa Kouveliotou of NASA’s Marshall Space Flight Center, Huntsville, Ala., who coordinated multiwavelength follow-up observations. A small percentage of short gamma-ray bursts, less than two seconds, could be from SGR flares.<\/p>\n
“An answer to the short gamma-ray burst mystery could come any day now that Swift is in orbit”, said Swift lead scientist Neil Gehrels.<\/p>\n
Scientists around the world have been following the December 27 event. RHESSI detected gamma rays and X-rays from the flare. Drs. Kevin Hurley and Steven Boggs of the University of California, Berkeley, are leading the effort to analyze these data.<\/p>\n