Editing Black dwarf (section)

==Formation==
A white dwarf is what remains of a [[main sequence]] star of low or medium mass (below approximately 9 to 10&nbsp;solar masses ({{Solar mass|link=y}})) after it has either expelled or [[nuclear fusion|fused]] all the [[chemical element|element]]s for which it has sufficient temperature to fuse.<ref name="2003ApJ...591..288H" /> What is left is then a dense sphere of [[Degenerate matter#Electron degeneracy|electron-degenerate matter]] that cools slowly by [[thermal radiation]], eventually becoming a black dwarf.<ref name="on">{{cite web |url=http://www.astronomy.ohio-state.edu/~jaj/Ast162/lectures/notesWL22.pdf |title=Extreme Stars: White Dwarfs & Neutron Stars |first=Jennifer |last=Johnson |publisher=[[Ohio State University]] |access-date=2007-05-03 |df=dmy-all}}</ref><ref>{{cite web |last=Richmond |first=Michael |url=http://spiff.rit.edu/classes/phys230/lectures/planneb/planneb.html |title=Late stages of evolution for low-mass stars |publisher=Rochester Institute of Technology |access-date=2006-08-04 |df=dmy-all}}</ref> 

If black dwarfs were to exist, they would be challenging to detect because, by definition, they would emit very little [[radiation]]. They would, however, be detectable through their [[gravity|gravitational]] influence.<ref>{{cite journal |title=Baryonic Dark Matter: The Results from Microlensing Surveys |first1=Charles |last1=Alcock |first2=Robyn A. |last2=Allsman |first3=David |last3=Alves |first4=Tim S. |last4=Axelrod |first5=Andrew C. |last5=Becker |first6=David |last6=Bennett |first7=Kem H. |last7=Cook |first8=Andrew J. |last8=Drake |first9=Ken C. |last9=Freeman |first10=Kim |last10=Griest |first11=Matt |last11=Lehner |first12=Stuart |last12=Marshall |first13=Dante |last13=Minniti |first14=Bruce |last14=Peterson |first15= Mark |last15=Pratt |first16=Peter |last16=Quinn |first17=Alex |last17=Rodgers |first18=Chris |last18=Stubbs |first19=Will |last19=Sutherland |first20=Austin |last20=Tomaney |first21=Thor |last21=Vandehei |first22=Doug L. |last22=Welch |display-authors=6 |year=1999 |bibcode=1999ASPC..165..362A |volume=165 |page=362 |journal=In the Third Stromlo Symposium: The Galactic Halo}}</ref> Various [[White dwarf|white dwarfs]] cooled below {{convert|3900|K|C F}} (equivalent to M0 [[Stellar classification|spectral class]]) were found in 2012 by astronomers using [[MDM Observatory]]'s 2.4&nbsp;meter telescope. They are estimated to be 11 to 12&nbsp;billion years old.<ref name=2examples>{{cite web |url=http://www.spacedaily.com/reports/12_Billion_Year_Old_White_Dwarf_Stars_Only_100_Light_Years_Away_999.html |title=12&nbsp;Billion-year-old white-dwarf stars only 100&nbsp;light-years away |work=spacedaily.com |date=April 16, 2012 |place=Norman, Oklahoma |access-date=January 10, 2020 |df=dmy-all}}</ref>

Because the far-future evolution of stars depends on physical questions which are poorly understood, such as the nature of [[dark matter]] and the possibility and rate of [[proton decay]] (which is yet to be proven to exist), it is not known precisely how long it would take white dwarfs to cool to blackness.<ref name="Adams">{{Cite journal |title=A Dying Universe: The Long Term Fate and Evolution of Astrophysical Objects |journal=Reviews of Modern Physics |volume=69 |issue=2 |pages=337–372 |doi=10.1103/RevModPhys.69.337 |first1=Fred C. |last1=Adams |first2=Gregory |last2=Laughlin |name-list-style=amp |arxiv=astro-ph/9701131 |bibcode=1997RvMP...69..337A |date=April 1997|s2cid=12173790 }}</ref>{{rp|§§IIIE, IVA}}  Barrow and Tipler estimate that it would take 10<sup>15</sup> years for a white dwarf to cool to {{convert|5|K|C F|abbr=on}};<ref>Table 10.2, {{BarrowTipler1986}}</ref> however, if [[weakly interacting massive particle]]s (WIMPs) exist, interactions with these particles may keep some white dwarfs much warmer than this for approximately 10<sup>25</sup> years.<ref name="Adams"/>{{rp|§IIIE}} If protons are not stable, white dwarfs will also be kept warm by energy released from proton decay. For a hypothetical proton lifetime of 10<sup>37</sup> years, Adams and Laughlin calculate that proton decay will raise the [[effective temperature|effective surface temperature]] of an old one-[[solar mass|solar-mass]] white dwarf to approximately {{convert|0.06|K|C F|2|abbr=on}}. Although cold, this is thought to be hotter than the [[cosmic microwave background radiation]] temperature 10<sup>37</sup> years in the future.<ref name= "Adams" />

It is speculated that some massive black dwarfs may eventually produce [[supernova]] explosions. These will occur if [[Pycnonuclear fusion|pycnonuclear]] (density-based) fusion processes much of the star to [[nickel-56]], which decays into iron via emitting a [[positron]]. This would lower the [[Chandrasekhar limit]] for some black dwarfs below their actual mass. If this point is reached, it would then collapse and initiate runaway nuclear fusion. The most massive to explode would be just below the Chandrasekhar limit at around 1.41 solar masses and would take of the order of {{val|e=1100|u=years}}, while the least massive to explode would be about 1.16 solar masses and would take of the order {{val|e=32000||u=years}}, totaling around 1% of all black dwarfs. One major caveat is that [[proton decay]] would decrease the mass of a black dwarf far more rapidly than pycnonuclear processes occur, preventing any supernova explosions.<ref name=caplan2020>{{cite journal |doi=10.1093/mnras/staa2262 |title=Black dwarf supernova in the far future |year=2020 |last1=Caplan |first1=M. E. |journal=Monthly Notices of the Royal Astronomical Society |volume=497 |issue=4 |pages=4357–4362 |doi-access=free |arxiv=2008.02296 |bibcode=2020MNRAS.497.4357C |s2cid=221005728 }}</ref>

A more recent research has investigated "the evaporation rate and decay time of a non-rotating star of constant density due to spacetime curvature-induced pair production and apply this to compact stellar remnants such as neutron stars and white dwarfs". In particular, the authors find that the characteristic evaporation time scale for white dwarfs is ≥ {{val|e=78|u=years}}, much lower than previous estimations.<ref name=falcke2025>{{cite arXiv | eprint=2410.14734 | last1=Falcke | first1=Heino | last2=Wondrak | first2=Michael F. | last3=van Suijlekom | first3=Walter D. | title=An upper limit to the lifetime of stellar remnants from gravitational pair production | date=2024 | class=gr-qc }}</ref> However, other authors have pointed out that gravitational pair creation cannot take place for objects such as white or black dwarfs, so the lifetime of a black dwarf would probably be the one previously estimated.<ref name=ferreiro2024>{{cite journal |doi=10.1103/PhysRevLett.133.229001 |title=Comment on ''Gravitational Pair Production and Black Hole Evaporation'' |year=2024 |last1=Ferreiro |first1=A. |last2=Navarro-Salas |first2=J. |last3=Pla |first3=S. |journal=Physical Review Letters |volume=133 |issue=22 |pages=229001}}</ref>