ON 27 December, a blast of gamma rays that lasted a mere quarter of a second overwhelmed detectors on many satellites orbiting Earth. Researchers have now traced the burst to a neutron star within our galaxy, and this discovery could be a clue to the origin of other gamma-ray bursts that have so far defied explanation.
The blast 鈥渨as so bright, it came right through the body of the Swift satellite, even though Swift wasn鈥檛 pointed at the object鈥�, says John Nousek of Pennsylvania State University in University Park. Nousek is mission director for Swift, a NASA satellite that detects gamma-ray bursts.
The outburst was followed by a fainter afterglow of gamma rays lasting for about 8 minutes, which showed a recurring signal every 7.5 seconds. This allowed scientists using the European Space Agency鈥檚 Integral spacecraft to trace the source of the 鈥渟uperflare鈥� to a neutron star called SGR 1806-20, which is known to spin at that rate and lies about 30,000 to 50,000 light years away in the constellation Sagittarius. SGR 1806-20 is an example of a rare kind of star called a magnetar 鈥� a neutron star with a magnetic field so strong it could wipe a credit card鈥檚 data from a distance of 160,000 kilometres.
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The magnetar is one of the Milky Way鈥檚 three known 鈥渟oft gamma repeaters鈥� (SGRs), which sporadically release low-energy gamma rays. SGRs have emitted energetic bursts at least twice before, but nothing to match the latest display. The energy in the initial burst of the most recent flare was 100 times that of the previous superflares.
But this did not surprise astrophysicists. 鈥淚 wasn鈥檛 shocked at the energy it was putting out,鈥� says Christopher Thompson of the Canadian Institute for Theoretical Physics, who worked on the most widely accepted magnetar model. 鈥淭he total energy implied by the models is enough to power a dozen or more of these events in the life of one magnetar.鈥�
鈥淭he blast was so bright it came right through the body of the satellite, even though it wasn鈥檛 pointed at the source鈥�
Superflares may occur when some of the magnetar鈥檚 magnetic fields rip loose, unleashing a fireball of particles and radiation that astronomers see as a bright flash of gamma rays.
Identifying the source of this flare may have solved one of astronomy鈥檚 biggest mysteries. If it had occurred more than 100 million light years away, the flare would have looked indistinguishable from a short gamma-ray burst 鈥� a cosmic phenomenon that has baffled astronomers for years. 鈥淚鈥檓 fairly confident that SGRs account for at least some short gamma-ray bursts,鈥� says David Palmer, a Swift team member at Los Alamos National Laboratory in New Mexico.
