Millisecond Pulsars

As the name suggestions, millisecond pulsars have pulse periods that are in the range from one to ten milliseconds.

The first millisecond pulsar designated PSR 1937+21 (by its coordinates), was discovered by Backer and his colleagues using the Arecibo telescope in 1982. This pulsar has a pulse period of 1.6 milliseconds; the neutron star is rotating an amazing 640 times each second. Yet it has a mass of about 1.4 solar masses!

Until the discovery of PSR 1937+21, the fastest known pulsar was the 33 ms pulsar associated with the Crab Nebula. Conventional wisdom argued that since pulsars were expected to slow their rotation with time. Since the Crab is known to have been a supernova only 1000 years ago, in 1054 A.D., it is very young and therefore should have a very short period. Therefore, pulsars with shorter periods were not predicted by what was understood at the time.

Curiously, timing of the millisecond pulsar showed that not only is it rotating very fast, its slow down rate, dubbed P-dot, is extremely small, less than 2 x 10-19 seconds per second. The fact that astronomers can detect such a slowdown is pretty amazing! Therefore, the previous relationship between the age of the pulsar since its formation by a supernova and the slow down rate does not seem to hold. Instead, it has been hypothesized that the millisecond pulsars must be "spun-up" by some external mechanism

Check out the multimedia link maintained by the Princeton pulsar group.


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