Evidence for free precession in a pulsar

摘要: Pulsars are rotating neutron stars that produce lighthouse-like beams of radio emission from their magnetic poles. The observed pulse enables rotation rates to be measured with great precision. For some young pulsars, this provides a means studying the interior structure stars. Most pulsars have stable shapes, and slow down steadily (for example, see ref. 20). Here we report discovery long-term, highly periodic correlated variations in both shape rate slow-down pulsar PSR B1828-11. best described as harmonically related sinusoids, periods approximately 1,000, 500 250 days, probably resulting precession spin axis caused by an asymmetry pulsar. This is difficult understand theoretically, because torque-free solitary should damped out vortices its superfluid interior.