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A radio source from which is received a highly regular train of pulses. As of the end of 2010 nearly 2000 pulsars had been catalogued since the first was discovered in 1967. Pulsars are rapidly spinning neutron stars, 20–30 km in diameter. The stars are highly magnetized (about 108 tesla), with the magnetic axis inclined to the spin axis. The radio emission is believed to arise from the acceleration of charged particles above the magnetic poles. As the star rotates, a beam of radio waves sweeps across the Earth and a pulse is seen, much like the beam from a lighthouse. Pulse periods are typically 1s, but range from 1.4 ms (millisecond pulsars) to over 10 s. The pulse periods are lengthening gradually as the neutron stars lose rotational energy, but a few young pulsars are prone to abrupt disturbances known as glitches. Precise timing of pulses has revealed the existence of binary pulsars, and two pulsars, PSR 1257+12 and PSR B1620-26, have been shown to be accompanied by objects of planetary mass. Optical flashes have been detected from a few pulsars, notably the Crab and Vela Pulsars.

Most pulsars are believed to have been created in supernova explosions by the collapse of the core of a supergiant star, but there is now considerable evidence that at least some of them originate from white dwarfs that have collapsed into neutron stars following accretion of mass from a companion star (see recycled pulsar). The great majority of known pulsars are members of the Milky Way and are concentrated in the galactic plane. There are estimated to be about 100 000 pulsars in the Galaxy. Observations of interstellar dispersion (2) and the Faraday effect in pulsars provides information about the distribution of free electrons and magnetic fields in the Milky Way.

Pulsars are denoted by the prefix PSR followed by the approximate position in right ascension (4 digits) and declination (2 or 3 digits), usually for equinox 1950.0. The figures may be preceded by B if the coordinates are for epoch 1950.0, or J for epoch 2000.0.

http://www.atnf.csiro.au/research/pulsar/psrcat/ Searchable database of all known pulsars, regularly updated.

Subjects: Astronomy and Astrophysics.

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