Monster star blast 'brighter than full Moon'
Embargoed until 0600 AEDT 19 February 2005 (1900 GMT 18 February)
Radio telescopes of CSIRO and the University of Sydney, and others in Europe, India and the USA, have been watching the aftermath of one of the most stupendous cosmic explosions ever recorded.
On 27 December last year a star 50 000 light-years away produced a monster blast of radiation that made it, for a tenth of a second, brighter than the full moon — the brightest object ever seen outside the solar system — and briefly disrupted a layer of the Earth’s atmosphere.
The event was detected by X-ray and gamma-ray instruments on NASA and European satellites, and by telescopes around the world.
The observations were presented at a NASA press briefing in Washington today. Papers on the event will appear in the journal Nature.
This ‘giant flare’ came from a highly magnetised neutron star, or magnetar, called SGR 1806-20. It may have resulted from an eruption on the star’s surface, like a solar flare from the Sun, or from a quake in the solid surface of the neutron star. Either way, it unleashed 10exp40 watts, putting out more energy in a tenth of a second than the Sun emits in 100 000 years.
“Essentially, this was a mini gamma-ray burst in our backyard,” said Dr. Bryan Gaensler of the Harvard-Smithsonian Center for Astrophysics, who led the radio observations. “It may be a once per century or once per millennium event in our Galaxy.”
“Had this happened within 10 light-years of us, it would have severely damaged our atmosphere and possibly have triggered a mass extinction. Fortunately there are no magnetars anywhere near us,” he says.
The nearest known magnetar, 1E 2259+586, is about 13 000 light-years away.
CSIRO’s Australia Telescope Compact Array started observing SGR 1806-20 on 5 January; the University of Sydney’s Molonglo Observatory Synthesis Telescope (MOST) began on 6 January.
From the characteristics of the radio emission astronomers have been able to confirm how much energy the explosion released, the physical processes involved and the geometry of the event.
“The Compact Array is a uniquely versatile and flexible instrument,” says Gaensler. “It was able to observe at frequencies other telescopes couldn’t, which allowed us to fill in the full radio ‘rainbow’.”
The first week of observing at the Compact Array was done by Katherine Newton-McGee, a University of Sydney astrophysics PhD student.
“It was very exciting—this was a hundred times larger than any such burst ever seen before,” she says.
Katherine is studying cosmic magnetic fields for her PhD, “so the magnetar was relevant”.
Other observing at the Compact Array was done by Yosi Gelfand, a PhD student at the Harvard-Smithsonian Center for Astrophysics, and staff of CSIRO’s Australia Telescope National Facility.
“The MOST got the best low-frequency observations,” says the University of Sydney’s Professor Dick Hunstead. “They confirmed that the radio source must have expanded very rapidly early on.”
SGR 1806-20 is three thousand million times further away than the Sun. “That it can reach out and tap us on the shoulder like this, reminds us that we really are linked to the cosmos,” says Dr. Phil Wilkinson of IPS Australia, which monitors ‘space weather’ and its effects on the Earth’s atmosphere.
Bryan Gaensler, Harvard-Smithsonian Center for Astrophysics
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Dr Bob Sault, CSIRO Australia Telescope National Facility
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Dr Simon Johnston, CSIRO Australia Telescope National Facility
Dr Dick Hunstead, University of Sydney
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Dr Phil Wilkinson, IPS Australia
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Katherine Newton-McGee, University of Sydney
Dr Brian Schmidt, Research School of Astronomy and Astrophysics, ANU (for independent comment)
Dr Andrew Melatos, University of Melbourne (for independent comment)
Helen Sim, CSIRO Australia Telescope National Facility