Pulsar

A pulsar (from pulse and -ar as in quasar)[1] is a highly magnetized rotating neutron star or white dwarf that emits a beam of electromagnetic radiation. This radiation can be observed only when the beam of emission is pointing toward Earth (much like the way a lighthouse can be seen only when the light is pointed in the direction of an observer), and is responsible for the pulsed appearance of emission. Neutron stars are very dense, and have short, regular rotational periods. This produces a very precise interval between pulses that ranges from milliseconds to seconds for an individual pulsar. Pulsars are believed to be one of the candidates for the source of ultra-high-energy cosmic rays (see also centrifugal mechanism of acceleration).

The periods of pulsars make them very useful tools. Observations of a pulsar in a binary neutron star system were used to indirectly confirm the existence of gravitational radiation. The first extrasolar planets were discovered around a pulsar, PSR B1257+12. Certain types of pulsars rival atomic clocks in their accuracy in keeping time.[2]

PIA18848-PSRB1509-58-ChandraXRay-WiseIR-20141023
PSR B1509-58X-rays from Chandra are gold; Infrared from WISE in red, green and blue/max.

History of observation

Discovery

Chart Showing Radio Signal of First Identified Pulsar
Chart on which Jocelyn Bell Burnell first recognised evidence of a pulsar, exhibited at Cambridge university Library
Chandra-crab
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 first pulsar was observed on November 28, 1967, by Jocelyn Bell Burnell and Antony Hewish.[3][4][5] They observed pulses separated by 1.33 seconds that originated from the same location in the sky, and kept to sidereal time. In looking for explanations for the pulses, the short period of the pulses eliminated most astrophysical sources of radiation, such as stars, and since the pulses followed sidereal time, it could not be human-made radio frequency interference.

When observations with another telescope confirmed the emission, it eliminated any sort of instrumental effects. At this point, Bell Burnell said of herself and Hewish that "we did not really believe that we had picked up signals from another civilization, but obviously the idea had crossed our minds and we had no proof that it was an entirely natural radio emission. It is an interesting problem—if one thinks one may have detected life elsewhere in the universe, how does one announce the results responsibly?"[6] Even so, they nicknamed the signal LGM-1, for "little green men" (a playful name for intelligent beings of extraterrestrial origin).

It was not until a second pulsating source was discovered in a different part of the sky that the "LGM hypothesis" was entirely abandoned.[7] Their pulsar was later dubbed CP 1919, and is now known by a number of designators including PSR 1919+21 and PSR J1921+2153. Although CP 1919 emits in radio wavelengths, pulsars have subsequently been found to emit in visible light, X-ray, and gamma ray wavelengths.[8]

The word "pulsar" is a portmanteau of 'pulsating' and 'quasar', 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 [star]. 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."[9]

The existence of neutron stars was first proposed by Walter Baade and Fritz Zwicky in 1934, when they argued that a small, dense star consisting primarily of neutrons would result from a supernova.[10] Based on the idea of magnetic flux conservation from magnetic main sequence stars, Lodewijk Woltjer proposed in 1964 that such neutron stars might contain magnetic fields as large as 10^14 to 10^16 G.[11] In 1967, shortly before the discovery of pulsars, Franco Pacini suggested that a rotating neutron star with a magnetic field would emit radiation, and even noted that such energy could be pumped into a supernova remnant around a neutron star, such as the Crab Nebula.[12] After the discovery of the first pulsar, Thomas Gold independently suggested a rotating neutron star model similar to that of Pacini, and explicitly argued that this model could explain the pulsed radiation observed by Bell Burnell and Hewish.[13] The discovery of the Crab pulsar later in 1968 seemed to provide confirmation of the rotating neutron star model of pulsars. The Crab pulsar has a 33-millisecond pulse period, which was too short to be consistent with other proposed models for pulsar emission. Moreover, the Crab pulsar is so named because it is located at the center of the Crab Nebula, consistent with the 1933 prediction of Baade and Zwicky.[14]

In 1974, Antony Hewish and Martin Ryle became the first astronomers to be awarded the Nobel Prize in Physics, with the Royal Swedish Academy of Sciences noting that Hewish played a "decisive role in the discovery of pulsars".[15] Considerable controversy is associated with the fact that Hewish was awarded the prize while Bell, who made the initial discovery while she was his PhD student, was not. Bell claims no bitterness upon this point, supporting the decision of the Nobel prize committee.[16]

Milestones

Vela Pulsar jet
The Vela Pulsar and its surrounding pulsar wind nebula.

In 1974, Joseph Hooton Taylor, Jr. and Russell Hulse discovered for the first time a pulsar in a binary system, PSR B1913+16. 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. Observations of the pulsar soon confirmed this prediction, providing the first ever evidence of the existence of gravitational waves. As of 2010, observations of this pulsar continue to agree with general relativity.[17] In 1993, the Nobel Prize in Physics was awarded to Taylor and Hulse for the discovery of this pulsar.[18]

In 1982, Don Backer led a group which discovered PSR B1937+21, a pulsar with a rotation period of just 1.6 milliseconds (38,500 rpm).[19] 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. MSPs are believed to be the end product of X-ray binaries. Owing to their extraordinarily rapid and stable rotation, MSPs can be used by astronomers as clocks rivaling the stability of the best atomic clocks on Earth. Factors affecting the arrival time of pulses at Earth by more than a few hundred nanoseconds can be easily detected and used to make precise measurements. 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. (These are computed from the raw timing data by Tempo, a computer program specialized for this task.) 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. Scientists are currently attempting to resolve these possibilities by comparing the deviations seen between several different pulsars, forming what is known as a pulsar timing array. The goal of these efforts is to develop a pulsar-based time standard precise enough to make the first ever direct detection of gravitational waves. In June 2006, the astronomer John Middleditch and his team at LANL announced the first prediction of pulsar glitches with observational data from the Rossi X-ray Timing Explorer. They used observations of the pulsar PSR J0537-6910.

In 1992, Aleksander Wolszczan discovered the first extrasolar planets around PSR B1257+12. 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.

In 2016, AR Scorpii was identified as the first pulsar in which the compact object is a white dwarf instead of a neutron star.[20] Because its moment of inertia is much higher than that of a neutron star, the white dwarf in this system rotates once every 1.97 minutes, far slower than neutron-star pulsars.[21] The system displays strong pulsations from ultraviolet to radio wavelengths, powered by the spin-down of the strongly magnetized white dwarf.[20]

Nomenclature

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 then arose of using 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+16.7). Pulsars appearing very close together sometimes have letters appended (e.g. PSR 0021−72C and PSR 0021−72D).

The modern convention prefixes 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.[22]

Formation, mechanism, turn off

Pulsar schematic
Schematic view of a pulsar. The sphere in the middle represents the neutron star, the curves indicate the magnetic field lines, the protruding cones represent the emission beams and the green line represents the axis on which the star rotates.

The events leading to the formation of a pulsar begin when the core of a massive star is compressed during a supernova, which collapses into a neutron star. The neutron star retains most of its angular momentum, and since it has only a tiny fraction of its progenitor's radius (and therefore its moment of inertia is sharply reduced), it is formed with very high rotation speed. A beam of radiation is emitted along the magnetic axis of the pulsar, which spins along with the rotation of the neutron star. The magnetic axis of the pulsar determines the direction of the electromagnetic beam, with the magnetic axis not necessarily being the same as its rotational axis. This misalignment causes the beam to be seen once for every rotation of the neutron star, which leads to the "pulsed" nature of its appearance.

In rotation-powered pulsars, the beam originates from the rotational energy of the neutron star, which generates an electrical field from the movement of the very strong magnetic field, resulting in the acceleration of protons and electrons on the star surface and the creation of an electromagnetic beam emanating from the poles of the magnetic field.[23][24] This rotation slows down over time as electromagnetic power is emitted. When a pulsar's spin period slows down sufficiently, the radio pulsar mechanism is believed to turn off (the so-called "death line"). This turn-off seems to take place after about 10–100 million years, which means of all the neutron stars born in the 13.6 billion year age of the universe, around 99% no longer pulsate.[25]

Though the general picture of pulsars as rapidly rotating neutron stars is widely accepted, Werner Becker of the Max Planck Institute for Extraterrestrial Physics said in 2006, "The theory of how pulsars emit their radiation is still in its infancy, even after nearly forty years of work."[26]

Categories

Three distinct classes of pulsars are currently known to astronomers, according to the source of the power of the electromagnetic radiation:

Although all three classes of objects are neutron stars, their observable behavior and the underlying physics are quite different. There are, however, connections. For example, X-ray pulsars are probably old rotationally-powered pulsars that have already lost most of their power, and have only become visible again after their binary companions had 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. As this matter lands on the neutron star, it is thought to "bury" the magnetic field of the neutron star (although the details are unclear), leaving millisecond pulsars with magnetic fields 1000-10,000 times weaker than average pulsars. This low magnetic field is less effective at slowing the pulsar's rotation, so millisecond pulsars live for billions of years, making them the oldest known pulsars. Millisecond pulsars are seen in globular clusters, which stopped forming neutron stars billions of years ago.[25]

Of interest to the study of the state of the matter in a neutron star are the glitches observed in the rotation velocity of the neutron star. This velocity is decreasing slowly but steadily, except by sudden variations. One model put forward to explain these glitches is that they are the result of "starquakes" that adjust the crust of the neutron star. Models where the glitch is due to a decoupling of the possibly superconducting interior of the star have also been advanced. In both cases, the star's moment of inertia changes, but its angular momentum does not, resulting in a change in rotation rate.

Disrupted recycled pulsar

When two massive stars are born close together from the same cloud of gas, they can form a binary system and orbit each other from birth. If those two stars are at least a few times as massive as our sun, their lives will both end in supernova explosions. The more massive star explodes first, leaving behind a neutron star. If the explosion does not kick the second star away, the binary system survives. The neutron star can now be visible as a radio pulsar, and it slowly loses energy and spins down. Later, the second star can swell up, allowing the neutron star to suck up its matter. The matter falling onto the neutron star spins it up and reduces its magnetic field. This is called "recycling" because it returns the neutron star to a quickly-spinning state. Finally, the second star also explodes in a supernova, producing another neutron star. If this second explosion also fails to disrupt the binary, a double neutron star binary is formed. Otherwise, the spun-up neutron star is left with no companion and becomes a "disrupted recycled pulsar", spinning between a few and 50 times per second.[27]

Applications

The discovery of pulsars allowed astronomers to study an object never observed before, the neutron star. This kind of object is the only place where the behavior of matter at nuclear density can be observed (though not directly). Also, millisecond pulsars have allowed a test of general relativity in conditions of an intense gravitational field.

Maps

Pioneer plaque sun
Relative position of the Sun to the center of the Galaxy and 14 pulsars with their periods denoted

Pulsar maps have been included on the two Pioneer Plaques as well as the Voyager Golden Record. They show the position of the Sun, relative to 14 pulsars, which are identified by the unique timing of their electromagnetic pulses, so that our position both in space and in time can be calculated by potential extraterrestrial intelligences.[28] Because pulsars are emitting very regular pulses of radio waves, its radio transmissions do not require daily corrections. Moreover, pulsar positioning could create a spacecraft navigation system independently, or be used in conjunction with satellite navigation.[29][30]

Precise clocks

Generally, the regularity of pulsar emission does not rival the stability of atomic clocks.[31] However, for some millisecond pulsars, the regularity of pulsation is even more precise than an atomic clock.[32] For example, J0437-4715 has a period of 0.005757451936712637 s with an error of 1.7×10−17 s. This stability allows millisecond pulsars to be used in establishing ephemeris time[33] or in building pulsar clocks.[34]

Timing noise is the name for rotational irregularities observed in all pulsars. This timing noise is observable as random wandering in the pulse frequency or phase.[35] It is unknown whether timing noise is related to pulsar glitches.

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 resulting changes to the pulsar's radiation provide an important probe of the ISM itself.[36]

Because of the dispersive nature of the interstellar plasma, lower-frequency radio waves travel through the medium slower than higher-frequency radio waves. 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,

where is the distance from the pulsar to the observer and is the electron density of the ISM. The dispersion measure is used to construct models of the free electron distribution in the Milky Way.[37]

Additionally, turbulence in the interstellar gas causes density inhomogeneities in the ISM which cause scattering of the radio waves from the pulsar. 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.[38] Due to the high velocity (up to several hundred km/s) of many pulsars, a single pulsar scans the ISM rapidly, which results in changing scintillation patterns over timescales of a few minutes.[39]

Probes of space-time

Pulsars orbiting within the curved space-time around Sgr A*, the supermassive black hole at the center of the Milky Way, could serve as probes of gravity in the strong-field regime.[40] Arrival times of the pulses would be affected by special- and general-relativistic Doppler shifts and by the complicated paths that the radio waves would travel through the strongly curved space-time around the black hole. In order for the effects of general relativity to be measurable with current instruments, pulsars with orbital periods less than about 10 years would need to be discovered;[40] such pulsars would orbit at distances inside 0.01 pc from Sgr A*. Searches are currently underway; at present, five pulsars are known to lie within 100 pc from Sgr A*.[41]

Gravitational waves detectors

There are 3 consortia around the world which use pulsars to search for gravitational waves. In Europe, there is the European Pulsar Timing Array (EPTA); there is the Parkes Pulsar Timing Array (PPTA) in Australia; and there is the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) in Canada and the US. Together, the consortia form the International Pulsar Timing Array (IPTA). The pulses from Millisecond Pulsars (MSPs) are used as a system of Galactic clocks. Disturbances in the clocks will be measurable at Earth. A disturbance from a passing gravitational wave will have a particular signature across the ensemble of pulsars, and will be thus detected.

Significant pulsars

Pulsars within 300 pc[42]
PSR Distance
(pc)
Age
(Myr)
J0030+0451 244 7,580
J0108−1431 238 166
J0437−4715 156 1,590
J0633+1746 156 0.342
J0659+1414 290 0.111
J0835−4510 290 0.0113
J0453+0755 260 17.5
J1045−4509 300 6,710
J1741−2054 250 0.387
J1856−3754 161 3.76
J2144−3933 165 272
Fermi's Gamma-ray Pulsars
Gamma-ray pulsars detected by the Fermi Gamma-ray Space Telescope.

The pulsars listed here were either the first discovered of its type, or represent an extreme of some type among the known pulsar population, such as having the shortest measured period.

  • The first radio pulsar "CP 1919" (now known as PSR B1919+21), with a pulse period of 1.337 seconds and a pulse width of 0.04-second, was discovered in 1967.[43]
  • 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 brightest radio pulsar, the Vela Pulsar.
  • 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 pulsar with planets, PSR B1257+12
  • The first pulsar observed to have been affected by asteroids: PSR J0738-4042
  • The first double pulsar binary system, PSR J0737−3039
  • The shortest period pulsar, PSR J1748-2446ad, with a period of ~0.0014 seconds or ~1.4 milliseconds (716 times a second).
  • The longest period pulsar, at 118.2 seconds, as well as the only known example of a white dwarf pulsar, AR Scorpii.[44]
  • The longest period neutron star pulsar, PSR J0250+5854, with a period of 23.5 seconds.[45]
  • The pulsar with the most stable period, PSR J0437-4715
  • The first millisecond pulsar with 2 stellar mass companions, PSR J0337+1715
  • PSR J1841-0500, stopped pulsing for 580 days. One of only two pulsars known to have stopped pulsing for more than a few minutes.
  • PSR B1931+24, has a cycle. It pulses for about a week and stops pulsing for about a month.[46] One of only two pulsars known to have stopped pulsing for more than a few minutes.
  • PSR J1903+0327, a ~2.15 ms pulsar discovered to be in a highly eccentric binary star system with a Sun-like star.[47]
  • PSR J2007+2722, a 40.8-hertz 'recycled' isolated pulsar was the first pulsar found by volunteers on data taken in February 2007 and analyzed by distributed computing project Einstein@Home.[48]
  • PSR J1311–3430, the first millisecond pulsar discovered via gamma-ray pulsations and part of a binary system with the shortest orbital period.[49]

Gallery

Crab Lucky video2

Video - Crab Pulsar - bright pulse & interpulse.

Video - Artist's impression of AR Scorpii.

See also

Notes

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References and further reading

External links

Bajaj Pulsar

The Bajaj Pulsar is an extremely popular motorcycle brand owned by Bajaj Auto in India. The two wheeler was developed by the product engineering division of Bajaj Auto in association with Tokyo R&D, and later with motorcycle designer Glynn Kerr. Currently there are six variants available, with engine capacities of 135 cc, 150 cc, 160cc, 180 cc, 200 cc and 220 cc .The pulsar 135/150/180/220cc are based on the previous platform which has been in production since it's introduction in 2001 , while the Pulsar 160/200cc are based on the latest platform which incorporates many technological advancement over the previous platforms. mention must be made of a very competitive Pulsar 200 dts-i which was in production for a very short period. The year 2012 marked the arrival of the all new Pulsar platform and the Pulsar 200NS was launched. However Pulsar 200NS production was suspended for some time (reintroduced in early 2017 with BS IV Emission compliance and renamed the NS200). With average monthly sales of around 86,000 units in 2011, Pulsar claimed a 2011 market share of 47% in its segment. By April 2012, more than five million units of Pulsar were sold. In 2018, they celebrated selling over 1 crore Pulsars backed an exclusive TV commercial and a marquee ride to in 6 cities to write "PULSAR" on a pre-defined route.

Before the introduction of the Pulsar, the Indian motorcycle market trend was towards fuel efficient, small capacity motorcycles (that formed the 80–125 cc class). Bigger motorcycles with higher capacity virtually did not exist (except for Royal Enfield Bullet with 350cc and 500cc variants). The launch and success of Hero Honda CBZ in 1999 showed that there was demand for performance bikes. Bajaj took the cue from there on and launched the Pulsar twins (150cc and 180cc) in India on 24 November 2001. Since the introduction and success of Bajaj Pulsar, Indian youth began expecting high power and other features from affordable motorcycles.

The project faced internal resistance, reservations by McKinsey & Company and doubts on its effects on Bajaj's relation with Kawasaki. The project took approximately 36 months for completion and cost Bajaj ₹ 1 billion.

Binary pulsar

A binary pulsar is a pulsar with a binary companion, often a white dwarf or neutron star. (In at least one case, the double pulsar PSR J0737-3039, the companion neutron star is another pulsar as well.) Binary pulsars are one of the few objects which allow physicists to test general relativity because of the strong gravitational fields in their vicinities. Although the binary companion to the pulsar is usually difficult or impossible to observe directly, its presence can be deduced from the timing of the pulses from the pulsar itself, which can be measured with extraordinary accuracy by radio telescopes.

Crab Nebula

The Crab Nebula (catalogue designations M1, NGC 1952, Taurus A) is a supernova remnant in the constellation of Taurus. The now-current name is due to William Parsons, 3rd Earl of Rosse, who observed the object in 1840 using a 36-inch telescope and produced a drawing that looked somewhat like a crab. Corresponding to a bright supernova recorded by Chinese astronomers in 1054, the nebula was observed later by English astronomer John Bevis in 1731. The nebula was the first astronomical object identified with a historical supernova explosion.

At an apparent magnitude of 8.4, comparable to that of Saturn's moon Titan, it is not visible to the naked eye but can be made out using binoculars under favourable conditions. The nebula lies in the Perseus Arm of the Milky Way galaxy, at a distance of about 2.0 kiloparsecs (6,500 ly) from Earth. It has a diameter of 3.4 parsecs (11 ly), corresponding to an apparent diameter of some 7 arcminutes, and is expanding at a rate of about 1,500 kilometres per second (930 mi/s), or 0.5% of the speed of light.

At the center of the nebula lies the Crab Pulsar, a neutron star 28–30 kilometres (17–19 mi) across with a spin rate of 30.2 times per second, which emits pulses of radiation from gamma rays to radio waves. At X-ray and gamma ray energies above 30 keV, the Crab Nebula is generally the brightest persistent source in the sky, with measured flux extending to above 10 TeV. The nebula's radiation allows for the detailed studying of celestial bodies that occult it. In the 1950s and 1960s, the Sun's corona was mapped from observations of the Crab Nebula's radio waves passing through it, and in 2003, the thickness of the atmosphere of Saturn's moon Titan was measured as it blocked out X-rays from the nebula.

The inner part of the nebula is a much smaller pulsar wind nebula that appears as a shell surrounding the pulsar. Some sources consider the Crab Nebula to be an example of both a pulsar wind nebula as well as a supernova remnant, while others separate the two phenomena based on the different sources of energy production and behaviour. For the Crab Nebula, the divisions are superficial but remain meaningful to researchers and their lines of study.

Crab Pulsar

The Crab Pulsar (PSR B0531+21) is a relatively young neutron star. The star is the central star in the Crab Nebula, a remnant of the supernova SN 1054, which was widely observed on Earth in the year 1054. Discovered in 1968, the pulsar was the first to be connected with a supernova remnant.The Crab Pulsar is one of very few pulsars to be identified optically. The optical pulsar is roughly 20 kilometres (12 mi) in diameter and the pulsar "beams" rotate once every 33 milliseconds, or 30 times each second. The outflowing relativistic wind from the neutron star generates synchrotron emission, which produces the bulk of the emission from the nebula, seen from radio waves through to gamma rays. The most dynamic feature in the inner part of the nebula is the point where the pulsar's equatorial wind slams into the surrounding nebula, forming a termination shock. The shape and position of this feature shifts rapidly, with the equatorial wind appearing as a series of wisp-like features that steepen, brighten, then fade as they move away from the pulsar into the main body of the nebula. The period of the pulsar's rotation is slowing by 38 nanoseconds per day due to the large amounts of energy carried away in the pulsar wind.The Crab Nebula is often used as a calibration source in X-ray astronomy. It is very bright in X-rays and the flux density and spectrum are known to be constant, with the exception of the pulsar itself. The pulsar provides a strong periodic signal that is used to check the timing of the X-ray detectors. In X-ray astronomy, 'crab' and 'millicrab' are sometimes used as units of flux density. A millicrab corresponds to a flux density of about 2.4×10−11 erg s−1 cm−2 (2.4×10−14 W m−2) in the 2–10 keV X-ray band, for a "crab-like" X-ray spectrum, which is roughly a powerlaw in photon energy, I = 9.5 E−1.1.

Very few X-ray sources ever exceed one crab in brightness.

Hulse–Taylor binary

PSR B1913+16 (also known as PSR J1915+1606, PSR 1913+16, and the Hulse–Taylor binary after its discoverers) is a pulsar (a radiating neutron star) which together with another neutron star is in orbit around a common center of mass, thus forming a binary star system. PSR 1913+16 was the first binary pulsar to be discovered. It was discovered by Russell Alan Hulse and Joseph Hooton Taylor, Jr., of the University of Massachusetts Amherst in 1974. Their discovery of the system and analysis of it earned them the 1993 Nobel Prize in Physics "for the discovery of a new type of pulsar, a discovery that has opened up new possibilities for the study of gravitation."

Neutron star

A neutron star is the collapsed core of a giant star which before collapse had a total mass of between 10 and 29 solar masses. Neutron stars are the smallest and densest stars, not counting black holes, hypothetical white holes, quark stars and strange stars. Neutron stars have a radius on the order of 10 kilometres (6.2 mi) and a mass lower than 2.16 solar masses. They result from the supernova explosion of a massive star, combined with gravitational collapse, that compresses the core past white dwarf star density to that of atomic nuclei.

Once formed, they no longer actively generate heat, and cool over time; however, they may still evolve further through collision or accretion. Most of the basic models for these objects imply that neutron stars are composed almost entirely of neutrons (subatomic particles with no net electrical charge and with slightly larger mass than protons); the electrons and protons present in normal matter combine to produce neutrons at the conditions in a neutron star. Neutron stars are partially supported against further collapse by neutron degeneracy pressure, a phenomenon described by the Pauli exclusion principle, just as white dwarfs are supported against collapse by electron degeneracy pressure. However neutron degeneracy pressure is not sufficient to hold up an object beyond 0.7M☉ and repulsive nuclear forces play a larger role in supporting more massive neutron stars. If the remnant star has a mass exceeding the Tolman–Oppenheimer–Volkoff limit, it continues collapsing to form a black hole.

Neutron stars that can be observed are very hot and typically have a surface temperature of around 600000 K. They are so dense that a normal-sized matchbox containing neutron-star material would have a weight of approximately 3 billion metric tons, the same weight as a 0.5 cubic kilometre chunk of the Earth (a cube with edges of about 800 metres). Their magnetic fields are between 108 and 1015 (100 million to 1 quadrillion) times stronger than Earth's magnetic field. The gravitational field at the neutron star's surface is about 2×1011 (200 billion) times that of Earth's gravitational field.

As the star's core collapses, its rotation rate increases as a result of conservation of angular momentum, hence newly formed neutron stars rotate at up to several hundred times per second. Some neutron stars emit beams of electromagnetic radiation that make them detectable as pulsars. Indeed, the discovery of pulsars by Jocelyn Bell Burnell in 1967 was the first observational suggestion that neutron stars exist. The radiation from pulsars is thought to be primarily emitted from regions near their magnetic poles. If the magnetic poles do not coincide with the rotational axis of the neutron star, the emission beam will sweep the sky, and when seen from a distance, if the observer is somewhere in the path of the beam, it will appear as pulses of radiation coming from a fixed point in space (the so-called "lighthouse effect"). The fastest-spinning neutron star known is PSR J1748-2446ad, rotating at a rate of 716 times a second or 43,000 revolutions per minute, giving a linear speed at the surface on the order of 0.24 c (i.e. nearly a quarter the speed of light).

There are thought to be around 100 million neutron stars in the Milky Way, a figure obtained by estimating the number of stars that have undergone supernova explosions. However, most are old and cold, and neutron stars can only be easily detected in certain instances, such as if they are a pulsar or part of a binary system. Slow-rotating and non-accreting neutron stars are almost undetectable; however, since the Hubble Space Telescope detection of RX J185635−3754, a few nearby neutron stars that appear to emit only thermal radiation have been detected. Soft gamma repeaters are conjectured to be a type of neutron star with very strong magnetic fields, known as magnetars, or alternatively, neutron stars with fossil disks around them.Neutron stars in binary systems can undergo accretion which typically makes the system bright in X-rays while the material falling onto the neutron star can form hotspots that rotate in and out of view in identified X-ray pulsar systems. Additionally, such accretion can "recycle" old pulsars and potentially cause them to gain mass and spin-up to very fast rotation rates, forming the so-called millisecond pulsars. These binary systems will continue to evolve, and eventually the companions can become compact objects such as white dwarfs or neutron stars themselves, though other possibilities include a complete destruction of the companion through ablation or merger. The merger of binary neutron stars may be the source of short-duration gamma-ray bursts and are likely strong sources of gravitational waves. In 2017, a direct detection (GW170817) of the gravitational waves from such an event was made, and gravitational waves have also been indirectly detected in a system where two neutron stars orbit each other.

In October 2018, astronomers reported that GRB 150101B, a gamma-ray burst event detected in 2015, may be directly related to the historic GW170817 and associated with the merger of two neutron stars. The similarities between the two events, in terms of gamma ray, optical and x-ray emissions, as well as to the nature of the associated host galaxies, are "striking", suggesting the two separate events may both be the result of the merger of neutron stars, and both may be a kilonova, which may be more common in the universe than previously understood, according to the researchers.

Nissan EXA

The Nissan Pulsar EXA and Nissan EXA are automobiles manufactured and marketed by Nissan Motor Company from 1982 to 1986 and from 1986 to 1990 respectively. The first generation model was internally designated as the N12 series and was marketed in Japan at Nissan Cherry Store locations as the Pulsar EXA, and at Nissan Prince Store outlets as the Langley EXA. The second generation EXA was designated as the N13 series.

Both generations were marketed in North America under the name Nissan Pulsar NX.

Nissan Pulsar

The Nissan Pulsar is a subcompact and compact car produced by the Japanese automaker Nissan from 1978 until 2000, when it was replaced by the Nissan Bluebird Sylphy in the Japanese market. Between 2000 and 2005, the name "Pulsar" has been used in Australia and New Zealand on rebadged versions of the Sylphy. This arrangement continued until the introduction of the Nissan Tiida (C11) in 2005; at this time the Pulsar name was retired. In 2013, Nissan replaced the Tiida in Australia and New Zealand with two new models badged as Pulsar. These were based on the Nissan Sylphy (B17) sedan and Nissan Tiida (C12) hatchback, the latter also sold in Thailand under the Pulsar name. In 2014, a European-only replacement for the Tiida was introduced using the Pulsar nameplate.

The original Pulsar was a hatchback to be sold exclusively at a different Nissan Japan dealership network called Nissan Cherry Store as a larger five-door hatchback alternative to the Nissan Cherry. Although Pulsar models were front-wheel drive from introduction, Nissan did offer four-wheel drive as an option on select models internationally.

The Pulsar sold in Japan originally served as the intermediate model offered at Nissan dealerships Nissan Cherry Store between the Nissan Violet and the Cherry, while different versions of the Pulsar sold at other Japanese networks served as the base model, with other larger Nissan products. Various Pulsar-based models were exported as international market conditions dictated, sometimes labeled as "Sunny", "Cherry" or "Sentra", while the internationally labeled product was actually a Pulsar and not a Japanese market Sunny or Cherry.

A pulsar (portmanteau of pulsating star) is a highly magnetized, rotating neutron star, as the Nissan Pulsar was built from the Sunny sedan.

Poulsard

Poulsard (also Ploussard) is a red French wine grape variety from the Jura wine region. The name Ploussard is used mainly around the town of Pupillin but can appear on wine labels throughout Jura as an authorized synonyms. While technically a dark-skinned noir grape, the skins of Poulsard are very thin with low amounts of color -phenols and produces very pale colored red wines, even with extended maceration and can be used to produce white wines. Because of this, Poulsard is often blended with other red-skin varieties or used to produce lightly colored rosé wines. Additionally the grape is used to make blanc de noir white wines and sparkling cremants.Poulsard is an authorized grape variety in the Appellation d'Origine Contrôlée (AOC) wines of Arbois AOC, Côtes du Jura AOC, Crémant du Jura AOC, L'Etoile AOC and Macvin du Jura AOC. Outside Jura, Poulsard is also grown in Bugey AOC of the Ain département in eastern France.

Pulsar (watch)

Pulsar is a brand of watch and currently a division of Seiko Watch Corporation of America (SCA). Pulsar was the world's first electronic digital watch. Today Pulsar watches are mostly analog and use the same movements in Seikos such as the 7T62 quartz chronograph movement.

Pulsar Stargrave

Pulsar Stargrave is a fictional supervillain featured in DC Comics as a foe of the Legion of Super-Heroes.

Pulsar planet

Pulsar planets are planets that are found orbiting pulsars, or rapidly rotating neutron stars. The first such planet to be discovered was around a millisecond pulsar and was the first extrasolar planet to be confirmed as discovered.

Pulsar timing array

A pulsar timing array (PTA) is a set of pulsars which is analyzed to search for correlated signatures in the pulse arrival times. There are many applications for pulsar timing arrays. The most well known is to use an array of millisecond pulsars to detect and analyse gravitational waves. Such a detection would result from a detailed investigation of the correlation between arrival times of pulses emitted by the millisecond pulsars as a function of the pulsars' angular separations.

Pulsar wind nebula

A pulsar wind nebula (PWN, plural PWNe), sometimes called a plerion (derived from the Greek "πλήρης", pleres, meaning "full"), is a type of nebula found inside the shells of supernova remnants (SNRe) that is powered by pulsar winds generated by its central pulsar. These nebulae were discovered in 1976 as small depressions at radio wavelengths near the centre of supernova remnants. They have since been found to be X-ray emitters and are possibly gamma ray sources.

Russell Alan Hulse

Russell Alan Hulse (born November 28, 1950) is an American physicist and winner of the Nobel Prize in Physics, shared with his thesis advisor Joseph Hooton Taylor Jr., "for the discovery of a new type of pulsar, a discovery that has opened up new possibilities for the study of gravitation". He was a specialist in the pulsar studies and gravitational waves.

X-ray pulsar

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. The X-ray periods range from as little as a fraction of a second to as much as several minutes.

X-ray pulsar-based navigation

X-ray pulsar-based navigation and timing (XNAV) or simply pulsar navigation is a navigation technique whereby the periodic X-ray signals emitted from pulsars are used to determine the location of a vehicle, such as a spacecraft in deep space. A vehicle using XNAV would compare received X-ray signals with a database of known pulsar frequencies and locations. Similar to GPS, this comparison would allow the vehicle to triangulate its position accurately (±5 km). The advantage of using X-ray signals over radio waves is that X-ray telescopes can be made smaller and lighter. Experimental demonstrations have been reported in 2018.

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