Pulsar
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Pulsars are rotating neutron stars that are observable as sources of electromagnetic radiation. The radiation intensity varies at a regular period, believed to result from the rotation of the star. The pulsar was discovered in 1967, by Jocelyn Bell and Antony Hewish of the University of Cambridge, England. Initially baffled as to the unnaturally regular nature of its emissions, the pair dubbed their discovery LGM-1, for "little green men"; their pulsar was later dubbed CP 1919, and is now known as PSR 1919+21.
CP 1919 emits in radio wavelengths, but pulsars have subsequently been found to emit in the X-ray and gamma ray wavelengths. Along with four others - but not including Jocelyn Bell - Hewish received the 1974 Nobel Prize in Physics for the work.
Three distinct classes of pulsars are presently known to astronomers, according to the source of energy that powers the radiation:
- Rotation-powered pulsars, where the loss of rotational energy of the star powers the radiation
- X-ray pulsars, where the gravitational potential energy of accreted matter is the energy source, and
- Magnetars, where the decay of an extremely strong magnetic field powers the radiation.
Although all three classes of objects are neutron stars, their observable behaviour and the underlying physics are quite different. There are, however, connections. For example, X-ray pulsars are probably old rotation-powered pulsars that have already lost most of their energy, and have only become visible again after their binary companions expanded and began transferring matter on to the neutron star. The process of accretion can in turn transfer enough angular momentum to the neutron star to "recycle" it as a rotation-powered millisecond pulsar.
Significant pulsars
- The first radio pulsar, CP 1919 (now known as PSR B1919+21), with a pulse period of 1.339 seconds and a pulse width of 0.04 second, was discovered in 1967 (Nature 217:709-713, 1968). A drawing of this pulsar's radio waves was used as the cover of British rock band Joy Division's debut album, Unknown Pleasures.
- The first binary pulsar, PSR B1913+16, confirming general relativity and proving the existence of gravitational waves
- The first millisecond pulsar, PSR B1937+21
- The first X-ray pulsar, Cen X-3
- The first millisecond X-ray pulsar, SAX J1808.4-3658
- The first pulsar with planets, PSR B1257+12
- The first double pulsar binary system, PSR J0737−3039
- The magnetar SGR 1806-20 produced the largest burst of energy in the Galaxy ever experimentally recorded on 27 December 2004