Pulsar

Encyclopedia : P : PU : PUL : Pulsar

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It has been suggested that this article or section be [Merging and moving pagesmerged] with [Rotation-powered_pulsar], but this suggestion is disputed. ([Discuss])

This article is about the type of neutron star. For other meanings, see Pulsar (disambiguation).

Pulsars are rotating neutron stars that are observable as sources of electromagnetic radiation in radio wavebands. The radiation intensity varies with a regular period, believed to correspond to the rotation period of the star. Pulsars also create what is called the lighthouse effect, this is when the light from a pulsar is only seen at a specific position and not all of the time.

The first pulsar was discovered in 1967, by Jocelyn Bell Burnell 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/or gamma ray wavelengths. Hewish received the 1974 Nobel Prize in Physics for this and related radio astronomy work.

Three distinct classes of pulsars are currently 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 (producing X-rays that are observable from Earth), 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.

In June 2006, astronomer John Middleditch and his team at LANL have announced the first prediction of starquakes, with observational data from Rossi X-ray Timing Explorer. They also are the first to observe the shifting of magnetic poles on a pulsar. They used observations of the pulsar PSR J0537-6910.

The study of pulsars has resulted in many applications in physics and astronomy. Striking examples include the confirmation of the existence of gravitational radiation as predicted by general relativity and the first detection of an extra-solar planetary system.

Significant pulsars

• The first radio pulsar, CP 1919 (now known as PSR 1919+21), with a pulse period of 1.337 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 1913+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.
• PSR B1931+24 "... appears as a normal pulsar for about a week and then 'switches off' for about one month before emitting pulses again. [..] this pulsar slows down more rapidly when the pulsar is on than when it is off. [.. the] breaking mechanism must be related to the radio emission and the processes creating it and the additional slow-down can be explained by a wind of particles leaving the pulsar's magnetosphere and carrying away rotational energy. [link]
• PSR J1748-2446ad, at 716 Hz, the fastest spinning pulsar known

Sources

• Duncan R. Lorimer, "Binary and Millisecond Pulsars at the New Millennium", Living Rev. Relativity 4, (2001), http://www.livingreviews.org/lrr-2001-5
• D. R. Lorimer & M. Kramer; Handbook of Pulsar Astronomy; Cambridge Observing Handbooks for Research Astronomers, 2004
• Ingrid H. Stairs, "Testing General Relativity with Pulsar Timing", Living Rev. Relativity 6, (2003): http://www.livingreviews.org/lrr-2003-5
• 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]
• [The ATNF Pulsar Catalogue]
• [The Discovery of Pulsars] on H2G2
• [04/19/06: XMM-Newton Reveals a Tumbling Neutron Star]
• [04/27/06: Starquake Reveals Hidden Structure of a Neutron Star]
• [Scientists Can Predict Pulsar Starquakes] (SpaceDaily) Jun 07, 2006
• [List of pulsars in binary systems]

See also

• Neutron star
• Radio pulsar
• X-ray pulsar
• Magnetar
• Millisecond pulsar
• Rotating radio transient
• Pulsar planets

 

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