Jan. 20, 2004

GW/NASA Discover New Form of Magnetar

By Matthew Lindsay

Columbian College of Arts and Sciences professors Alaa Ibrahim and William Parke, along with NASA Goddard researchers Craig Markwardt and Jean Swank, announced the discovery of the first transient magnetar, a neutron star previously too faint to be detected that recently increased dramatically in brightness. The finding, made in July 2003 with NASA’s Rossi X-ray Timing Explorer and announced at the American Astronomical Society Meeting, may ultimately fill in important gaps in neutron star evolution and magnetar identification.

The newly discovered star, dim just a year ago, is named XTE J1810-197.

“The discovery of this source came courtesy of another magnetar that we were monitoring named SGR 1806-20,” said Ibrahim, assistant professorial lecturer in physics, who last year proved the existence of magnetars when he discovered the most powerful large-scale magnetic field known to exist.

While studying SGR 1806-20, the magnetar that he confirmed, Ibrahim and his colleagues detected XTE J1810-197 about a degree to the northeast, within the Milky Way galaxy about 15,000 light years away [one light year is approximately six trillion miles].

A neutron star is the core remains of a star at least eight times more massive than the sun that exploded in a supernova event. Neutron stars are highly compact, highly magnetic, fast-spinning objects with about a sun’s worth of mass compressed into a sphere roughly 10 miles in diameter.

A magnetar is a type of neutron star, but up to a thousand times more magnetic than the average neutron star. At a hundred trillion (10^14) Gauss, magnetars have the most powerful large-scale magnetic fields yet detected in the universe and are so magnetic that they could strip a credit card clean at a distance of 100,000 miles. The Earth’s magnetic field, in comparison, is about 0.5 Gauss, and a strong refrigerator magnet is about 100 Gauss. Magnetars are brighter in X-rays than they are in visible light, and they are the only stars known that shine predominantly by magnetic power. Studying magnetars will allow researchers to test the predictions of theoreticians and their proposed laws of nature, specifically the interaction between light and matter, in some of the universe’s most exotic conditions.

While only nine magnetars currently have been identified for certain, scientists estimate at least 100 may be present in the Milky Way galaxy. The team’s research and findings explain the discrepancy between the small number of identified magnetars and the estimated number of magnetars in our galaxy.

“The discovery of a transient magnetar is a strong indication that many magnetars spend a significant portion of their lives undetected in a relatively inactive state,” said Parke, professor of physics.

The transient behavior of XTE J1810-197 also provides important insight toward a greater understanding of the evolution of several classes of neutron stars. Discussion of a connection among magnetars and two other neutron star families has surfaced in the scientific community in recent years.

“XTE J1810-197’s evolution provides the first tangible evidence in favor of such a kinship,” said Ibrahim. “With a few more examples of stars showing a similar trend, a magnetar family tree may be emerging.”

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