Editing White dwarf (section)

=== Magnetic field ===
Magnetic fields in white dwarfs with a strength at the surface of {{circa}} 1&nbsp;million [[Gauss (unit)|gauss]] (100&nbsp;[[tesla (unit)|teslas]]) were predicted by [[P. M. S. Blackett]] in 1947 as a consequence of a physical law he had proposed, which stated that an uncharged, rotating body should generate a magnetic field proportional to its [[angular momentum]].<ref>
{{cite journal
 |last1=Blackett |first1=P. M. S.
 |date=1947
 |title=The Magnetic Field of Massive Rotating Bodies
 |journal=Nature
 |volume=159 |issue=4046 |pages=658–66
 |bibcode=1947Natur.159..658B
 |doi= 10.1038/159658a0
 |pmid=20239729
 |s2cid=4133416
}}</ref> This putative law, sometimes called the ''[[Blackett effect]]'', was never generally accepted, and by the 1950s even Blackett felt it had been refuted.<ref>
{{cite journal
 |last1=Lovell |first1=B.
 |date=1975
 |title=Patrick Maynard Stuart Blackett, Baron Blackett, of Chelsea. 18 November 1897 – 13 July 1974
 |journal=Biographical Memoirs of Fellows of the Royal Society
 |volume=21 |pages=1–115
 |doi=10.1098/rsbm.1975.0001
 |jstor=769678
 |s2cid=74674634
}}</ref>{{rp|page=39–43}} In the 1960s, it was proposed that white dwarfs might have magnetic fields due to conservation of total surface [[magnetic flux]] that existed in its progenitor star phase.<ref>
{{cite journal
 |last1=Landstreet |first1=John D.
 |date=1967
 |title=Synchrotron radiation of neutrinos and its astrophysical significance
 |journal=Physical Review
 |volume=153 |issue=5 |pages=1372–1377
 |bibcode=1967PhRv..153.1372L
 |doi= 10.1103/PhysRev.153.1372
}}</ref> A surface magnetic field of {{circa}} 100&nbsp;gauss (0.01&nbsp;T) in the progenitor star would thus become a surface magnetic field of {{circa}} 100&nbsp;×&nbsp;100<sup>2</sup>&nbsp;= 1&nbsp;million gauss (100&nbsp;T) once the star's radius had shrunk by a factor of 100.<ref name="physrev" />{{rp|§8}}<ref>
{{cite journal
 |last1=Ginzburg |first1=V. L.
 |last2=Zheleznyakov |first2=V. V.
 |last3=Zaitsev |first3=V. V.
 |date=1969
 |title=Coherent mechanisms of radio emission and magnetic models of pulsars
 |journal=Astrophysics and Space Science
 |volume=4 |issue=4 |pages=464–504
 |bibcode=1969Ap&SS...4..464G
 |doi= 10.1007/BF00651351
 |s2cid=119003761
}}</ref>{{rp|page=484}} The first magnetic white dwarf to be discovered was [[GJ 742]] (also known as {{nowrap|GRW +70 8247}}), which was identified by James Kemp, John Swedlund, John Landstreet and [[Roger Angel]] in 1970 to host a magnetic field by its emission of [[circularly polarized]] light.<ref>
{{cite journal
 |last1=Kemp       |first1=J.C.    |last2=Swedlund |first2=J.B.
 |last3=Landstreet |first3=J.D.    |last4=Angel    |first4=J.R.P.
 |date=1970
 |title=Discovery of circularly polarized light from a white dwarf
 |journal=[[The Astrophysical Journal]]
 |volume=161 |page=L77
 |bibcode=1970ApJ...161L..77K
 |doi=10.1086/180574  |doi-access=free
}}
</ref> It is thought to have a surface field of approximately 300&nbsp;million gauss (30&nbsp;kT).<ref name="physrev" />{{rp|§8}}

Since 1970, magnetic fields have been discovered in well over 200&nbsp;white dwarfs, ranging from {{val|2|e=3}} to {{val|e=9}}&nbsp;gauss (0.2&nbsp;T to 100&nbsp;kT).<ref>
{{cite journal
 |last1=Ferrario |first1=Lilia
 |last2=de Martino |first2=Domtilla
 |last3=Gaensicke |first3=Boris
 |date=2015
 |title=Magnetic white dwarfs
 |journal=[[Space Science Reviews]]
 |volume=191 |issue=1–4 |pages=111–169
 |bibcode=2015SSRv..191..111F
 |doi= 10.1007/s11214-015-0152-0  |arxiv=1504.08072|s2cid=119057870
}}
</ref> Many of the presently known magnetic white dwarfs are identified by low-resolution spectroscopy, which is able to reveal the presence of a magnetic field of 1&nbsp;megagauss or more. Thus the basic identification process also sometimes results in discovery of magnetic fields.<ref>
{{cite journal
 |last1=Kepler |first1=S.O.
 |last2=Pelisoli |first2=I.
 |last3=Jordan |first3=S.
 |last4=Kleinman |first4=S.J.
 |last5=Koester |first5=D.
 |last6=Kuelebi |first6=B.
 |last7=Pecanha |first7=V.
 |last8=Castanhiera |first8=B.G.
 |last9=Nitta |first9=A.
 |last10=Costa |first10=J.E.S.
 |last11=Winget |first11=D.E.
 |last12=Kanaan |first12=A.
 |last13=Fraga |first13=L.
 |date=2013
 |title=Magnetic white dwarf stars in the Sloan Digital Sky Survey
 |journal=Monthly Notices of the Royal Astronomical Society
 |volume=429 |issue=4 |pages=2934–2944
 |bibcode=2013MNRAS.429.2934K
 |doi= 10.1093/mnras/sts522
 |doi-access=free
 |arxiv=1211.5709|s2cid=53316287
}}
</ref> White dwarf magnetic fields may also be measured without spectral lines, using the techniques of broadband circular [[polarimetry]], or maybe through measurement of their frequencies of radio emission via the [[Solar radio emission#Electron-cyclotron maser emission|electron cyclotron maser]].<ref name=Route2024/>  It has been estimated that at least 10% of white dwarfs have fields in excess of 1&nbsp;million gauss (100&nbsp;T).<ref>
{{cite journal
 |last1=Landstreet |first1=J.D.
 |last2=Bagnulo |first2=S.
 |last3=Valyavin |first3=G.G.
 |last4=Fossati |first4=L.
 |last5=Jordan |first5=S.
 |last6=Monin |first6=D.
 |last7=Wade |first7=G.A.
 |date=2012
 |title=On the incidence of weak magnetic fields in DA white dwarfs
 |journal=Astronomy and Astrophysics
 |volume=545 |issue=A30 |pages=9pp
 |bibcode=2012A&A...545A..30L |doi=10.1051/0004-6361/201219829
 |arxiv=1208.3650|s2cid=55153825
}}
</ref><ref>
{{cite journal
 |last1=Liebert |first1=James
 |last2=Bergeron |first2=P.
 |last3=Holberg |first3=J. B.
 |title=The True Incidence of Magnetism Among Field White Dwarfs
 |date=2003
 |journal=The Astronomical Journal
 |volume=125 |issue=1 |pages=348–353
 |arxiv=astro-ph/0210319  |bibcode=2003AJ....125..348L
 |doi=10.1086/345573   |s2cid=9005227
}}</ref> The magnetic fields in a white dwarf may allow for the existence of a new type of [[chemical bond]], [[perpendicular paramagnetic bond]]ing, in addition to [[ionic bond|ionic]] and [[covalent bond]]s, though detecting molecules bonded in this way is expected to be difficult.<ref>
{{cite news
 |first=Zeeya  |last=Merali
 |date=19 July 2012
 |title=Stars draw atoms closer together
 |department=Nature News & Comment
 |journal=[[Nature (journal)|Nature]]
 |doi=10.1038/nature.2012.11045  |doi-access=free
 |url=http://www.nature.com/news/stars-draw-atoms-closer-together-1.11045
 |access-date=21 July 2012  |url-status=live 
 |archive-url=https://web.archive.org/web/20120720200709/http://www.nature.com/news/stars-draw-atoms-closer-together-1.11045
 |archive-date=20 July 2012
}}
</ref>

The highly magnetized white dwarf in the binary system [[AR Scorpii]] was identified in 2016 as the first [[pulsar]] in which the compact object is a white dwarf instead of a neutron star.<ref>
{{cite journal
 |last1=Buckley  |first1=D.A.H.    |last2=Meintjes |first2=P.J.
 |last3=Potter   |first3=S.B.      |last4=Marsh    |first4=T.R.
 |last5=Gänsicke |first5=B.T.
 |date=2017-01-23
 |title=Polarimetric evidence of a white dwarf pulsar in the binary system AR Scorpii  |language=en
 |journal=[[Nature Astronomy]]
 |volume=1  |issue=2  |page=0029
 |doi=10.1038/s41550-016-0029  |s2cid=15683792 
 |arxiv=1612.03185  |bibcode=2017NatAs...1E..29B
}}
</ref> A second white dwarf pulsar was discovered in 2023.<ref>{{cite journal|first1=Ingrid |last1=Pelisoli |display-authors=etal |title=A 5.3-min-period pulsing white dwarf in a binary detected from radio to X-rays |journal=Nature Astronomy |volume=7 |pages=931–942 |year=2023 |issue=8 |doi=10.1038/s41550-023-01995-x |arxiv=2306.09272|bibcode=2023NatAs...7..931P }}</ref>