Editing Millisecond pulsar (section)

== Pulsar rotational speed limits ==
[[File:The star cluster Terzan 5.jpg|thumb|The stellar grouping [[Terzan 5]]]]

The first millisecond pulsar, [[PSR B1937+21]], was discovered in 1982 by [[Don Backer|Backer]] ''et al''.<ref>{{Citation | last1 = Backer | first1 = D. C. | last2 = Kulkarni | first2 = S. R. | last3 = Heiles | first3 = C. | last4 = Davis | first4 = M. M. | last5 = Goss | first5 = W. M. | title = A millisecond pulsar | year = 1982 | journal = Nature | volume = 300 | issue = 5893 | pages = 615–618 | bibcode = 1982Natur.300..615B|doi = 10.1038/300615a0 | s2cid = 4247734 }}</ref> Spinning roughly 641 times per second, it remains the second fastest-spinning millisecond pulsar of the approximately 200 that have been discovered.<ref name="atnf_list">{{cite web | title = The ATNF Pulsar Database | url= http://www.atnf.csiro.au/research/pulsar/psrcat/proc_form.php?Name=Name&P0=P0&P1=P1&startUserDefined=true&c1_val=&c2_val=&c3_val=&c4_val=&sort_attr=p0&sort_order=asc&condition=&pulsar_names=&ephemeris=short&coords_unit=raj%2Fdecj&radius=&coords_1=&coords_2=&style=Long+with+last+digit+error&no_value=*&fsize=3&x_axis=&x_scale=linear&y_axis=&y_scale=linear&state=query&table_bottom.x=74&table_bottom.y=20 | access-date = 2009-05-17}}</ref> Pulsar [[PSR J1748-2446ad]], discovered in 2004, is the fastest-spinning pulsar known, as of 2023, spinning 716 times per second.<ref>{{Cite journal |last1=Hessels |first1=Jason |last2=Ransom |first2=Scott M. |last3=Stairs |first3=Ingrid H. |last4=Freire |first4=Paulo C. C. |author5-link=Victoria Kaspi |last5=Kaspi |first5=Victoria M. |last6=Camilo |first6=Fernando |title=A Radio Pulsar Spinning at 716 Hz |journal=[[Science (journal)|Science]] |volume=311 |issue=5769 |pages=1901–1904 |year=2006 |doi=10.1126/science.1123430 |pmid=16410486 |bibcode=2006Sci...311.1901H|arxiv = astro-ph/0601337 |s2cid=14945340 }}</ref><ref>{{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
 | url-status = dead
 }}</ref>

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,<ref name="gr_recycling">{{cite journal |author1=Cook, G. B. |author2=Shapiro, S. L. |author3=Teukolsky, S. A. | title = Recycling Pulsars to Millisecond Periods in General Relativity | journal = Astrophysical Journal Letters | volume = 423 | pages = 117–120 | year = 1994 | bibcode = 1994ApJ...423L.117C | doi = 10.1086/187250}}</ref><ref name="minimum_period">{{cite journal |author1=Haensel, P. |author2=Lasota, J. P. |author3=Zdunik, J. L. | title = On the minimum period of uniformly rotating neutron stars | journal = Astronomy and Astrophysics | volume = 344 | pages = 151–153 | year = 1999 | bibcode = 1999A&A...344..151H}}</ref> 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.<ref name="chakrabarty">{{cite journal |author1=Chakrabarty, D. |author2=Morgan, E. H. |author3=Muno, M. P. |author4=Galloway, D. K. |author5=Wijnands, R. |author6=van der Klis, M. |author7=Markwardt, C. B. | title = Nuclear-powered millisecond pulsars and the maximum spin frequency of neutron stars | journal = Nature | volume = 424 | issue = 6944 | pages = 42–44 | year = 2003 | doi = 10.1038/nature01732 | pmid = 12840751|arxiv = astro-ph/0307029 |bibcode = 2003Natur.424...42C |s2cid=1938122 }}</ref>

In early 2007 data from the [[Rossi X-ray Timing Explorer]] and [[INTEGRAL]] spacecraft discovered a neutron star [[XTE J1739-285]] rotating at 1122&nbsp;Hz.<ref>{{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
 }}</ref> The result is not statistically significant, with a significance level of only 3 [[normal distribution|sigma]]. While it is an interesting candidate for further observations, current results are inconclusive.  Still, it is believed that gravitational radiation plays a role in slowing the rate of rotation. One [[X-ray pulsar]] that spins at 599 revolutions per second, [[IGR J00291+5934]], is a prime candidate for helping detect such waves in the future (most such X-ray pulsars only spin at around 300 rotations per second).

Millisecond pulsars, which can be timed with high precision, have a stability comparable to [[atomic clock|atomic-clock]]-based time standards when averaged over decades.<ref name=Matsakis1997>{{cite journal | author = Matsakis, D. N. | author2 = Taylor, J. H. | author3 = Eubanks, T. M. | url = http://aa.springer.de/papers/7326003/2300924.pdf | title = A Statistic for Describing Pulsar and Clock Stabilities | journal = Astronomy and Astrophysics | volume = 326 | date = 1997 | pages = 924–928 | access-date = 2010-04-03 | bibcode = 1997A&A...326..924M | archive-date = 2011-07-25 | archive-url = https://web.archive.org/web/20110725022625/http://aa.springer.de/papers/7326003/2300924.pdf | url-status = dead }}</ref><ref>{{Cite journal|last1=Hartnett|first1=John G.|last2=Luiten|first2=Andre N.|date=2011-01-07|title=Colloquium: Comparison of astrophysical and terrestrial frequency standards|journal=Reviews of Modern Physics|volume=83|issue=1|pages=1–9|doi=10.1103/revmodphys.83.1|arxiv=1004.0115|bibcode=2011RvMP...83....1H|s2cid=118396798|issn=0034-6861}}</ref> This also makes them very sensitive probes of their environments. For example, anything placed in orbit around them causes periodic [[Doppler effect|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 [[Extrasolar planet|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.<ref>{{Cite news |last=Rasio|first=Frederic|year=2011 |title=Planet Discovery near Pulsars |periodical=[[Science (journal)|Science]] |doi=10.1126/science.1212489 |url=https://www.science.org/doi/full/10.1126/science.1212489 }}</ref>