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.


An X-ray pulsar consists of a magnetized neutron star in orbit with a normal stellar companion and is a type of binary star system. The magnetic-field strength at the surface of the neutron star is typically about 108 Tesla, over a trillion times stronger than the strength of the magnetic field measured at the surface of the Earth (60 µT).

Gas is accreted from the stellar companion and is channeled by the neutron star's magnetic field on to the magnetic poles producing two or more localized X-ray hot spots, similar to the two auroral zones on Earth, but far hotter. At these hotspots the infalling gas can reach half the speed of light before it impacts the neutron star surface. So much gravitational potential energy is released by the infalling gas, that the hotspots, which are estimated to about one square kilometer in area, can be ten thousand times, or more, as luminous than the Sun.[1]

Temperatures of millions of degrees are produced so the hotspots emit mostly X-rays. As the neutron star rotates, pulses of X-rays are observed as the hotspots move in and out of view if the magnetic axis is tilted with respect to the spin axis.[1]

Gas supply

The gas that supplies the X-ray pulsar can reach the neutron star by a variety of ways that depend on the size and shape of the neutron star's orbital path and the nature of the companion star.

Some companion stars of X-ray pulsars are very massive young stars, usually OB supergiants (see stellar classification), that emit a radiation driven stellar wind from their surface. The neutron star is immersed in the wind and continuously captures gas that flows nearby. Vela X-1 is an example of this kind of system.

In other systems, the neutron star orbits so closely to its companion that its strong gravitational force can pull material from the companion's atmosphere into an orbit around itself, a mass transfer process known as Roche lobe overflow. The captured material forms a gaseous accretion disc and spirals inwards to ultimately fall onto the neutron star as in the binary system Cen X-3.

For still other types of X-ray pulsars, the companion star is a Be star that rotates very rapidly and apparently sheds a disk of gas around its equator. The orbits of the neutron star with these companions are usually large and very elliptical in shape. When the neutron star passes nearby or through the Be circumstellar disk, it will capture material and temporarily become an X-ray pulsar. The circumstellar disk around the Be star expands and contracts for unknown reasons, so these are transient X-ray pulsars that are observed only intermittently, often with months to years between episodes of observable X-ray pulsation.[2]

Spin behaviors

Radio pulsars (rotation-powered pulsars) and X-ray pulsars exhibit very different spin behaviors and have different mechanisms producing their characteristic pulses although it is accepted that both kinds of pulsar are manifestations of a rotating magnetized neutron star. The rotation cycle of the neutron star in both cases is identified with the pulse period.

The major differences are that radio pulsars have periods on the order of milliseconds to seconds, and all radio pulsars are losing angular momentum and slowing down. In contrast, the X-ray pulsars exhibit a variety of spin behaviors. Some X-ray pulsars are observed to be continuously spinning faster and faster or slower and slower (with occasional reversals in these trends) while others show either little change in pulse period or display erratic spin-down and spin-up behavior.[2]

The explanation of this difference can be found in the physical nature of the two pulsar classes. Over 99% of radio pulsars are single objects that radiate away their rotational energy in the form of relativistic particles and magnetic dipole radiation, lighting up any nearby nebulae that surround them. In contrast, X-ray pulsars are members of binary star systems and accrete matter from either stellar winds or accretion disks. The accreted matter transfers angular momentum to (or from) the neutron star causing the spin rate to increase or decrease at rates that are often hundreds of times faster than the typical spin down rate in radio pulsars. Exactly why the X-ray pulsars show such varied spin behavior is still not clearly understood.


X-ray pulsars are observed using X-ray telescopes that are satellites in low Earth orbit although some observations have been made, mostly in the early years of X-ray astronomy, using detectors carried by balloons or sounding rockets. The first X-ray pulsar to be discovered was Centaurus X-3, in 1971 with the Uhuru X-ray satellite.[1]

See also


  1. ^ a b c Exploring the X-ray Universe, Philip. A. Charles, Frederick D. Seward, Cambridge University Press, 1995, Chap. 7.
  2. ^ a b Bildsten, L.; Chakrabarty, D.; Chu, J.; Finger, M. H.; Koh, D. T.; Nelson, R. W.; Prince, T. A.; Rubin, B. C.; Scott, D. M.; Vaughan, B.; Wilson, C. A.; Wilson, R. B. (1997). "Observations of Accreting Pulsars". The Astrophysical Journal Supplement Series. 113: 367–408. arXiv:astro-ph/9707125. Bibcode:1997ApJS..113..367B. doi:10.1086/313060.

External links


AXP may refer to:

The Cisco Systems Application eXtension Platform, a terminated product

Alpha AXP, now known as DEC Alpha, a 64-bit instruction set architecture developed by Digital Equipment Corporation (DEC), designed to replace their 32-bit VAX

In astronomy, as an abbreviation for Anomalous X-ray pulsar

the NYSE ticker symbol for American Express

The National Rail code for Alexandra Parade railway station, United Kingdom

The Greek letters for the National Fraternity of Alpha Chi Rho (ΑΧΡ)

Automotive X PRIZE

In webcasting, an abbreviation for The Atheist Experience

AXP 1E 1048-59

Anomalous X-ray pulsar (AXP) 1E 1048.1-5937 was the first AXP ever observed to emit an SGR-like X-ray burst. It is also the closest magnetar to Earth.

Anomalous X-ray pulsar

Anomalous X-ray Pulsars (AXPs) are now widely believed to be magnetars—young, isolated, highly magnetized neutron stars. These energetic X-ray pulsars are characterized by slow rotation periods of ~2–12 seconds and large magnetic fields of ~1013–1015 gauss (1 to 100 gigateslas). There are currently (as of 2017) 12 confirmed and 2 candidate AXPs. The identification of AXPs with magnetars was motivated by their similarity to another enigmatic class of sources, the soft gamma repeaters.

Bursting Pulsar

The Bursting Pulsar (GRO J1744-28) is a low-mass x-ray binary with a period of 11.8 days. It was discovered in December 1995 by the Burst and Transient Source Experiment on the Compton Gamma-Ray Observatory, the second of the NASA Great Observatories. The pulsar is unique in that it has a "bursting phase" where it emits gamma rays and X-rays peaking at approximately 20 bursts per hour after which the frequency of bursts drops off and the pulsar enters a quiescent phase. After a few months, the bursts reappear, though not yet with predictable regularity.The Bursting Pulsar is the only known X-ray pulsar that is also a Type II X-ray burster.

CXOU J164710.2−455216

CXOU J164710.2−455216 is an anomalous X-ray pulsar in the massive galactic open cluster Westerlund 1. It is the brightest X-ray source in the cluster, and was discovered

in 2005 in observations made by the Chandra X-ray observatory. The Westerlund 1 cluster is believed to have formed in a single burst of star formation, implying that the progenitor star must have had a mass in excess of 40 solar masses. The fact that a neutron star was formed instead of a black hole implies that more than 95% of the star's original mass must have been lost before or during the supernova that produced the magnetar.On 21 September 2006 the Swift satellite detected a 20ms soft Gamma-ray burst in Westerlund 1. Fortuitously, XMM-Newton observations had been made four days earlier, and repeat observations 1.5 days after the burst revealed the magnetar to be the source of the burst, with the X-ray luminosity increasing by a factor of 100 during the outburst.

Centaurus X-3

Centaurus X-3 (4U 1118-60) is an X-ray pulsar with a period of 4.84 seconds. It was the first X-ray pulsar to be discovered, and the third X-ray source to be discovered in the constellation Centaurus. The system consists of a neutron star orbiting a massive, O-type supergiant star dubbed Krzeminski's star after its discoverer, Wojciech Krzemiński. Matter is being accreted from the star onto the neutron star, resulting in X-ray emission.


Hakucho (also known as CORSA-b before launch) was Japan's first X-ray astronomy satellite, developed by the Institute of Space and Aeronautical Science (then a division of the University of Tokyo). It was launched by the ISAS M-3C-4 rocket on February 21, 1979 and reentered the atmosphere on April 16, 1985.

It was a replacement for the CORSA satellite which failed to launch due to rocket failure on February 4, 1976.

Index of physics articles (X)

The index of physics articles is split into multiple pages due to its size.

To navigate by individual letter use the table of contents below.

List of stars in Tucana

This is the list of notable stars in the constellation Tucana, sorted by decreasing brightness.

M82 X-2

M82 X-2 is an X-ray pulsar located in the galaxy Messier 82, approximately 12 million light-years from Earth. It is exceptionally luminous, radiating energy equivalent to approximately ten million Suns. This object is part of a binary system: If the pulsar is of an average size, 1.4 M☉, then its companion is at least 5.2 M☉. On average, the pulsar rotates every 1.37 seconds, and revolves around its more massive companion every 2.5 days.M82 X-2 is an ultraluminous X-ray source (ULX), shining about 100 times brighter than theory suggests something of its mass should be able to. Its brightness is many times higher than the Eddington limit, a basic physics guideline that sets an upper limit on the brightness that an object of a given mass should be able to achieve. Possible explanations for violations of the Eddington limit include geometrical effects arising from the funneling of in-falling material along magnetic field lines.

While M82 X-2 was previously known as an X-ray source, it was not until an observation campaign to study the newly discovered supernova SN 2014J in January 2014 that X-2's true nature was uncovered. Scientists looking at data from the NuSTAR spacecraft noticed a pulsing in the X-ray spectrum coming from near the supernova in Messier 82. Data from the Chandra and Swift spacecraft was used to verify the NuSTAR findings and provide the necessary spatial resolution to determine the exact source. After combining the NuSTAR and Chandra data, scientists were able to discern that M82 X-2 emitted both an X-ray beam and continuous broad X-ray radiation.

Michiel van der Klis

Michiel Baldur Maximiliaan van der Klis (born 9 June 1953) is a Dutch astronomer best known for his work on extreme 'pairings' of stars called X-ray binaries, more particularly his explanation of the occurrence of quasi-periodic oscillations (QPOs) in these systems and his co-discovery of the first millisecond X-ray pulsar. In the 1980s he gained worldwide fame with his investigation of QPOs. His revolutionary discoveries have had an enormous impact in his field of research; in effect, they have made it what it is today. Van der Klis pioneered special mathematical analysis techniques that are now regarded as the “gold standard” within his discipline.

Neutron Star Interior Composition Explorer

The Neutron star Interior Composition Explorer (NICER) is a NASA Explorers program Mission of Opportunity dedicated to the study of the extraordinary gravitational, electromagnetic, and nuclear physics environments embodied by neutron stars, exploring the exotic states of matter where density and pressure are higher than in atomic nuclei. NICER will enable rotation-resolved spectroscopy of the thermal and non-thermal emissions of neutron stars in the soft (0.2–12 keV) X-ray band with unprecedented sensitivity, probing interior structure, the origins of dynamic phenomena, and the mechanisms that underlie the most powerful cosmic particle accelerators known. NICER will achieve these goals by deploying, following launch, an X-ray timing and spectroscopy instrument as an attached payload aboard the International Space Station (ISS). NICER was selected by NASA to proceed to formulation phase in April 2013.NICER-SEXTANT uses the same instrument to test X-ray timing for positioning and navigation, and MXS is a test of X-ray timing communication. In January 2018, X-ray navigation was demonstrated using NICER on ISS.

PSR B1509−58

PSR B1509−58 is a pulsar approximately 17,000 light-years away in the constellation of Circinus discovered by the Einstein X-Ray Observatory in 1982. It appears approximately 1,700 years old, and it sits in a nebula that spans about 150 light years. NASA described the star as "a rapidly spinning neutron star which is spewing energy out into the space around it to create complex and intriguing structures, including one that resembles a large cosmic hand." Which is also known by name "Hand of God". Spin rate is "almost 7 times per second".


A pulsar (from pulse and -ar as in quasar) 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.

SN 1181

First observed between August 4 and August 6, 1181, Chinese and Japanese astronomers recorded the supernova now known as SN 1181 in eight separate texts.

One of only eight supernovae in the Milky Way observable with the naked eye in recorded history, it appeared in the constellation Cassiopeia and was visible in the night sky for about 185 days.

The radio and X-ray pulsar J0205+6449 (also known as 3C 58), which rotates about 15 times per second, is possibly the remnant from this event. If the supernova and pulsar are associated, the star is still rotating about as quickly as it did when it first formed. This is in contrast to the Crab pulsar, known to be the remnant of the SN 1054 supernova in the year 1054, which has lost two-thirds of its rotational energy in essentially the same time span. Recent radio surveys of 3C 58, however, indicate that this supernova remnant may be much older and thus not associated with SN 1181.

Transient astronomical event

A transient astronomical event, often shortened by astronomers to a transient, is an astronomical object or phenomenon whose duration may be from seconds to days, weeks, or even several years. This is in contrast to the timescale of the millions or billions of years during which the galaxies and their component stars in our universe have evolved. Singularly, the term is used for violent deep-sky events, such as supernovae, novae, dwarf nova outbursts, gamma-ray bursts, and tidal disruption events, as well as gravitational microlensing, transits and eclipses. These events are part of the broader topic of time domain astronomy.

Westerlund 1

Westerlund 1 (abbreviated Wd1, sometimes called Ara Cluster) is a compact young super star cluster in the Milky Way galaxy, about 3.5–5 kpc away from Earth. It is one of the most massive young star clusters in the Milky Way, and was discovered by Bengt Westerlund in 1961 but remained largely unstudied for many years due to high interstellar absorption in its direction. In the future, it will probably evolve into a globular cluster.The cluster contains a large number of rare, evolved, high-mass stars, including: 6 yellow hypergiants, 4 red supergiants including Westerlund 1-26, one of the largest known stars, 24 Wolf-Rayet stars, a luminous blue variable, many OB supergiants, and an unusual supergiant sgB[e] star which has been proposed to be the remnant of a recent stellar merger. In addition, X-ray observations have revealed the presence of the anomalous X-ray pulsar CXO J164710.2-455216, a slow rotating neutron star that must have formed from a high-mass progenitor star. Westerlund 1 is believed to have formed in a single burst of star formation, implying the constituent stars have similar ages and compositions.

Aside from hosting some of the most massive and least-understood stars in our galaxy, Westerlund 1 is useful as a relatively nearby, easy to observe super star cluster that can help astronomers determine what occurs within extragalactic super star clusters.

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.

X-ray star

X-ray star may refer to:

Be/X-ray binary, a class of high-mass X-ray binaries that consist of a Be star and a neutron star

X-ray binary, a class of binary stars that are luminous in X-rays

X-ray burster, a class of X-ray binary stars exhibiting periodic and rapid increases in luminosity that peak in the X-ray regime of the electromagnetic spectrum

X-ray pulsar, a class of astronomical objects that are X-ray sources displaying strict periodic variations in X-ray intensity

Single pulsars
Binary pulsars

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