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A black dwarf is a theoretical stellar remnant, specifically a white dwarf that has cooled sufficiently that it no longer emits significant heat or light. Because the time required for a white dwarf to reach this state is calculated to be longer than the current age of the universe (13.8 billion years), no black dwarfs are expected to exist in the universe now, and the temperature of the coolest white dwarfs is one observational limit on the age of the universe.[1]

The name "black dwarf" has also been applied to hypothetical late-stage cooled brown dwarfs – substellar objects that do not have sufficient mass (less than approximately 0.08 M☉) to maintain hydrogen-burning nuclear fusion.[2][3][4][5]

Black dwarfs should not be confused with black holes or black stars.

Formation

A white dwarf is what remains of a main-sequence star of low or medium mass (below approximately 9 to 10 solar masses (M☉)) after it has either expelled or fused all the elements for which it has sufficient temperature to fuse.[1] What is left is then a dense sphere of electron-degenerate matter that cools slowly by thermal radiation, eventually becoming a black dwarf.[6][7] If black dwarfs were to exist, they would be extremely difficult to detect, because, by definition, they would emit very little radiation. They would, however, be detectable through their gravitational influence.[8] Various white dwarfs cooled below 3900 K (M0 spectral class) were found in 2012 by astronomers using MDM Observatory's 2.4 meter telescope. They are estimated to be 11 to 12 billion years old.[9]

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, it is not known precisely how long it will take white dwarfs to cool to blackness.[10]:§§IIIE, IVA Barrow and Tipler estimate that it would take 1015 years for a white dwarf to cool to 5 K;[11] however, if weakly interacting massive particles (WIMPs) exist, it is possible that interactions with these particles will keep some white dwarfs much warmer than this for approximately 1025 years.[10]:§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 1037 years, Adams and Laughlin calculate that proton decay will raise the effective surface temperature of an old one-solar-mass white dwarf to approximately 0.06 K. Although cold, this is thought to be hotter than the cosmic background radiation temperature 1037 years in the future.[10]:§IVB

It is speculated that some massive black dwarfs may eventually produce supernova explosions. These will occur if pycnonuclear (density-based) fusion processes much of the star to iron, which would lower the Chandrasekhar limit for some black dwarfs below their actual mass. If this point is reached, then it would collapse and initiate runaway nuclear fusion. The most massive to explode would be near 1.35 solar masses and would take of the order of 101100 years, while the least massive to explode would be about 1.16 solar masses and would take of the order 1032000 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.[12]
Future of the Sun

Once the Sun stops fusing helium in its core and ejects its layers in a planetary nebula in about 8 billion years, it will become a white dwarf and, over trillions of years, eventually will no longer emit any light. After that, the Sun will not be visible to the equivalent of the naked human eye, removing it from optical view even if the gravitational effects are evident. The estimated time for the Sun to cool enough to become a black dwarf is about 1015 (1 quadrillion) years, though it could take much longer than this, if weakly interacting massive particles (WIMPs) exist, as described above.
See also
Look up black dwarf in Wiktionary, the free dictionary.

Degenerate matter – Collection of free, non-interacting particles with a pressure and other physical characteristics determined by quantum mechanical effects
Heat death of the universe – Possible fate of the universe

References

§3, Heger, A.; Fryer, C.L.; Woosley, S.E.; Langer, N.; Hartmann, D.H. (2003). "How massive single stars end their life". Astrophysical Journal. 591 (1): 288–300. arXiv:astro-ph/0212469. Bibcode:2003ApJ...591..288H. doi:10.1086/375341. S2CID 59065632.
Jameson, R. F.; Sherrington, M. R.; Giles, A.R. (October 1983). "A failed search for black dwarfs as companions to nearby stars". Monthly Notices of the Royal Astronomical Society. 205: 39–41. Bibcode:1983MNRAS.205P..39J. doi:10.1093/mnras/205.1.39P.
Kumar, Shiv S. (1962). "Study of Degeneracy in Very Light Stars". Astronomical Journal. 67: 579. Bibcode:1962AJ.....67S.579K. doi:10.1086/108658.
Darling, David. "brown dwarf". The Encyclopedia of Astrobiology, Astronomy, and Spaceflight. David Darling. Retrieved May 24, 2007 – via daviddarling.info.
Tarter, Jill (2014), "Brown is not a color: Introduction of the term 'Brown Dwarf'", in Joergens, Viki (ed.), 50 Years of Brown Dwarfs – From Prediction to Discovery to Forefront of Research, Astrophysics and Space Science Library, 401, Springer, pp. 19–24, doi:10.1007/978-3-319-01162-2_3, ISBN 978-3-319-01162-2
Johnson, Jennifer. "Extreme Stars: White Dwarfs & Neutron Stars" (PDF). Ohio State University. Retrieved 3 May 2007.
Richmond, Michael. "Late stages of evolution for low-mass stars". Rochester Institute of Technology. Retrieved 4 August 2006.
Alcock, Charles; Allsman, Robyn A.; Alves, David; Axelrod, Tim S.; Becker, Andrew C.; Bennett, David; et al. (1999). "Baryonic Dark Matter: The Results from Microlensing Surveys". In the Third Stromlo Symposium: The Galactic Halo. 165: 362. Bibcode:1999ASPC..165..362A.
"12 Billion-year-old white-dwarf stars only 100 light-years away". spacedaily.com. Norman, Oklahoma. 16 April 2012. Retrieved 10 January 2020.
Adams, Fred C. & Laughlin, Gregory (April 1997). "A Dying Universe: The Long Term Fate and Evolution of Astrophysical Objects". Reviews of Modern Physics. 69 (2): 337–372. arXiv:astro-ph/9701131. Bibcode:1997RvMP...69..337A. doi:10.1103/RevModPhys.69.337. S2CID 12173790.
Table 10.2, Barrow, John D.; Tipler, Frank J. (1986). The Anthropic Cosmological Principle 1st edition 1986 (revised 1988). Oxford University Press. ISBN 978-0-19-282147-8. LCCN 87028148.

Caplan, M. E. (2020). "Black dwarf supernova in the far future". Monthly Notices of the Royal Astronomical Society. 497 (4): 4357–4362. arXiv:2008.02296. Bibcode:2020MNRAS.497.4357C. doi:10.1093/mnras/staa2262. S2CID 221005728.

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White dwarf
Formation

Chandrasekhar limit PG 1159 star Stellar evolution Hertzsprung–Russell diagram Mira variable

Fate

Black dwarf Type Ia supernova
Candidates Neutron star
Pulsar Magnetar Related links Stellar black hole
Related links Compact star
Quark star Exotic star Extreme helium star Subdwarf B star Helium planet

In binary
systems

Nova
Remnant List Dwarf nova Symbiotic nova Cataclysmic variable star
AM CVn star Polar Intermediate polar X-ray binary
Super soft X-ray source Binary pulsar
X-ray pulsar List Helium flash Carbon detonation

Properties

Pulsating Urca process Electron-degenerate matter Quasi-periodic oscillations

Related

Planetary nebula
List RAMBOs White dwarf luminosity function Timeline of white dwarfs, neutron stars, and supernovae

vte

Stars
Formation

Accretion Molecular cloud Bok globule Young stellar object
Protostar Pre-main-sequence Herbig Ae/Be T Tauri FU Orionis Herbig–Haro object Hayashi track Henyey track

Evolution

Main sequence Red-giant branch Horizontal branch
Red clump Asymptotic giant branch
super-AGB Blue loop Protoplanetary nebula Planetary nebula PG1159 Dredge-up OH/IR Instability strip Luminous blue variable Blue straggler Stellar population Supernova Superluminous supernova / Hypernova

Spectral classification

Early Late Main sequence
O B A F G K M Brown dwarf WR OB Subdwarf
O B Subgiant Giant
Blue Red Yellow Bright giant Supergiant
Blue Red Yellow Hypergiant
Yellow Carbon
S CN CH White dwarf Chemically peculiar
Am Ap/Bp HgMn Helium-weak Barium Extreme helium Lambda Boötis Lead Technetium Be
Shell B[e]

Remnants

White dwarf
Helium planet Black dwarf Neutron
Radio-quiet Pulsar
Binary X-ray Magnetar Stellar black hole X-ray binary
Burster

Hypothetical

Blue dwarf Green Black dwarf Exotic
Boson Electroweak Strange Preon Planck Dark Dark-energy Quark Q Black Gravastar Frozen Quasi-star Thorne–Żytkow object Iron Blitzar

Stellar nucleosynthesis

Deuterium burning Lithium burning Proton–proton chain CNO cycle Helium flash Triple-alpha process Alpha process Carbon burning Neon burning Oxygen burning Silicon burning S-process R-process Fusor Nova
Symbiotic Remnant Luminous red nova

Structure

Core Convection zone
Microturbulence Oscillations Radiation zone Atmosphere
Photosphere Starspot Chromosphere Stellar corona Stellar wind
Bubble Bipolar outflow Accretion disk Asteroseismology
Helioseismology Eddington luminosity Kelvin–Helmholtz mechanism

Properties

Designation Dynamics Effective temperature Luminosity Kinematics Magnetic field Absolute magnitude Mass Metallicity Rotation Starlight Variable Photometric system Color index Hertzsprung–Russell diagram Color–color diagram

Star systems

Binary
Contact Common envelope Eclipsing Symbiotic Multiple Cluster
Open Globular Super Planetary system

Earth-centric
observations

Sun
Solar System Sunlight Pole star Circumpolar Constellation Asterism Magnitude
Apparent Extinction Photographic Radial velocity Proper motion Parallax Photometric-standard

Lists

Proper names
Arabic Chinese Extremes Most massive Highest temperature Lowest temperature Largest volume Smallest volume Brightest
Historical Most luminous Nearest
Nearest bright With exoplanets Brown dwarfs White dwarfs Milky Way novae Supernovae
Candidates Remnants Planetary nebulae Timeline of stellar astronomy

Related articles

Substellar object
Brown dwarf Sub-brown dwarf Planet Galactic year Galaxy Guest Gravity Intergalactic Planet-hosting stars Tidal disruption event

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