Editing White dwarf (section)

=== Stars with very low mass ===
If the mass of a main-sequence star is lower than approximately half a [[solar mass]], it will never become hot enough to ignite and fuse helium in its core.<ref name=Brown2011>{{cite journal |first1=J. M. |last1=Brown |first2=M. |last2=Kilic |first3=W. R. |last3=Brown |first4=S. J. |last4=Kenyon |date=2011 |title=The binary fraction of low-mass white dwarfs |journal=The Astrophysical Journal |volume=730 |number=67 |page=67 |doi=10.1088/0004-637X/730/2/67|arxiv=1101.5169 |bibcode=2011ApJ...730...67B }}</ref> It is thought that, over a lifespan that considerably exceeds the age of the universe ({{circa}} 13.8&nbsp;billion years),<ref name=aou>
{{cite journal
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</ref> such a star will eventually burn all its hydrogen, for a while becoming a [[Blue dwarf (red-dwarf stage)|blue dwarf]], and end its evolution as a helium white dwarf composed chiefly of [[helium-4]] nuclei.<ref>
{{cite journal
 |last1=Laughlin |first1=G.
 |last2=Bodenheimer |first2=P.
 |last3=Adams |first3=Fred C.
 |date=1997
 |title=The End of the Main Sequence
 |journal=The Astrophysical Journal
 |volume=482 |issue=1
 |pages=420–432
 |bibcode=1997ApJ...482..420L
 |doi=10.1086/304125
 |doi-access=free
}}</ref> Due to the very long time this process takes, it is not thought to be the origin of the observed helium white dwarfs. Rather, they are thought to be mostly the product of mass loss in binary systems.<ref name="rln" /><ref name="apj606_L147" /><ref name="he2" /><ref name="sj">{{cite web |url=http://star.arm.ac.uk/~csj/pus/astnow/astnow.html |title=Stars Beyond Maturity |archive-url=https://web.archive.org/web/20150404004046/http://star.arm.ac.uk/~csj/pus/astnow/astnow.html |archive-date=4 April 2015 |author=Jeffery, Simon |access-date=3 May 2007}}</ref><ref>
{{cite journal
 |last1=Sarna |first1=M. J.
 |last2=Ergma |first2=E.
 |last3=Gerškevitš |first3=J.
 |journal=Astronomische Nachrichten
 |date=2001
 |title=Helium core white dwarf evolution – including white dwarf companions to neutron stars
 |volume=322 |issue=5–6 |pages=405–410
 |bibcode=2001AN....322..405S
 |doi= 10.1002/1521-3994(200112)322:5/6<405::AID-ASNA405>3.0.CO;2-6
}}</ref><ref>
{{cite journal
 |last1=Benvenuto |first1=O. G.
 |last2=De Vito |first2=M. A.
 |date=2005
 |title=The formation of helium white dwarfs in close binary systems – II
 |journal=Monthly Notices of the Royal Astronomical Society
 |volume=362 |issue=3 |pages=891–905
 |bibcode=2005MNRAS.362..891B
 |doi= 10.1111/j.1365-2966.2005.09315.x |doi-access=free
}}</ref> Proposals to explain those helium white dwarfs that are not part of binary systems include mass loss due to a large planetary companion, stars being stripped of material by companions exploding as supernovae, and various types of stellar mergers.<ref>
{{cite journal
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 |last2=Tauris |first2=T. M.
 |title=Formation of undermassive single white dwarfs and the influence of planets on late stellar evolution
 |date=1998
 |journal=Astronomy and Astrophysics
 |volume=335 |pages=L85
 |arxiv= astro-ph/9806011
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}}</ref><ref>
{{cite journal
 |first1=Xianfei |last1=Zhang
 |first2=Philip D. |last2=Hall
 |first3=C. Simon |last3=Jeffery
 |first4=Shaolan |last4=Bi
 |year=2018
 |title=Evolution models of helium white dwarf–main-sequence star merger remnants: the mass distribution of single low-mass white dwarfs
 |journal=Monthly Notices of the Royal Astronomical Society
 |volume=474
 |pages=427–432
 |doi=10.1093/mnras/stx2747
 |doi-access=free
 |arxiv=1711.03285
}}</ref>