Giant ring found circling monster magnetar
BY DR EMILY BALDWIN
ASTRONOMY NOW
Posted: May 29, 2008

NASA’s Spitzer Space Telescope has found a bizarre ring of material around a rare and exotic stellar corpse, displaying a magnetic field trillions of times more intense than the Earth’s.

The stellar corpse belongs to a class of objects known as magnetars, the cores of massive stars that blew up in supernova explosions, but unlike other dead stars, they slowly pulsate with X-rays and have extremely strong magnetic fields of around 1,000,000,000,000,000 gauss, while in comparison, Earth's magnetic field strength registers at 0.5 gauss, the Sun at one gauss and a sunspot at about 1,000 gauss. These extreme fields stretch the very fabric of matter, contorting atoms into thin cigar-shaped structures.

Out of the 400 billion stars in our Galaxy, there are about a dozen known magnetars. The discovery of a ring around magnetar SGR 1900+14 is particularly special because it identifies a new phenomenon associated such objects. "It's the first time something like this has ever been seen around a magnetar," says Vikram Dwarkadas of the University of Chicago.

The image shows a ghostly ring extending seven light years across the corpse of a magnetron star, located in the centre of the image. The very bright region near the centre is a cluster of young stars, which may be illuminating the inner edge of the bubble, making it look like a ring in projection. Image: NASA/JPL-Caltech.

The scientists working on the data believe that the ring formed when the magnetar erupted in a giant flare that excavated a nearby cloud of dust, leaving an outer dusty ring. It could not have formed during the original supernova explosion as any material as close to the star as the ring would have been disrupted by the supernova shock wave. Scientists suspect that the ring my actually be the edges of a bubble that was hollowed out by an explosive burst from the magnetar in 1998.

"It's as if the magnetar became a huge flaming torch and obliterated the dust around it, creating a massive cavity,” says Chryssa Kouveliotou of NASA's Marshall Space Flight Centre. "Then the stars nearby lit up a ring of fire around the dead star, marking it for eternity."

The discovery could help scientists determine if a star's mass influences whether it becomes a magnetar when it dies. Though scientists know that stars above a certain mass will "go supernova," they do not know if mass plays a role in determining whether the star becomes a magnetar or a run-of-the-mill dead star. By studying the masses of stars located nearby, it might be possible to estimate the approximate mass of the original star that exploded and became SGR 1900+14. The nearby stars could also explain why the ring is only glowing at certain infrared wavelengths that Spitzer can see, and not spewing out X-ray and radio waves common to other supernova remnants.

"The nearby massive stars are most likely what's heating the dust and lighting it up,” says Enrico Ramirez-Ruiz of the University of California. “This means that the magnetar, which lies at the exact centre of the ring, is associated with the massive star-forming region."

The magnetar is evidently still alive in many ways, interacting with its environment and making a big impact on the young star-forming region where it was born. The results of the discovery are presented in this week's issue of Nature.

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