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millisecond pulsar
A pulsar with a pulse period of less than 25 milliseconds, equivalent to an axial rotation rate of 40 revolutions per second. Such a high spin rate may suggest that these pulsars are young, but in fact the opposite is true. Millisecond pulsars are typically a billion years or more old. They have been rejuvenated by a "spin-up process" involving the accumulation of matter from a companion star. Not only are the periods of millisecond pulsars much shorter than those of normal, young pulsars – the Crab Nebula pulsar, which is the youngest known, has a period of only 0.03 seconds – but their slowdown rate is very low because of their comparatively weak magnetic fields. Indeed, millisecond pulsars are so regular that their pulses can be averaged to create the most accurate clock known to man. Of more than 700 pulsars so far identified, fewer than 20 are of the millisecond variety. The first to be discovered, in 1982, PSR 1937+211, is also the fastest known, completing 642 revolutions per second. In recent years, several confirmed or suspected planets have been found, by pulsar timing, in orbit around millisecond pulsars (see pulsar planets).
Related categories
• TYPES OF STAR
• STELLAR ASTROPHYSICS
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