Extreme Spinning Tops

摘要

Neutron stars are among the fastest rotating objects in the universe. They have diameters of about 20 km, yet can rotate at up to 43,000 times per second, resulting in speeds at the equator that exceed 10% of the speed of light. On page 1411 of this issue, Archibald et al. (I) provide evidence in support of a long-suspected evolutionary scenario in the formation of such extreme objects. They report observations on a binary neutron star consisting of a "millisecond radio pulsar" with a period of only 1.69 ms and an optically identified low-mass companion. The intriguing and important detail about this binary system is that only a few years ago, it had been identified as a low-mass x-ray binary (LMXB)-a member of the class of systems that were long-believed to bernthe progenitors of millisecond radio pulsars. The reported observations represent the final link in a chain of evidence, which was pieced together over the past 35 years. Moreover, it is one of the rare occasions in which an evolutionary scenario is being played out on a human time scale.