Pulsar
From Freepedia
Pulsars are rotating neutron stars that are observable as sources of electromagnetic radiation. The radiation intensity varies with a regular period, believed to correspond to the rotation period of the star.
The first pulsar was discovered in 1967, by Jocelyn Bell and Antony Hewish of the University of Cambridge, UK. 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 by a number of designators including PSR 1919+21. Astrophysicist Peter A. Sturrock writes that "when the first regular radio signals from pulsars were discovered, the Cambridge scientists seriously considered that they might have come from an extraterrestrial civilization. They debated this possibility and decided that, if this proved to be correct, they could not make an announcement without checking with higher authorities. There was even some discussion about whether it might be in the best interests of mankind to destroy the evidence and forget it!" (Sturrock, 154)
CP 1919 emits in radio wavelengths, but pulsars have subsequently been found to emit in the X-ray and gamma ray wavelengths. Hewish received the 1974 Nobel Prize in Physics for this and related radio astronomy 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.
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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
- The pulsar PSR B0950+08 seems to have come from a supernova that occurred in Antlia Pneumatica 1.8 million years ago. The remnant of this supernova may be the nearest besides the Local Bubble, and the supernova would have been as bright as the moon.
Sources
- Peter A. Sturrock; The UFO Enigma: A New Review of the Physical Evidence; Warner Books, 1999; ISBN 0446525650
External links
- A Pulsar Discovery - the detection of the first optical pulsar from the American Institute of Physics. Includes audio and teachers guides.
- The listing for the first pulsar (PULS CP 1919) in the Simbad database
