Editing Neutron star (section)

==History of discoveries==
[[File:Isolated Neutron Star RX J185635-3754 - opo9732a.jpg|thumb|left|The first direct observation of an isolated neutron star in visible light. The neutron star is RX J1856.5−3754.]]

At the meeting of the [[American Physical Society]] in December 1933 (the proceedings were published in January 1934), [[Walter Baade]] and [[Fritz Zwicky]] proposed the existence of neutron stars,<ref>{{cite journal |journal=Physical Review |volume=46 |title=Remarks on Super-Novae and Cosmic Rays |issue=1 |last1=Baade |first1=Walter |author-link=Walter Baade |last2=Zwicky |first2=Fritz |author-link2=Fritz Zwicky |name-list-style=amp |pages=76–77 |doi=10.1103/PhysRev.46.76.2 |date=1934 |bibcode=1934PhRv...46...76B |url=https://authors.library.caltech.edu/5999/1/BAApr34.pdf |access-date=2019-09-16 |archive-date=2021-02-24 |archive-url=https://web.archive.org/web/20210224205601/https://authors.library.caltech.edu/5999/1/BAApr34.pdf |url-status=live }}</ref>{{refn |group="lower-alpha" |Even before the discovery of neutron, in 1931, neutron stars were ''anticipated'' by [[Lev Landau]], who wrote about stars where "atomic nuclei come in close contact, forming one gigantic nucleus".<ref>{{cite journal |journal=Phys. Z. Sowjetunion |volume=1 |title=On the theory of stars |last=Landau |first=Lev D. |pages=285–288 |date=1932 }}</ref> However, the widespread opinion that Landau ''predicted'' neutron stars proves to be wrong.<ref>{{Cite book |bibcode = 2007ASSL..326.....H|title = Neutron Stars 1 : Equation of State and Structure|series= Astrophysics and Space Science Library|volume = 326|editor-last1 = Haensel|editor-first1 = P|editor-last2 = Potekhin|editor-first2 = A. Y|editor-last3 = Yakovlev|editor-first3 = D. G|year = 2007 |isbn=978-0387335438 |publisher=Springer |author=<!--Deny Citation Bot -->}}</ref>}} less than two years after [[Discovery of the neutron|the discovery of the neutron]] by [[James Chadwick]].<ref>{{cite journal
 | journal=Nature | volume=129
 | issue=3252 | pages=312
 | title=On the possible existence of a neutron
 | first=James | last=Chadwick
 | doi=10.1038/129312a0 | date=1932 |bibcode = 1932Natur.129Q.312C | s2cid=4076465
 | doi-access=free }}</ref> In seeking an explanation for the origin of a [[supernova]], they tentatively proposed that in supernova explosions ordinary stars are turned into stars that consist of extremely closely packed neutrons that they called neutron stars. Baade and Zwicky correctly proposed at that time that the release of the gravitational binding energy of the neutron stars powers the supernova: "In the supernova process, mass in bulk is annihilated". Neutron stars were thought to be too faint to be detectable and little work was done on them until November 1967, when [[Franco Pacini]] pointed out that if the neutron stars were spinning and had large magnetic fields, then electromagnetic waves would be emitted. Unknown to him, radio astronomer [[Antony Hewish]] and his graduate student [[Jocelyn Bell]] at Cambridge were shortly to detect radio pulses from stars that are now believed to be highly magnetized, rapidly spinning neutron stars, known as pulsars.

In 1965, Antony Hewish and [[Samuel Okoye]] discovered "an unusual source of high radio brightness temperature in the [[Crab Nebula]]".<ref>{{cite journal |journal=Nature |volume=207 |issue=4992 |pages=59–60 |title=Evidence of an unusual source of high radio brightness temperature in the Crab Nebula |last1=Hewish |first1=A. |last2=Okoye |first2=S. E. |name-list-style=amp |doi=10.1038/207059a0 |date=1965 |bibcode=1965Natur.207...59H |s2cid=123416790 }}</ref> This source turned out to be the Crab Pulsar that resulted from the great [[SN 1054|supernova of 1054]].

In 1967, [[Iosif Shklovsky]] examined the X-ray and optical observations of [[Scorpius X-1]] and correctly concluded that the radiation comes from a neutron star at the stage of [[accretion (astrophysics)|accretion]].<ref>{{Cite journal |last=Shklovsky |first=I. S. |title=On the Nature of the Source of X-Ray Emission of SCO XR-1 |journal=Astrophysical Journal |volume=148 |issue=1 |pages=L1–L4 |date=April 1967 |doi=10.1086/180001 |bibcode=1967ApJ...148L...1S }}</ref>

In 1967, Jocelyn Bell Burnell and Antony Hewish discovered regular radio pulses from [[PSR B1919+21]]. This pulsar was later interpreted as an isolated, rotating neutron star. The energy source of the pulsar is the rotational energy of the neutron star. The majority of known neutron stars (about 2000, as of 2010) have been discovered as pulsars, emitting regular radio pulses.

In 1968, [[Richard V. E. Lovelace]] and collaborators discovered period <math>P\!\approx 33</math> ms of the [[Crab pulsar]] using [[Arecibo Observatory]].<ref name="Lovelace1969">{{cite journal |bibcode=1969Natur.221..453C |title=Crab Nebula Pulsar NP 0532 |last1=Comella |first1=J. M. |last2=Craft |first2=H. D. |last3=Lovelace |first3=R. V. E. |last4=Sutton |first4=J. M. |journal=Nature |year=1969 |volume=221 |issue=5179 |page=453 |doi=10.1038/221453a0 |s2cid=4213758 }}</ref><ref name="Lovelace1969a">{{cite journal |bibcode=1969Natur.222..231L |title=Digital Search Methods for Pulsars |last1=Lovelace |first1=R. V. E. |last2=Sutton |first2=J. M. |journal=Nature |year=1969 |volume=222 |issue=5190 |page=231 |doi=10.1038/222231a0 |s2cid=4294389 }}</ref> After this discovery, scientists concluded that [[pulsars]] were rotating [[neutron stars]].<ref name="LovelaceTyler2012">{{cite journal |bibcode=2012Obs...132..186L |title=On the discovery of the period of the Crab Nebular pulsar |last1=Lovelace |first1=R. V. E. |last2=Tyler |first2=G. L. |journal=The Observatory |year=2012 |volume=132 |issue=3 |page=186 }}</ref> Before that, many scientists believed that pulsars were pulsating [[white dwarfs]].

In 1971, [[Riccardo Giacconi]], Herbert Gursky, Ed Kellogg, R. Levinson, E. Schreier, and H. Tananbaum discovered 4.8 second pulsations in an X-ray source in the [[constellation]] [[Centaurus]], [[Centaurus X-3|Cen X-3]].<ref>{{cite book |title=Rotation and Accretion Powered Pulsars |edition=illustrated |first1=Pranab |last1=Ghosh |publisher=World Scientific |year=2007 |isbn=978-981-02-4744-7 |page=8 |url=https://books.google.com/books?id=fmtqDQAAQBAJ&pg=PA8 |access-date=2016-11-29 |archive-date=2021-02-06 |archive-url=https://web.archive.org/web/20210206222506/https://books.google.com/books?id=fmtqDQAAQBAJ&pg=PA8 |url-status=live }}</ref> They interpreted this as resulting from a rotating hot neutron star. The energy source is gravitational and results from a [[Accretion (astrophysics)|rain of gas falling]] onto the surface of the [[Accretion-powered pulsar|neutron star]] from a [[companion star]] or the [[interstellar medium]].

In 1974, [[Antony Hewish]] was awarded the [[Nobel Prize in Physics]] "for his decisive role in the discovery of pulsars" without [[Jocelyn Bell]] who shared in the discovery.<ref>{{cite book |title=A Companion to Astronomy and Astrophysics: Chronology and Glossary with Data Tables |edition=illustrated |first1=Kenneth |last1=Lang |publisher=Springer Science & Business Media |year=2007 |isbn=978-0-387-33367-0 |page=82 |url=https://books.google.com/books?id=aUjkKuaVIloC&pg=PA82 |access-date=2016-11-29 |archive-date=2021-02-06 |archive-url=https://web.archive.org/web/20210206223425/https://books.google.com/books?id=aUjkKuaVIloC&pg=PA82 |url-status=live }}</ref>

In 1974, [[Joseph Hooton Taylor Jr.|Joseph Taylor]] and [[Russell Hulse]] discovered the first binary pulsar, [[PSR B1913+16]], which consists of two neutron stars (one seen as a pulsar) orbiting around their center of mass. [[Albert Einstein]]'s [[general relativity|general theory of relativity]] predicts that massive objects in short binary orbits should emit [[gravitational wave]]s, and thus that their orbit should decay with time. This was indeed observed, precisely as general relativity predicts, and in 1993, Taylor and Hulse were awarded the [[Nobel Prize in Physics]] for this discovery.<ref>{{cite book |title=Neutron Stars 1: Equation of State and Structure |edition=illustrated |first1=Paweł |last1=Haensel |first2=Alexander Y. |last2=Potekhin |first3=Dmitry G. |last3=Yakovlev |publisher=Springer Science & Business Media |year=2007 |isbn=978-0-387-47301-7 |page=474 |url=https://books.google.com/books?id=fgj_TZ06niYC&pg=PA474 |access-date=2016-11-29 |archive-date=2021-02-06 |archive-url=https://web.archive.org/web/20210206223723/https://books.google.com/books?id=fgj_TZ06niYC&pg=PA474 |url-status=live }}</ref>

In 1982, [[Don Backer]] and colleagues discovered the first millisecond pulsar, [[PSR B1937+21]].<ref>{{cite book |title=Pulsar Astronomy |edition=illustrated |first1=Francis |last1=Graham-Smith |publisher=Cambridge University Press |year=2006 |isbn=978-0-521-83954-9 |page=11 |url=https://books.google.com/books?id=AK9N3zxL4ToC&pg=PA11 |access-date=2016-11-29 |archive-date=2021-02-06 |archive-url=https://web.archive.org/web/20210206223536/https://books.google.com/books?id=AK9N3zxL4ToC&pg=PA11 |url-status=live }}</ref> This object spins 642 times per second, a value that placed fundamental constraints on the mass and radius of neutron stars. Many millisecond pulsars were later discovered, but PSR B1937+21 remained the fastest-spinning known pulsar for 24 years, until [[PSR J1748-2446ad]] (which spins ~716 times a second) was discovered.

In 2003, [[Marta Burgay]] and colleagues discovered the first double neutron star system where both components are detectable as pulsars, [[PSR J0737−3039]].<ref>{{cite book |title=Rotation and Accretion Powered Pulsars |edition=illustrated |first1=Pranab |last1=Ghosh |publisher=World Scientific |year=2007 |isbn=978-981-02-4744-7 |page=281 |url=https://books.google.com/books?id=fmtqDQAAQBAJ&pg=PA281 |access-date=2016-11-29 |archive-date=2021-02-06 |archive-url=https://web.archive.org/web/20210206223426/https://books.google.com/books?id=fmtqDQAAQBAJ&pg=PA281 |url-status=live }}</ref> The discovery of this system allows a total of 5 different tests of general relativity, some of these with unprecedented precision.

In 2010, Paul Demorest and colleagues measured the mass of the millisecond pulsar [[PSR J1614−2230]] to be {{Solar mass|{{val|1.97|0.04}}}}, using [[Shapiro delay]].<ref>{{cite journal |doi=10.1038/nature09466 |last1=Demorest |first1=Paul B. |last2=Pennucci |first2=T. |last3=Ransom |first3=S. M. |last4=Roberts |first4=M. S. |last5=Hessels |first5=J. W. |title= A two-solar-mass neutron star measured using Shapiro delay |journal=Nature |volume=467 |issue=7319 |pages=1081–1083 |bibcode=2010Natur.467.1081D |year=2010 |pmid=20981094 |arxiv=1010.5788 |s2cid=205222609 }}</ref> This was substantially higher than any previously measured neutron star mass ({{Solar mass|1.67}}, see [[PSR J1903+0327]]), and places strong constraints on the interior composition of neutron stars.

In 2013, [[John Antoniadis]] and colleagues measured the mass of [[PSR J0348+0432]] to be {{Solar mass|{{val|2.01|0.04}}}}, using white dwarf spectroscopy.<ref>{{cite journal |doi=10.1126/science.1233232 |last1=Antoniadis |first1=John |title=A Massive Pulsar in a Compact Relativistic Binary |journal=Science |volume=340 |issue=6131 |bibcode=2013Sci...340..448A |date=2012 |arxiv=1304.6875 |pages=1233232 |pmid=23620056 |citeseerx=10.1.1.769.4180 |s2cid=15221098 }}</ref> This confirmed the existence of such massive stars using a different method. Furthermore, this allowed, for the first time, a test of [[general relativity]] using such a massive neutron star.

In August 2017, LIGO and Virgo made first detection of gravitational waves produced by colliding neutron stars ([[GW170817]]),<ref>{{cite web |url=https://www.ligo.caltech.edu/news/ligo20171016 |title=LIGO Detection of Colliding Neutron Stars Spawns Global Effort to Study the Rare Event |first=Kimberly M. |last=Burtnyk |date=16 October 2017 |access-date=17 November 2017 |archive-date=23 October 2017 |archive-url=https://web.archive.org/web/20171023230823/https://www.ligo.caltech.edu/news/ligo20171016 |url-status=live }}</ref> leading to further discoveries about neutron stars.

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 [[Neutron star merger|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 [[Galaxy|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.<ref name="EA-20181016">{{cite news |author=University of Maryland |title=All in the family: Kin of gravitational wave source discovered - New observations suggest that kilonovae -- immense cosmic explosions that produce silver, gold and platinum--may be more common than thought |url=https://www.eurekalert.org/pub_releases/2018-10/uom-ait101518.php |date=16 October 2018 |work=[[EurekAlert!]] |access-date=17 October 2018 |author-link=University of Maryland |archive-date=16 October 2018 |archive-url=https://web.archive.org/web/20181016142323/https://www.eurekalert.org/pub_releases/2018-10/uom-ait101518.php |url-status=live }}</ref><ref name="NC-20181016">{{cite journal |author=Troja, E.|display-authors=etal|title=A luminous blue kilonova and an off-axis jet from a compact binary merger at z = 0.1341 |date=16 October 2018 |journal=[[Nature Communications]] |volume=9 |pages=4089|number=4089 (2018) |doi=10.1038/s41467-018-06558-7 |pmid=30327476|pmc=6191439|bibcode=2018NatCo...9.4089T|arxiv=1806.10624}}</ref><ref name="NASA-20181016">{{cite news |last=Mohon |first=Lee |title=GRB 150101B: A Distant Cousin to GW170817 |url=https://www.nasa.gov/mission_pages/chandra/images/grb-150101b-a-distant-cousin-to-gw170817.html |date=16 October 2018 |work=[[NASA]] |access-date=17 October 2018 |archive-date=22 March 2019 |archive-url=https://web.archive.org/web/20190322010201/https://www.nasa.gov/mission_pages/chandra/images/grb-150101b-a-distant-cousin-to-gw170817.html |url-status=live }}</ref><ref name="SPC-20181017">{{cite web |last=Wall |first=Mike |title=Powerful Cosmic Flash Is Likely Another Neutron-Star Merger |url=https://www.space.com/42158-another-neutron-star-crash-detected.html |date=17 October 2018 |work=[[Space.com]] |access-date=17 October 2018 |archive-date=17 October 2018 |archive-url=https://web.archive.org/web/20181017144255/https://www.space.com/42158-another-neutron-star-crash-detected.html |url-status=live }}</ref>

In July 2019, astronomers reported that a new method to determine the [[Hubble constant]], and resolve the discrepancy of earlier methods, has been proposed based on the mergers of pairs of neutron stars, following the detection of the neutron star merger of GW170817.<ref name="EA-20190708">{{cite news |author=National Radio Astronomy Observatory |title=New method may resolve difficulty in measuring universe's expansion - Neutron star mergers can provide new 'cosmic ruler' |url=https://www.eurekalert.org/pub_releases/2019-07/nrao-nmm070819.php |date=8 July 2019 |work=[[EurekAlert!]] |access-date=8 July 2019 |author-link=National Radio Astronomy Observatory |archive-date=8 July 2019 |archive-url=https://web.archive.org/web/20190708195937/https://www.eurekalert.org/pub_releases/2019-07/nrao-nmm070819.php |url-status=live }}</ref><ref name="NRAO-20190708">{{cite news |last=Finley |first=Dave |title=New Method May Resolve Difficulty in Measuring Universe's Expansion |url=https://public.nrao.edu/news/new-method-measuring-universe-expansion/ |date=8 July 2019 |work=[[National Radio Astronomy Observatory]] |access-date=8 July 2019 |archive-date=8 July 2019 |archive-url=https://web.archive.org/web/20190708231326/https://public.nrao.edu/news/new-method-measuring-universe-expansion/ |url-status=live }}</ref> Their measurement of the Hubble constant is {{val|70.3|+5.3|-5.0}} (km/s)/Mpc.<ref name="NAT-20190708">{{cite journal |author=Hotokezaka, K. |display-authors=et al. |title=A Hubble constant measurement from superluminal motion of the jet in GW170817 |date=8 July 2019 |journal=[[Nature Astronomy]] |volume=3 |issue=10 |pages=940–944 |doi=10.1038/s41550-019-0820-1 |arxiv=1806.10596 |bibcode=2019NatAs...3..940H |s2cid=119547153 }}</ref>

A 2020 study by [[University of Southampton]] PhD student Fabian Gittins suggested that surface irregularities ("mountains") may only be fractions of a millimeter tall (about 0.000003% of the neutron star's diameter), hundreds of times smaller than previously predicted, a result bearing implications for the non-detection of gravitational waves from spinning neutron stars.<ref name=mt-ls>{{cite web |url=https://www.livescience.com/millimeter-tall-neutron-star-mountains.html |title=Neutron star 'mountains' are actually microscopic bumps less than a millimeter tall |last=Baker |first=Harry |date=21 July 2021 |publisher=[[Live Science]] |access-date=25 July 2021 |archive-date=25 July 2021 |archive-url=https://web.archive.org/web/20210725063709/https://www.livescience.com/millimeter-tall-neutron-star-mountains.html |url-status=live }}</ref><ref name=mt-syfy>{{cite web |url=https://www.syfy.com/syfywire/tallest-mountain-neutron-star-fraction-millimeter-tall |title=The tallest mountain on a neutron star may be a fraction of a millimeter tall |last=Plait |first=Phil |date=23 July 2021 |publisher=[[Syfy]] |access-date=25 July 2021 |archive-date=25 July 2021 |archive-url=https://web.archive.org/web/20210725045955/https://www.syfy.com/syfywire/tallest-mountain-neutron-star-fraction-millimeter-tall |url-status=live }}</ref><ref name=gittins>{{cite journal |last1=Gittins |first1=Fabian |last2=Andersson |first2=Nils |date=2021 |title=Modelling neutron star mountains in relativity |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=507 |number=stab2048 |pages=116–128 |doi=10.1093/mnras/stab2048 |doi-access=free |arxiv=2105.06493}}</ref>

Using the [[James Webb Space Telescope|JWST]], astronomers have identified a neutron star within the remnants of the [[Supernova 1987A]] [[stellar explosion]] after seeking to do so for 37 years, according to a 23 February 2024 ''[[Science (journal)|Science]]'' article. In a paradigm shift, new JWST data provides the elusive direct confirmation of neutron stars within supernova remnants as well as a deeper understanding of the processes at play within SN 1987A's remnants.<ref name="Fransson_20240223">{{cite journal | doi=10.1126/SCIENCE.ADJ5796 | title=Emission lines due to ionizing radiation from a compact object in the remnant of Supernova 1987A | date=2024 | last1=Fransson | first1=C. | last2=Barlow | first2=M. J. | last3=Kavanagh | first3=P. J. | last4=Larsson | first4=J. | last5=Jones | first5=O. C. | last6=Sargent | first6=B. | last7=Meixner | first7=M. | last8=Bouchet | first8=P. | last9=Temim | first9=T. | last10=Wright | first10=G. S. | last11=Blommaert | first11=J. A. D. L. | last12=Habel | first12=N. | last13=Hirschauer | first13=A. S. | last14=Hjorth | first14=J. | last15=Lenkić | first15=L. | last16=Tikkanen | first16=T. | last17=Wesson | first17=R. | last18=Coulais | first18=A. | last19=Fox | first19=O. D. | last20=Gastaud | first20=R. | last21=Glasse | first21=A. | last22=Jaspers | first22=J. | last23=Krause | first23=O. | last24=Lau | first24=R. M. | last25=Nayak | first25=O. | last26=Rest | first26=A. | last27=Colina | first27=L. | last28=Van Dishoeck | first28=E. F. | last29=Güdel | first29=M. | last30=Henning | first30=Th. | journal=Science | volume=383 | issue=6685 | pages=898–903 | arxiv=2403.04386 | bibcode=2024Sci...383..898F | display-authors=1 }}</ref>