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Newly Discovered Pulsar Spins its Way into History

ASCA image of N157B
ASCA image of N157B
Credit: Wang & Gotthelf (ApJ, 1998, 494, 623)

Astronomers have discovered a neutron star spinning at a rate of over 60 times a second! The star, a pulsar believed to have formed in a supernova explosion some five thousand years ago, is spinning faster than most scientists believed possible for such an object. The pulsar was found by a team of astronomers including Frank Marshall, William Zhang, and Eric Gotthelf from NASA's Goddard Space Flight Center, along with John Middleditch from Los Alamos National Laboratory. "The pulsar is spinning twice as fast as any young pulsar that we have seen before," said Marshall. "To put it in perspective, this pulsar is spinning more than 6 million times as rapid as the Earth."

Astronomers compared this newly found pulsar with the pulsar in the Crab supernova remnant and found:

age5000 yrs1000 yrs
current period16 ms33 ms
spin-down rate *5.12 e-14s/s4.2269 e-13s/s

So the N157B pulsar is much older but has spun down about ten times more slowly, and thus retained much of its initial spin. This might be due to the relative magnetic field strength of the pulsars. This important new addition to the class of rotation-powered pulsars helps constrain models of neutron star spin rates at birth.

N157B was discovered by analysis of data from NASA's Rossi X-rayTiming Explorer (RXTE) ( The results were then confirmed using observations by the joint Japanese/U.S. Advanced Satellite for Cosmology and Astrophysics (ASCA). Further observations will better constrain the age of the pulsar, look for and measure a deceleration of the period and verify the existence of glitches in the emission.

* Crab spindown rate from Zombeck, pg 192, citing Seward, 1978, JBIS 31, pg83
* N157B spindown rate from Wang et al. Volume 494 of the astrophysical Journal

Additional Links

starTake me to the Structure and Evolution of the Universe Press Release on this discovery! (

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