Giant eruption reveals

dead star

BY DR EMILY BALDWIN

ASTRONOMY NOW

Posted: 17 June, 2009

X-rays from an enormous stellar eruption which arrived at the Earth in August last year originated from a rare group of dead star known as a magnetar.

Magnetars are the most intensely magnetized objects in the Universe, boasting magnetic fields some 10,000 million times stronger than our planet Earth. To put that in context, if a magnetar existed half way between the Earth and the Moon, its magnetic field would wipe the details off every credit card on Earth.

Magnetars are the most intensely magnetised objects in the Universe. Image: NASA.

“Magnetars allow us to study extreme matter conditions that cannot be reproduced on Earth,” says Nanda Rea from the University of Amsterdam, who led the team that performed the research.

Fortunately magnetar SGR 0501+4516 lies 15,000 light years away, presenting no danger to us. Traveling through space for many thousands of years, its X-rays were felt by the NASA-led Swift satellite on 22 August 2008. Along with ESA’s XMM-Newton and Integral space observatories, an intense observation campaign began to record the four month long outburst, during which many smaller bursts were also detected.

Outbursts from a magnetar are thought to occur when its intense magnetic field becomes unstable and pulls the star’s crust apart, allowing matter to spew out and tangle up in the magnetic field lines. This can result in an even more unstable configuration of the magnetic field lines, releasing even more energy. Integral detected one such outburst five days after the main eruption, which persisted for 10 days and beyond the energy range that XMM-Newton can see, the first time such transient X-ray emission was detected during the outburst.

High energy X-ray emission from SGR 0501+4516 was observed by Integral. Image: Credits: ESA/INTEGRAL/IBIS-SIGRI (Rea et al. 2009).

Since magnetars are extremely rare – just 15 are known in our Galaxy – there is no conclusive evidence for how they form. There are two prevailing theories, however, one is that it is the tiny core left behind after a highly magnetic star has died; the other is that during the death of a normal star, its tiny core is accelerated, providing a dynamo that strengthens its magnetic field, turning it into a magnetar.

“If we could just find a magnetar in a cluster of highly magnetic stars, that would prove it [the first idea],” says Rea. The hunt is on, and in the case of SGR 0501+4516, the team will use XMM-Newton to observe this curious object again next year, when they hope to see it in a quiescent state so they can study the calm after the storm.

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