Millisecond pulsar

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Pulsar with a rotational period less than about 10 milliseconds

title: "Millisecond pulsar" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["pulsars", "millisecond-pulsars"] description: "Pulsar with a rotational period less than about 10 milliseconds" topic_path: "general/pulsars" source: "https://en.wikipedia.org/wiki/Millisecond_pulsar" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Pulsar with a rotational period less than about 10 milliseconds ::

::figure[src="https://upload.wikimedia.org/wikipedia/commons/a/ab/Millisecond_Pulsar.jpg" caption="This diagram shows the steps astronomers say are needed to create a pulsar with a superfast spin. 1. A massive supergiant star and a "normal" Sun-like star orbit each other. 2. The massive star explodes, leaving a pulsar that eventually slows down, turns off, and becomes a cooling neutron star. 3. The Sun-like star eventually expands, spilling material on to the neutron star. This "accretion" speeds up the neutron star's spin. 4. Accretion ends, the neutron star is "recycled" into a millisecond pulsar. But in a densely packed globular cluster (2b)... The lowest mass stars are ejected, the remaining normal stars evolve, and the "recycling" scenario (3-4) takes place, creating many millisecond pulsars."] ::

A millisecond pulsar (MSP) is a pulsar with a rotational period less than about 10 milliseconds. Millisecond pulsars have been detected in radio, X-ray, and gamma ray portions of the electromagnetic spectrum. The leading hypothesis for the origin of millisecond pulsars is that they are old, rapidly rotating neutron stars that have been spun up or "recycled" through accretion of matter from a companion star in a close binary system.{{cite journal | last1 = Bisnovatyi-Kogan | first1 = G. S. | last2 = Komberg | first2 = B. V. | year = 1974 | title = Pulsars and close binary systems | journal = Soviet Astronomy | volume = 18 | page = 217 | url = https://ui.adsabs.harvard.edu/abs/1974SvA....18..217B | access-date = | bibcode = 1974SvA....18..217B

Origins

Millisecond pulsars are thought to be related to low-mass X-ray binary systems. It is thought that the X-rays in these systems are emitted by the accretion disk of a neutron star produced by the outer layers of a companion star that has overflowed its Roche lobe. The transfer of angular momentum from this accretion event can increase the rotation rate of the pulsar to hundreds of times per second, as is observed in millisecond pulsars.

There has been recent evidence that the standard evolutionary model fails to explain the evolution of all millisecond pulsars, especially young millisecond pulsars with relatively high magnetic fields, e.g. PSR B1937+21. Bülent Kiziltan and S. E. Thorsett (UCSC) showed that different millisecond pulsars must form by at least two distinct processes. But the nature of the other process remains a mystery.

Many millisecond pulsars are found in globular clusters. This is consistent with the spin-up hypothesis of their formation, as the extremely high stellar density of these clusters implies a much higher likelihood of a pulsar having (or capturing) a giant companion star. Currently there are approximately 130 millisecond pulsars known in globular clusters.{{cite web | last = Freire | first = Paulo | title = Pulsars in globular clusters | publisher = Arecibo Observatory | url = http://www2.naic.edu/~pfreire/GCpsr.html | access-date =2007-01-18 }} The globular cluster Terzan 5 contains 37 of these, followed by 47 Tucanae with 22 and M28 and M15 with 8 pulsars each.

Pulsar rotational speed limits

::figure[src="https://upload.wikimedia.org/wikipedia/commons/4/47/The_star_cluster_Terzan_5_(eso0945a).jpg" caption="The stellar grouping [[Terzan 5"] ::

The first millisecond pulsar, PSR B1937+21, was discovered in 1982 by Backer et al. Spinning roughly 641 times per second, it remains the second fastest-spinning millisecond pulsar of the approximately 200 that have been discovered. Pulsar PSR J1748-2446ad, discovered in 2004, is the fastest-spinning pulsar known, as of 2025, spinning 716 times per second.{{Cite news | last = Naeye | first = Robert | date = 2006-01-13 | title = Spinning Pulsar Smashes Record | periodical = Sky & Telescope | url = http://www.skyandtelescope.com/news/3311021.html?page=1&c=y | access-date = 2008-01-18 | archive-url = https://web.archive.org/web/20071229113749/http://www.skyandtelescope.com/news/3311021.html?page=1&c=y | archive-date = 2007-12-29

Current models of neutron star structure and evolution predict that pulsars would break apart if they spun at a rate of c. 1500 rotations per second or more, and that at a rate of above about 1000 rotations per second they would lose energy by gravitational radiation faster than the accretion process would accelerate them.

In early 2007 data from the Rossi X-ray Timing Explorer and INTEGRAL spacecraft discovered a neutron star XTE J1739-285 rotating at 1122 Hz.{{Cite journal | title = Integral points to the fastest spinning neutron star | journal = Spaceflight Now | publisher = European Space Agency | date = 2007-02-19 | url = http://www.spaceflightnow.com/news/n0702/19neutronstar/ | access-date = 2007-02-20 |bibcode=2009ApJ...693L.109K |arxiv = 0902.0604 |doi = 10.1088/0004-637X/693/2/L109 | last1 = Kiziltan | first1 = Bulent | last2 = Thorsett | first2 = Stephen E. | volume = 693 | issue = 2 | s2cid = 2156395

Millisecond pulsars, which can be timed with high precision, have a stability comparable to atomic-clock-based time standards when averaged over decades. This also makes them very sensitive probes of their environments. For example, anything placed in orbit around them causes periodic Doppler shifts in their pulses' arrival times on Earth, which can then be analyzed to reveal the presence of the companion and, with enough data, provide precise measurements of the orbit and the object's mass. The technique is so sensitive that even objects as small as asteroids can be detected if they happen to orbit a millisecond pulsar. The first confirmed exoplanets, discovered several years before the first detections of exoplanets around "normal" solar-like stars, were found in orbit around a millisecond pulsar, PSR B1257+12. These planets remained, for many years, the only Earth-mass objects known outside of the Solar System. One of them, PSR B1257+12 b, has an even smaller mass, just under twice that of the Moon, and is still today the smallest-mass object known beyond the Solar System.

Gravitational wave detection using pulsar timing

Main article: Pulsar timing array

Gravitational waves are an important prediction from Einstein's general theory of relativity and result from the bulk motion of matter, fluctuations during the early universe and the dynamics of space-time itself. Pulsars are rapidly rotating, highly magnetized neutron stars formed during the supernova explosions of massive stars. They act as highly accurate clocks with a wealth of physical applications ranging from celestial mechanics, neutron star seismology, tests of strong-field gravity and Galactic astronomy.

The proposal to use pulsars as gravitational wave detectors was originally made by Sazhin | last=Sazhin | first=M.V. | date=1978 | title=Opportunities for detecting ultralong gravitational waves | journal=Sov. Astron. | volume=22 | pages=36–38 |bibcode = 1978SvA....22...36S }} and Detweiler | last=Detweiler | first=S.L. | date=1979 | title=Pulsar timing measurements and the search for gravitational waves | journal=Astrophysical Journal | volume=234 | pages=1100–1104 | bibcode = 1979ApJ...234.1100D | doi = 10.1086/157593

::figure[src="https://upload.wikimedia.org/wikipedia/commons/6/64/correlation_vs_angular_separation_between_pulsars.svg" caption="website=Berkeley}}"] ::

Hellings and Downs | author=Hellings, R.W. | author2=Downs, G.S. | date=1983 | title=Upper limits on the isotropic gravitational radiation background from pulsar timing analysis | journal=Astrophysical Journal Letters | volume=265 | pages=L39–L42 | bibcode = 1983ApJ...265L..39H |doi = 10.1086/183954 | doi-access=free | author=Foster, R.S. | author2=Backer, D.C. | date=1990 | title=Constructing a pulsar timing array | journal=Astrophysical Journal | volume=361 | pages=300–308 | doi = 10.1086/169195 | bibcode = 1990ApJ...361..300F

The advent of digital data acquisition systems, new radio telescopes and receiver systems, and the discoveries of many new millisecond pulsars advanced the sensitivity of the pulsar timing array to gravitational waves in the early stages of the international effort. | author=Hobbs, G. | display-authors=etal | date=2010 | title=The International Pulsar Timing Array project: using pulsars as a gravitational wave detector | journal=Classical and Quantum Gravity | volume=27 | issue = 8 | article-number=084013 | doi = 10.1088/0264-9381/27/8/084013 |bibcode = 2010CQGra..27h4013H |arxiv = 0911.5206 | s2cid=56073764 | author=Demorest, P. | display-authors=etal | date=2013 | title=Limits on the Stochastic Gravitational Wave Background from the North American Nanohertz Observatory for Gravitational Waves | journal=Astrophysical Journal | volume=762 | issue = 2 | pages=94–118 | doi = 10.1088/0004-637X/762/2/94 |bibcode = 2013ApJ...762...94D |arxiv = 1201.6641 | s2cid=13883914

In 2020, the collaboration presented the 12.5-year data release, which included strong evidence for a power-law stochastic process with common strain amplitude and spectral index across all pulsars, but statistically inconclusive data for the critical Hellings-Downs quadrupolar spatial correlation.

In June 2023, NANOGrav published its 15-year data release, at the same time as the European Pulsar Timing Array and the Indian Pulsar Timing Array's combined data set, the Parkes Pulsar Timing Array's third data release, and the first data release from the Chinese Pulsar Timing Array. These data releases presented the first evidence for a stochastic gravitational wave background. In particular, it included the first measurements of the Hellings-Downs curve, the tell-tale sign of the gravitational wave origin of the observations. The MeerKAT Pulsar Timing Array published further evidence for the Hellings-Downs curve in December 2024.

References

References

  1. (1991). "Formation and evolution of binary and millisecond radio pulsars". Physics Reports.
  2. (2006). "Formation and evolution of compact stellar X-ray sources".
  3. (2009). "Constraints on Pulsar Evolution: The Joint Period-Spin-down Distribution of Millisecond Pulsars".
  4. Naeye, Robert. (2009). "Surprising Trove of Gamma-Ray Pulsars".
  5. (1982). "A millisecond pulsar". Nature.
  6. "The ATNF Pulsar Database".
  7. (2006). "A Radio Pulsar Spinning at 716 Hz". [[Science (journal).
  8. (1994). "Recycling Pulsars to Millisecond Periods in General Relativity". Astrophysical Journal Letters.
  9. (1999). "On the minimum period of uniformly rotating neutron stars". Astronomy and Astrophysics.
  10. (2003). "Nuclear-powered millisecond pulsars and the maximum spin frequency of neutron stars". Nature.
  11. Matsakis, D. N.. (1997). "A Statistic for Describing Pulsar and Clock Stabilities". Astronomy and Astrophysics.
  12. (2011-01-07). "Colloquium: Comparison of astrophysical and terrestrial frequency standards". Reviews of Modern Physics.
  13. Rasio, Frederic. (2011). "Planet Discovery near Pulsars".
  14. "ShieldSquare Captcha".
  15. (August 11, 2022). "After 15 years, pulsar timing yields evidence of cosmic gravitational wave background".
  16. (2020-12-01). "The NANOGrav 12.5 yr Data Set: Search for an Isotropic Stochastic Gravitational-wave Background". The Astrophysical Journal.
  17. (11 January 2021). "Gravitational Wave Search Finds Tantalizing New Clue". [[NASA]].
  18. "Hellings and Downs curve".
  19. (2023-07-01). "The NANOGrav 15 yr Data Set: Evidence for a Gravitational-wave Background". The Astrophysical Journal Letters.
  20. NANOGrav Collaboration. (29 June 2023). "Focus on NANOGrav's 15 yr Data Set and the Gravitational Wave Background". The Astrophysical Journal Letters.
  21. (3 October 2023). "The second data release from the European Pulsar Timing Array: III. Search for gravitational wave signals". Astronomy and Astrophysics.
  22. (29 June 2023). "Search for an Isotropic Gravitational-wave Background with the Parkes Pulsar Timing Array". The Astrophysical Journal Letters.
  23. (1 July 2023). "Searching for the Nano-Hertz Stochastic Gravitational Wave Background with the Chinese Pulsar Timing Array Data Release I". Research in Astronomy and Astrophysics.
  24. (11 January 2025). "The MeerKAT Pulsar Timing Array: the first search for gravitational waves with the MeerKAT radio telescope". Monthly Notices of the Royal Astronomical Society.

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