Schematic view of a pulsar. The sphere in the middle represents the neutron star, the curves indicate the magnetic field lines and the protruding cones represent the emission beams.
Composite Optical/X-ray image of the Crab Nebula, showing synchrotron emission in the surrounding pulsar wind nebula, powered by injection of magnetic fields and particles from the central pulsar. The Crab Nebula  (catalogue designations M 1 NGC 1952 Taurus A is a Supernova remnant and Pulsar wind nebula in the Constellation This article concerns the physical phenomenon of synchrotron radiation A pulsar wind nebula (also known as " plerion " derived from Ancient Greek "pleres" meaning "full" - a term coined by Weiler & Panagia (1978 is

Pulsars are highly magnetized rotating neutron stars which emit a beam of detectable electromagnetic radiation in the form of radio waves. A neutron star is a type of remnant that can result from the Gravitational collapse of a massive Star during a Type II, Type Ib or Type Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. Their observed periods range from 1. 5 ms to 8. 5 s. [1] The radiation can only be observed when the beam of emission is pointing towards the Earth. This is called the lighthouse effect and gives rise to the pulsed nature that gives pulsars their name. Because neutron stars are very dense objects, the rotation period and thus the interval between observed pulses are very regular. For some pulsars, the regularity of pulsation is as precise as an atomic clock. An atomic clock is a type of Clock that uses an Atomic resonance Frequency standard as its timekeeping element [2] Pulsars are known to have planets orbiting them, as in the case of PSR B1257+12. PSR B1257+12, sometimes abbreviated as PSR 1257+12, is a Pulsar located 980 Light-years from the Sun. Werner Becker of the Max-Planck-Institut für extraterrestrische Physik said in 2006, "The theory of how pulsars emit their radiation is still in its infancy, even after nearly forty years of work. The Max Planck Institute for Extraterrestrial Physics is a Max Planck Institute, located in Garching, near Munich, Germany. "[3]

## History

### Discovery

The first pulsar was observed in July 1968 by Jocelyn Bell Burnell and Antony Hewish. Dame Jocelyn Bell Burnell, DBE, FRS, FRAS (born Susan Jocelyn Bell on 15 July 1943) is an astrophysicist Antony Hewish (born Fowey, Cornwall, May 11, 1924) is a British radio astronomer who won the Nobel Prize for Initially baffled as to the seemingly unnatural regularity of its emissions, they dubbed their discovery LGM-1, for "little green men" (a comical name for intelligent beings of extraterrestrial origin). Little green men are the stereotypical portrayal of extraterrestrials as little Humanoid -like creatures with green Extraterrestrial life is Life originating outside of the Earth. Their pulsar was later dubbed CP 1919, and is now known by a number of designators including PSR 1919+21, PSR B1919+21 and PSR J1921+2153. |-! style="background-color #FFFFC0" colspan="2" | Astrometry|- style="vertical-align top"| Spectral type | Pulsar |- style="vertical-align

According to Martin Rees, the hypothesis that pulsars were beacons from extraterrestrial civilizations was never taken very seriously. Martin John Rees Baron Rees of Ludlow, OM, PRS (born 23 June 1942 in York) is an English cosmologist However, astrophysicist Peter A. Sturrock writes that the possibility of an extraterrestrial origin was "seriously considered . Peter Andrew Sturrock (born 1924 is a British scientist An Emeritus professor of Applied physics at Stanford University, much of Sturrock's . . 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)

Although CP 1919 emits in radio wavelengths, pulsars have, subsequently, been found to emit in the X-ray and/or gamma ray wavelengths. Radio waves are electromagnetic waves occurring on the Radio frequency portion of the Electromagnetic spectrum. X-radiation (composed of X-rays) is a form of Electromagnetic radiation. Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions

The word pulsar is a contraction of "pulsating star", and first appeared in print 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 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. " "[4] ”

The suggestion that pulsars were rotating neutron stars was put forth independently by Thomas Gold and Franco Pacini in 1968, and was soon proven beyond doubt by the discovery of a pulsar with a very short (33-millisecond) pulse period in the Crab nebula. Thomas Gold ( May 22, 1920 &ndash June 22, 2004) was an Austrian born Astrophysicist, a professor of Astronomy Year 1968 ( MCMLXVIII) was a Leap year starting on Monday (link will display full calendar of the Gregorian calendar. A millisecond (from Milli- and Second; abbreviation ms is one thousandth of a Second. The Crab Nebula  (catalogue designations M 1 NGC 1952 Taurus A is a Supernova remnant and Pulsar wind nebula in the Constellation

In 1974, Antony Hewish became the first astronomer to be awarded the Nobel Prize in physics. Year 1974 ( MCMLXXIV) was a Common year starting on Tuesday (link will display full calendar of the 1974 Gregorian calendar. The Nobel Prize in Physics (Nobelpriset i fysik is awarded once a year by the Royal Swedish Academy of Sciences. Considerable controversy is associated with the fact that Professor Hewish was awarded the prize while Bell, who made the initial discovery while she was his Ph. D student, was not.

The Vela Pulsar and its surrounding pulsar wind nebula. The Vela Pulsar (PSR B0833-45 or PSR J0835-4510 is a radio optical X-ray and gamma-emitting Pulsar associated with Vela Supernova Remnant, in the Constellation A pulsar wind nebula (also known as " plerion " derived from Ancient Greek "pleres" meaning "full" - a term coined by Weiler & Panagia (1978 is

### Subsequent history

In 1974, Joseph Hooton Taylor, Jr. and Russell Hulse discovered, for the first time, a pulsar in a binary system, PSR B1913+16. Year 1974 ( MCMLXXIV) was a Common year starting on Tuesday (link will display full calendar of the 1974 Gregorian calendar. Joseph Hooton Taylor Jr (born March 29, 1941) is an American Astrophysicist and Nobel Prize in Physics laureate Russell Alan Hulse (born November 28, 1950) is an American Physicist and winner of the Nobel Prize in Physics, shared with his A binary star is a Star system consisting of two Stars orbiting around their Center of mass. PSR B1913+16 (also known as J1915+1606 is a Pulsar in a Binary star system, in orbit with another star around a common center of mass This pulsar orbits another neutron star with an orbital period of just eight hours. Einstein's theory of general relativity predicts that this system should emit strong gravitational radiation, causing the orbit to continually contract as it loses orbital energy. Albert Einstein ( German: ˈalbɐt ˈaɪ̯nʃtaɪ̯n; English: ˈælbɝt ˈaɪnstaɪn (14 March 1879 – 18 April 1955 was a German -born theoretical General relativity or the general theory of relativity is the geometric theory of Gravitation published by Albert Einstein in 1916 In Physics, a gravitational wave is a Fluctuation in the Curvature of Spacetime which propagates as a wave, traveling outward from In Astrodynamics the specific Orbital energy \epsilon\\! (or vis-viva energy) of an Orbiting body traveling through Space Observations of the pulsar soon confirmed this prediction, providing the first ever evidence of the existence of gravitational waves. As of 2004, observations of this pulsar continue to agree with general relativity. "MMIV" redirects here For the Modest Mouse album see " Baron von Bullshit Rides Again " In 1993, the Nobel prize in physics was awarded to Taylor and Hulse for the discovery of this pulsar. Year 1993 ( MCMXCIII) was a Common year starting on Friday (link will display full 1993 Gregorian calendar)

In 1982, a pulsar with a rotation period of just 1. Year 1982 ( MCMLXXXII) was a Common year starting on Friday (link displays the 1982 Gregorian calendar) 6 milliseconds was discovered, by Shri Kulkarni and Don Backer. Shrinivas Kulkarni is a professor of Astrophysics and Planetary science at Caltech. Observations soon revealed that its magnetic field was much weaker than ordinary pulsars, while further discoveries cemented the idea that a new class of object, the "millisecond pulsars" (MSPs) had been found. A millisecond pulsar ( MSP) often referred to as "recycled pulsar", is a Pulsar with a rotational period in the range of about 1-10 Milliseconds MSPs are believed to be the end product of X-ray binaries. X-ray binaries are a class of Binary stars that are luminous in X-rays The X-rays are produced by matter falling from one component (usually a relatively normal Owing to their extraordinarily rapid and stable rotation, MSPs can be used by astronomers as clocks rivalling the stability of the best atomic clocks on Earth. Historically Astronomy was more concerned with the classification and description of phenomena in the sky while Astrophysics attempted to explain these phenomena An atomic clock is a type of Clock that uses an Atomic resonance Frequency standard as its timekeeping element Factors affecting the arrival time of pulses at the Earth by more than a few hundred nanoseconds can be easily detected and used to make precise measurements. A nanosecond ( ns) is one billionth of a second See also times of other orders of magnitude. Physical parameters accessible through pulsar timing include the 3D position of the pulsar, its proper motion, the electron content of the interstellar medium along the propagation path, the orbital parameters of any binary companion, the pulsar rotation period and its evolution with time. The proper motion of a Star is the measurement of its change in position in the sky over time after Improper motions are accounted for The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J (These are computed from the raw timing data by Tempo, a computer program specialized for this task. Tempo is a software program used to analyze radio observations of Pulsars Once enough observations are available Tempo can deduce the pulsar rotation rate and phase astrometric ) After these factors have been taken into account, deviations between the observed arrival times and predictions made using these parameters can be found and attributed to one of three possibilities: intrinsic variations in the spin period of the pulsar, errors in the realization of Terrestrial Time against which arrival times were measured, or the presence of background gravitational waves. Terrestrial Time (TT is the modern astronomical standard for the passage of time on the surface of the Earth (for civil purposes Coordinated Universal Scientists are currently attempting to resolve these possibilities by comparing the deviations seen amongst several different pulsars, forming what is known as a Pulsar Timing Array. With luck, these efforts may lead to a time scale a factor of ten or better than currently available, and the first ever direct detection of gravitational waves.

The first ever extrasolar planets were found orbiting a MSP, by Aleksander Wolszczan. An extrasolar planet, or exoplanet, is a Planet beyond the Solar System, orbiting around other Stars As of September 2008 312 Aleksander Wolszczan (alɛk'sandɛr 'vɔlʂt͡ʂan) ( Apr 29 1946 in Szczecinek, Poland) is a Polish astronomer. This discovery presented important evidence concerning the widespread existence of planets outside the solar system, although it is very unlikely that any life form could survive in the environment of intense radiation near a pulsar. The Solar System consists of the Sun and those celestial objects bound to it by Gravity.

## Pulsar classes

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
• Accretion-powered pulsars (accounting for most but not all 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. Historically Astronomy was more concerned with the classification and description of phenomena in the sky while Astrophysics attempted to explain these phenomena Rotation-powered pulsar is one of the major classes of Pulsars A Rotation-powered pulsar is a rapidly rotating Neutron star, whose Electromagnetic The rotational energy or angular kinetic energy is the Kinetic energy due to the rotation of an object and is part of its total kinetic energy. X-ray pulsars or accretion-powered pulsars are a class of astronomical objects that are X-ray sources displaying strict periodic variations in X-ray intensity X-ray pulsars or accretion-powered pulsars are a class of astronomical objects that are X-ray sources displaying strict periodic variations in X-ray intensity Potential energy can be thought of as Energy stored within a physical system A magnetar is a Neutron star with an extremely powerful Magnetic field, the decay of which powers the emission of copious amounts of high-energy Electromagnetic In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges

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. X-ray pulsars or accretion-powered pulsars are a class of astronomical objects that are X-ray sources displaying strict periodic variations in X-ray intensity A binary star is a Star system consisting of two Stars orbiting around their Center of mass. 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 Physics, the angular momentum of a particle about an origin is a vector quantity equal to the mass of the particle multiplied by the Cross product of the position A millisecond pulsar ( MSP) often referred to as "recycled pulsar", is a Pulsar with a rotational period in the range of about 1-10 Milliseconds

## Naming

Initially pulsars were named with letters of the discovering observatory followed by their right ascension (e. g. CP 1919). As more pulsars were discovered, the letter code became unwieldy and so the convention was then superseded by the letters PSR (Pulsating Source of Radio) followed by the pulsar's right ascension and degrees of declination (e. g. PSR 0531+21) and sometimes declination to a tenth of a degree (e. g. PSR 1913+167). Pulsars that are very close together sometimes have letters appended (e. g. PSR 0021-72C and PSR 0021-72D).

The modern convention is to prefix the older numbers with a B (e. g. PSR B1919+21) with the B meaning the coordinates are for the 1950. 0 epoch. All new pulsars have a J indicating 2000. 0 coordinates and also have declination including minutes (e. g. PSR J1921+2153). Pulsars that were discovered before 1993 tend to retain their B names rather than use their J names (e. g. PSR J1921+2153 is more commonly known as PSR B1919+21). Recently discovered pulsars only have a J name (e. g. PSR J0437-4715). All pulsars have a J name that provides more precise coordinates of its location in the sky. [5]

## Glitch prediction

In June 2006, astronomer John Middleditch and his team at LANL announced the first prediction of glitches with observational data from the Rossi X-ray Timing Explorer. Los Alamos National Laboratory (LANL (previously known at various times as Site Y, Los Alamos Laboratory, and Los Alamos Scientific Laboratory) is a A glitch is a sudden increase (up to 1 part in 106 in the rotational Frequency of a Rotation-powered pulsar, which usually decreases steadily due to braking The Rossi X-ray Timing Explorer ( RXTE) is a satellite that observes the time structure of astronomical x-ray sources They used observations of the pulsar PSR J0537-6910. |- style="vertical-align top"| Distance | 170000 Ly PSR J0537-6910 is a Pulsar that is 4000 years old (plus light travel time

## Applications

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 extrasolar planetary system. In Physics, a gravitational wave is a Fluctuation in the Curvature of Spacetime which propagates as a wave, traveling outward from General relativity or the general theory of relativity is the geometric theory of Gravitation published by Albert Einstein in 1916

### As probes of the interstellar medium

The radiation from pulsars passes through the interstellar medium (ISM) before reaching Earth. Free electrons in the warm (8000 K), ionized component of the ISM and H II regions affect the radiation in two primary ways. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J An H II region (also known as Emission nebula) is a cloud of glowing Gas and plasma, sometimes several hundred Light-years across The resulting changes to the pulsar's radiation provide an important probe of the ISM itself. [6]

Due to the dispersive nature of the interstellar plasma, lower-frequency radio waves travel through the medium faster than higher-frequency radio waves. In Optics, dispersion is the phenomenon in which the Phase velocity of a wave depends on its frequency The resulting delay in the arrival of pulses at a range of frequencies is directly measurable as the dispersion measure of the pulsar. The dispersion measure is the total column density of free electrons between the observer and the pulsar,

$\mathrm{DM} = \int_0^D n_e(s) ds,$

where D is the distance from the pulsar to the observer and ne is the electron density of the ISM. The dispersion measure is used to construct models of the free electron distribution in the Milky Way Galaxy. The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias sometimes referred to simply [7]

Additionally, turbulence in the interstellar gas causes density inhomogeneities in the ISM which cause scattering of the radio waves from the pulsar. In Fluid dynamics, turbulence or turbulent flow is a fluid regime characterized by chaotic Stochastic property changes Scattering is a general physical process whereby some forms of Radiation, such as Light, Sound or moving particles for example are forced to deviate from The resulting scintillation of the radio waves—the same effect as the twinkling of a star in visible light due to density variations in the Earth's atmosphere—can be used to reconstruct information about the small scale variations in the ISM. Scintillation or twinkling are generic terms for rapid variations in apparent brightness or color of a distant luminous object viewed through the atmosphere. [8] Due to the high velocity (up to several hundred km/sec) of many pulsars, a single pulsar scans the ISM rapidly, which results in changing scintillation patterns over timescales of a few minutes. [9]

## Significant pulsars

• The first radio pulsar CP 1919 (now known as PSR 1919+21), with a pulse period of 1. |-! style="background-color #FFFFC0" colspan="2" | Astrometry|- style="vertical-align top"| Spectral type | Pulsar |- style="vertical-align 337 seconds and a pulse width of 0. 04 second, was discovered in 1967 (Nature 217:709-713, 1968). Year 1967 ( MCMLXVII) was a Common year starting on Sunday (link will display full calendar of the 1967 Gregorian calendar. Nature is a prominent Scientific journal, first published on 4 November 1869 Year 1968 ( MCMLXVIII) was a Leap year starting on Monday (link will display full calendar of the Gregorian calendar.
• The first binary pulsar, PSR 1913+16, whose orbit is decaying at the exact rate predicted due to the emission of gravitational radiation by general relativity
• The first millisecond pulsar, PSR B1937+21
• The brightest millisecond pulsar, PSR J0437-4715
• The first X-ray pulsar, Cen X-3
• The first accreting millisecond X-ray pulsar, SAX J1808.4-3658
• The first extrasolar planets to be discovered orbit the pulsar 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[10]
• PSR B1931+24 ". A binary pulsar is a Pulsar with a binary companion, often another Pulsar, White dwarf or Neutron star. In Physics, a gravitational wave is a Fluctuation in the Curvature of Spacetime which propagates as a wave, traveling outward from General relativity or the general theory of relativity is the geometric theory of Gravitation published by Albert Einstein in 1916 Centaurus X-3 (4U 1118-60 is an X-ray pulsar with a period of 4 A transient X-ray source first discovered in 1996 by the Italian-Dutch BeppoSAX satellite SAX J1808 An extrasolar planet, or exoplanet, is a Planet beyond the Solar System, orbiting around other Stars As of September 2008 312 PSR B1257+12, sometimes abbreviated as PSR 1257+12, is a Pulsar located 980 Light-years from the Sun. |- style="vertical-align top"| Distance | 1600 - 2000 Ly (600 Parsecs) PSR J0737-3039 is a binary Pulsar system |- style="vertical-align top"| Distance | 50000 Light-years (14 Events 537 - The Hagia Sophia is completed 1512 - The Spanish Crown issues the Laws of Burgos, governing the "MMIV" redirects here For the Modest Mouse album see " Baron von Bullshit Rides Again " . . 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] braking 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. [11]
• PSR J1748-2446ad, at 716 Hz, the pulsar with the highest rotation speed. |-! style="background-color #FFFFC0" colspan="2" | Astrometry|- style="vertical-align top"| Distance | 18
• PSR J0108-1431, the closest known pulsar to the Earth. It lies in the direction of the constellation Cetus, at a distance of about 85 parsecs (280 light years). Cetus ( Κῆτος Kētos, referring to the sea monster Cetus) is a Constellation of the northern winter sky in the region known as the Water History The first direct measurements of an object at interstellar distances were undertaken by German Astronomer Friedrich Wilhelm Bessel in 1838 A light-year or light year (symbol ly) is a unit of Length, equal to just under ten trillion Kilometres As defined by Nevertheless, it was not discovered until 1993 due to its extremely low luminosity. It was discovered by the Danish astronomer Thomas Tauris[12] in collaboration with a team of Australian and European astronomers using the Parkes 64-meter radio telescope. The pulsar is 1000 times weaker than an average radio pulsar and thus this pulsar may represent the tip of an iceberg of a population of more than half a million such dim pulsars crowding our Milky Way. [13][14]
• PSR J1903+0327, a ~2. PSR J1903+0327 is a millisecond Pulsar in a highly eccentric binary orbit 15 ms pulsar discovered to be in a highly eccentric binary system with a sun-like star[15].

## Notes

1. ^ M. D. Young, R. N. Manchester and S. Johnston. "A radio pulsar with an 8. 5-second period that challenges emission models. " Nature, 400:848-849, 1999.
2. ^ D. N. Matsakis, J. H. Taylor and T. M. Eubanks. "A statistic for describing pulsar and clock stabilities. " A&A, 326:924-928, October 1997.
3. ^ European Space Agency, press release, "Old pulsars still have new tricks to teach us", 26 July 2006
4. ^ Daily Telegraph 5 Mar 1968 21/3
5. ^ Lyne, Andrew G. ; Francis Graham-Smith (1998). Pulsar Astronomy. Cambridge University Press. ISBN 0-521-59413-8.
6. ^ Ferriere, K. (2001). "The Interstellar Environment of our Galaxy". Reviews of Modern Physics 73 (4): 1031-1066. doi:10.1103/RevModPhys.73.1031. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. arXiv:astro-ph/0106359. The arXiv ( pronounced " Archive " as if the "X" were the Greek letter Chi, χ is an Archive for electronic
7. ^ Taylor, J. H. ; Cordes, J. M. (1993). "Pulsar distances and the galactic distribution of free electrons". Astrophysical Journal 411: 674. doi:10.1086/172870. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.
8. ^ Rickett, B. J. (1990). "Radio propagation through the turbulent interstellar plasma". Annual Review of Astronomy and Astrophysics 28: 561. doi:10.1146/annurev.aa.28.090190.003021. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.
9. ^ Rickett, Barney J. ; Lyne, Andrew G. ; Gupta, Yashwant (1997). "Interstellar Fringes from Pulsar B0834+06". Monthly Notices of the Royal Astronomical Society 287: 739.
10. ^ Galactic Magnetar Throws Giant Flare. Astronomy Picture of the Day (2005-02-21). Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. Events 362 - Athanasius returns to Alexandria. 1245 - Thomas, the first known Bishop of Finland Retrieved on 2008-05-23. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 1430 - Siege of Compiègne: Joan of Arc is captured by the Burgundians while leading an army to relieve Compiègne
11. ^ Part-Time Pulsar Yields New Insight Into Inner Workings of Cosmic Clocks. Retrieved on 2008-05-23. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 1430 - Siege of Compiègne: Joan of Arc is captured by the Burgundians while leading an army to relieve Compiègne
12. ^ Tauris, T. M. ; Nicastro, L. ; Johnston, S. ; Manchester, R. N. ; Bailes, M. ; Lyne, A. G. ; Glowacki, J. ; Lorimer, D. R. ; D'Amico, N. (1994). "Discovery of PSR J0108-1431: The closest known neutron star?". Astrophysical Journal 428: L53. Bibcode1994ApJ...428L..53T. The bibcode is an identifier used by a number of astronomical data systems to specify literature references
13. ^ Crowsell, K. "Science: Dim pulsars may crowd our Galaxy", 2008-06-18, p. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 618 - Coronation of the Chinese governor Li Yuan as Emperor Gaozu of Tang, the new Emperor of China, initiating three centuries  16. Retrieved on 2008-05-23. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 1430 - Siege of Compiègne: Joan of Arc is captured by the Burgundians while leading an army to relieve Compiègne
14. ^ "Closest Pulsar?", Sky & Telescope, October 1994, pp.  14.
15. ^ Champion et al, Science , 6 June 2008: Vol. 320. no. 5881, pp. 1309 - 1312 DOI: 10. 1126/science. 1157580

## References

• 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