Dance of the dead

11:48am, March 13, 2007
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The neutron star XTE J1739-285 is the burned-out remains of what was once a brilliant celestial body. Now, astronomers have evidence that it's the fastest-spinning stellar corpse known.

X-ray observations indicate that the neutron star spins 1,122 times a second, about 30 percent faster than the previous record holder, report Phil Kaaret of the University of Iowa in Iowa City and his colleagues in the March 10 Astrophysical Journal Letters.

NASA's Rossi X-ray Timing Explorer discovered the neutron star in 1999 when it emitted bursts of X rays. After several years of quiescence, it began sending out new bursts in 2005. Studies of other neutron stars had shown that variations in the brightness of X-ray bursts indicate the stars' rotation rates.

Late last year, the Rossi telescope found oscillations indicating that XTE J1739-285 was spinning faster than any neutron star previously observed. Since then, the star has again quieted, and scientists are waiting to observe more bursts to confirm the high spin rate, Kaaret and his team say.

The maximum rotation of a neutron star would reveal its composition, notes Kaaret. For instance, an interior composed solely of electrons and protons squeezed together into neutrons can't be compressed as much as more-exotic particles can and so can't rotate as rapidly. Additional studies of the spin rates of neutron stars might let astronomers rule out some estimates of the objects' compositions.

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