Pulsar
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Pulsars are neutron stars that turn quickly and produce electromagnetic radiation that can be received in the form of radio waves. The strength of radiation changes according to a regular period of time, which is thought to match to the period of time in which the star turns. Pulsars also show a so-called lighthouse effect, which occurs when the light and other radiation from a pulsar are only seen at certain periods of time and not all of the time. Werner Becker of the Max-Planck-Institut für extraterrestrische Physik recently said,
- "The theory of how pulsars emit their radiation is still in its infancy, even after nearly forty years of work.. There are many models but no accepted theory."[1] In other words, scientists are still just beginning to understand pulsars and they do not all agree on how pulsars work.
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[change] Discovery
The first pulsar was discovered in 1967, by w:en:Jocelyn Bell Burnell and w:en:Antony Hewish of the w:en:University of Cambridge, UK.[2] At first, they did not understand why pulsars have a regular change in the strength of radiation, they called their discovery LGM-1, for "w:en:little green men"; their pulsar was later called w:en:CP 1919, and is now known by a number of names including PSR 1919+21. The word pulsar is short for "pulsating star", and was first seen written in 1968:
- "An entirely novel kind of star... came to light on Aug. 6 last year and, ... was referred to by astronomers as LGM (Little Green Men). Now... it is thought to be a novel type between a white dwarf and a neutron [sic]. The name Pulsar (Pulsating Star) is likely to be given to it. ... Dr. A. Hewish ... told me yesterday: '... I am sure that today every radio telescope is looking at the Pulsars."[3] That is to say, this is a new kind of star that is somewhere between a white dwarf and a neutron star.
w:en:Astrophysicist w:en: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 w:en: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) That is to say, when pulsars were discovered, the scientists thought they might be signals from another planet, and the news might be dangerous to society.
CP 1919 produces radio wavelengths, but pulsars have later been found to produce radiation in the X-ray and/or w:en:gamma ray wavelengths. Hewish received the 1974 Nobel Prize in Physics for this and similar work about radio astronomy.
[change] Kinds of pulsars
Astronomers know that there are three different kinds of pulsars, named by the source of energy that powers the radiation:
- w:en:Rotation-powered pulsars, where the radiation is caused by the loss of w:en:rotational energy; radiation is caused by the neutron star slowing down in the speed in which it turns
- Accretion-powered pulsars (which are most but not all w:en:X-ray pulsars), where the gravitational potential energy of matter that falls onto the pulsar causes X-rays that can be received from Earth, and
- w:en:Magnetars, where an extremely strong magnetic field loses energy, which causes the radiation.
Although all three kinds of objects are neutron stars, the things that they can be seen to do and the physics that causes this are very different. But there are some things that are similar. For example, w:en:X-ray pulsars are probably old rotation-powered pulsars that have already lost most of their energy, and can only be seen again after their binary companions expanded and matter from them started falling onto the neutron star. The process of accretion (matter falling onto the neutron star) can in turn give enough w:en:angular momentum energy to the neutron star to change it into a rotation-powered w:en:millisecond pulsar.
[change] Forecasting of glitches
In June 2006, astronomer w:en:John Middleditch and his team at w:en:LANL was the first to forecast glitches (a sudden increase in the speed the star turns), with information that they received from the w:en:Rossi X-ray Timing Explorer. They used information received from the pulsar w:en:PSR J0537-6910.
[change] How the information was used
The study of pulsars has resulted in many uses in physics and astronomy. Major examples include the proof of w:en:gravitational radiation as forecasted by general relativity and the first proof of planets around other stars.
[change] Important pulsars
- The first radio pulsar, w:en:CP 1919 (now called w:en:PSR 1919+21), with a signal that repeats 1.337 seconds with a strong signal that lasts 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 first album, w:en:Unknown Pleasures.
- The first w:en:binary pulsar, w:en:PSR 1913+16, that proves general relativity and proves that gravitational waves exist
- The first millisecond pulsar, w:en:PSR B1937+21
- The first X-ray pulsar, w:en:Cen X-3
- The first accreting millisecond X-ray pulsar, w:en:SAX J1808.4-3658
- The first pulsar with planets, w:en:PSR B1257+12
- The first double pulsar binary system, PSR J0737−3039
- The magnetar w:en:SGR 1806-20 produced the largest burst of energy in the Galaxy ever seen in an experiment on 27 December 2004
- PSR B1931+24 "... looks like a normal pulsar for about a week and then 'switches off' for about one month before producing pulses again. [..] this pulsar slows down more rapidly when the pulsar is on than when it is off. [.. the] way it slows down must have to do with the radio energy and the things that cause it, and the extra slow-down can be explained by a wind of particles leaving the pulsar's magnetic field and slowing down the speed at which it turns. [1]
- w:en:PSR J1748-2446ad, at 716 Hz (times it turns per second), the fastest turning pulsar known
[change] Notes
- ↑ European Space Agency, press release, "Old pulsars still have new tricks to teach us", 26 July 2006
- ↑ Hewish, A.; Bell, S. J.; Pilkington, J. D.; Scott, P. F.; Collins, R. A., "Observation of a Rapidly Pulsating Radio Source" (1968) Nature, Vol. 217, pp. 709
- ↑ Daily Telegraph 5 Mar 1968 21/3
[change] 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 0-446-52565-0
[change] Other websites
- 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 w:en:H2G2
- Scientists Can Predict Pulsar Starquakes (SpaceDaily) Jun 07, 2006
- List of pulsars in binary systems
- XMM-Newton Makes New Discoveries About Old Pulsars (SpaceDaily) Jul 27, 2006
- Hot New Idea: How Dead Stars Go Cold Ker Than (SPACE.com) 27 July 2006 06:16 am ET
[change] See also
