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Huge explosion traced to exotic star

Astronomers pinpoint source of unprecedented radiation surge.

A cataclysmic 'starquake' is thought to have caused a flare of radiation that ripped past the Earth on 27 December, battering instruments on satellites and lighting up our atmosphere.

Scientists say this is the biggest blast of gamma and X-rays they have ever observed in our corner of the Universe. They believe the flare came from a bizarre object just 20 kilometres wide on the other side of the Galaxy.

"This is a once-in-a-lifetime event," says Rob Fender of Southampton University, UK, one of the researchers studying data on the flare. "The object released more energy in a tenth of a second than the Sun emits in 100,000 years."

Astronomically speaking, this was in our backyard. Bryan Gaensler , Harvard-Smithsonian Center for Astrophysics

Data from satellites and ground-based telescopes have pinpointed the origin of the burst as SGR 1806-20, a 'magnetar' around 50,000 light-years away in the constellation of Sagittarius. Magnetars are extremely dense, small stars with magnetic fields at least a thousand trillion times stronger than the Earth's. They are a type of neutron star, the compact remnant of a collapsed sun.

The flare may have been caused by a quake on the surface of SGR 1806-20, suggest researchers. The quake would have disturbed the star's magnetic field, creating an explosion that was the brightest ever detected beyond our Solar System.

Swift answers

It is possible that similar flares have been misinterpreted in the past. Analogous gamma ray bursts have been detected, but they were assumed to come from very distant objects beyond our galaxy.

A satellite launched last November is ideally positioned to resolve the issue. NASA's Swift Gamma Ray Burst Mission is designed to locate and measure bursts. "Answers to these questions could come any day now that Swift is in orbit," says Neil Gehrels of NASA's Goddard Space Flight Center in Maryland.

Safe distance

Fortunately for life on Earth, the nearest known magnetar is about 13,000 light years away - too far for any future burst to damage the planet. The radiation burst from a closer explosion could, for example, wipe out the ozone layer.

"Astronomically speaking, this was in our backyard," says Bryan Gaensler of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and an author of a paper about the burst that has been accepted for publication in Nature. "If it were in our living room, we'd be in big trouble."

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Harvard-Smithsonian Center for Astrophysics

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Giles, J. Huge explosion traced to exotic star. Nature (2005). https://doi.org/10.1038/news050214-18

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