Black dwarf

Last updated
For other uses, see Black dwarf (disambiguation).Not to be confused with black hole or black star (semiclassical gravity).
Diagram of stellar evolution, showing the various stages of stars with different masses Star Life Cycle Chart.jpg
Diagram of stellar evolution, showing the various stages of stars with different masses

A black dwarf is a theoretical stellar remnant, specifically a white dwarf that has cooled sufficiently to no longer emit 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 at the present time. The temperature of the coolest white dwarfs is one observational limit on the universe's age. [1]

Contents

The name "black dwarf" has also been applied to hypothetical late-stage cooled brown dwarfs – substellar objects with insufficient mass (less than approximately 0.07  M☉) to maintain hydrogen-burning nuclear fusion. [2] [3] [4] [5]

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 challenging 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 3,900 K (3,630 °C; 6,560 °F) (equivalent to 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 (which is yet to be proven to exist), 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 (−268.15 °C; −450.67 °F); [11] however, if weakly interacting massive particles (WIMPs) exist, interactions with these particles may 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 (−273.09 °C; −459.56 °F). Although cold, this is thought to be hotter than the cosmic background radiation temperature 1037 years in the future. [10]

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, it would then 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 also, 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 at least 1015 (1 quadrillion) years, though it could take much longer than this, if weakly interacting massive particles (WIMPs) exist, as described above. The described phenomena are considered a promising method of verification for the existence of WIMPs and black dwarfs. [13]

See also

Related Research Articles

The Chandrasekhar limit is the maximum mass of a stable white dwarf star. The currently accepted value of the Chandrasekhar limit is about 1.4 M☉ (2.765×1030 kg). The limit was named after Subrahmanyan Chandrasekhar.

<span class="mw-page-title-main">Dark matter</span> Concept in cosmology

In astronomy, dark matter is a hypothetical form of matter that appears not to interact with light or the electromagnetic field. Dark matter is implied by gravitational effects which cannot be explained by general relativity unless more matter is present than can be seen. Such effects occur in the context of formation and evolution of galaxies, gravitational lensing, the observable universe's current structure, mass position in galactic collisions, the motion of galaxies within galaxy clusters, and cosmic microwave background anisotropies.

<span class="mw-page-title-main">Neutron star</span> Collapsed core of a massive star

A neutron star is a collapsed core of a massive supergiant star. Stars that collapse into neutron stars have a total mass of between 10 and 25 solar masses (M☉), or possibly more for those that are especially rich in elements heavier than hydrogen and helium. Except for black holes, neutron stars are the smallest and densest known class of stellar objects. Neutron stars have a radius on the order of 10 kilometers (6 mi) and a mass of about 1.4 M☉. They result from the supernova explosion of a massive star, combined with gravitational collapse, that compresses the core past white dwarf star density to that of atomic nuclei.

<span class="mw-page-title-main">Star</span> Large self-illuminated object in space

A star is a luminous spheroid of plasma held together by self-gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night; their immense distances from Earth make them appear as fixed points of light. The most prominent stars have been categorised into constellations and asterisms, and many of the brightest stars have proper names. Astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. The observable universe contains an estimated 1022 to 1024 stars. Only about 4,000 of these stars are visible to the naked eye—all within the Milky Way galaxy.

<span class="mw-page-title-main">Supernova</span> Explosion of a star at its end of life

A supernova is a powerful and luminous explosion of a star. A supernova occurs during the last evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion. The original object, called the progenitor, either collapses to a neutron star or black hole, or is completely destroyed to form a diffuse nebula. The peak optical luminosity of a supernova can be comparable to that of an entire galaxy before fading over several weeks or months.

<span class="mw-page-title-main">Stellar evolution</span> Changes to stars over their lifespans

Stellar evolution is the process by which a star changes over the course of its lifetime and how it can lead to the creation of a new star. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is considerably longer than the current age of the universe. The table shows the lifetimes of stars as a function of their masses. All stars are formed from collapsing clouds of gas and dust, often called nebulae or molecular clouds. Over the course of millions of years, these protostars settle down into a state of equilibrium, becoming what is known as a main-sequence star.

<span class="mw-page-title-main">White dwarf</span> Type of stellar remnant composed mostly of electron-degenerate matter

A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to Earth's. A white dwarf's low luminosity comes from the emission of residual thermal energy; no fusion takes place in a white dwarf. The nearest known white dwarf is Sirius B, at 8.6 light years, the smaller component of the Sirius binary star. There are currently thought to be eight white dwarfs among the hundred star systems nearest the Sun. The unusual faintness of white dwarfs was first recognized in 1910. The name white dwarf was coined by Willem Jacob Luyten in 1922.

Weakly interacting massive particles (WIMPs) are hypothetical particles that are one of the proposed candidates for dark matter.

<span class="mw-page-title-main">Red dwarf</span> Dim, low mass stars on the main sequence

A red dwarf is the smallest kind of star on the main sequence. Red dwarfs are by far the most common type of fusing star in the Milky Way, at least in the neighborhood of the Sun. However, due to their low luminosity, individual red dwarfs cannot be easily observed. From Earth, not one star that fits the stricter definitions of a red dwarf is visible to the naked eye. Proxima Centauri, the star nearest to the Sun, is a red dwarf, as are fifty of the sixty nearest stars. According to some estimates, red dwarfs make up three-quarters of the fusing stars in the Milky Way.

Degenerate matter occurs when the Pauli exclusion principle significantly alters a state of matter at low temperature. The term is used in astrophysics to refer to dense stellar objects such as white dwarfs and neutron stars, where thermal pressure alone is not enough to avoid gravitational collapse. The term also applies to metals in the Fermi gas approximation.

In astronomy, the term compact object refers collectively to white dwarfs, neutron stars, and black holes. It could also include exotic stars if such hypothetical, dense bodies are confirmed to exist. All compact objects have a high mass relative to their radius, giving them a very high density, compared to ordinary atomic matter.

<span class="mw-page-title-main">Gravitational collapse</span> Contraction of an astronomical object due to the influence of its gravity

Gravitational collapse is the contraction of an astronomical object due to the influence of its own gravity, which tends to draw matter inward toward the center of gravity. Gravitational collapse is a fundamental mechanism for structure formation in the universe. Over time an initial, relatively smooth distribution of matter, after sufficient accretion, may collapse to form pockets of higher density, such as stars or black holes.

Supernova nucleosynthesis is the nucleosynthesis of chemical elements in supernova explosions.

<span class="mw-page-title-main">Type Ia supernova</span> Type of supernova in binary systems

A Type Ia supernova is a type of supernova that occurs in binary systems in which one of the stars is a white dwarf. The other star can be anything from a giant star to an even smaller white dwarf.

Carbon detonation or carbon deflagration is the violent reignition of thermonuclear fusion in a white dwarf star that was previously slowly cooling. It involves a runaway thermonuclear process which spreads through the white dwarf in a matter of seconds, producing a type Ia supernova which releases an immense amount of energy as the star is blown apart. The carbon detonation/deflagration process leads to a supernova by a different route than the better known type II (core-collapse) supernova.

<span class="mw-page-title-main">Quasi-star</span> Hypothetical early-universe star with a black hole core

A quasi-star is a hypothetical type of extremely massive and luminous star that may have existed early in the history of the Universe. They are thought to live around 7-10 million years. Unlike modern stars, which are powered by nuclear fusion in their cores, a quasi-star's energy would come from material falling into a black hole at its core. They were first proposed in the 1960s and have since provided valuable insights into the early universe, galaxy formation, and the behavior of black holes. Although they have not been observed, they are considered to be a possible progenitor of supermassive black holes.

<span class="mw-page-title-main">Future of an expanding universe</span> Future scenario if the expansion of the universe will continue forever or not

Current observations suggest that the expansion of the universe will continue forever. The prevailing theory is that the universe will cool as it expands, eventually becoming too cold to sustain life. For this reason, this future scenario once popularly called "Heat Death" is now known as the "Big Chill" or "Big Freeze".

<span class="mw-page-title-main">Primordial black hole</span> Hypothetical black hole formed soon after the Big Bang

In cosmology, primordial black holes (PBHs) are hypothetical black holes that formed soon after the Big Bang. In the inflationary era and early radiation-dominated universe, extremely dense pockets of subatomic matter may have been tightly packed to the point of gravitational collapse, creating primordial black holes without the supernova compression typically needed to make black holes today. Because the creation of primordial black holes would pre-date the first stars, they are not limited to the narrow mass range of stellar black holes.

p-nuclei (p stands for proton-rich) are certain proton-rich, naturally occurring isotopes of some elements between selenium and mercury inclusive which cannot be produced in either the s- or the r-process.

<span class="mw-page-title-main">O-type star</span> Stellar classification

An O-type star is a hot, blue-white star of spectral type O in the Yerkes classification system employed by astronomers. They have temperatures in excess of 30,000 kelvins (K). Stars of this type have strong absorption lines of ionised helium, strong lines of other ionised elements, and hydrogen and neutral helium lines weaker than spectral type B.

References

  1. 1 2 Heger, A.; Fryer, C. L.; et al. (2003). "How Massive Single Stars End Their Life". The Astrophysical Journal. 591 (1): 288–300. arXiv: astro-ph/0212469 . Bibcode:2003ApJ...591..288H. doi:10.1086/375341. S2CID   59065632 . Retrieved 25 March 2022.
  2. ↑ 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 .
  3. ↑ Kumar, Shiv S. (1962). "Study of Degeneracy in Very Light Stars". Astronomical Journal. 67: 579. Bibcode:1962AJ.....67S.579K. doi: 10.1086/108658 .
  4. ↑ Darling, David. "brown dwarf". The Encyclopedia of Astrobiology, Astronomy, and Spaceflight. David Darling. Retrieved May 24, 2007– via daviddarling.info.
  5. ↑ Tarter, Jill (2014), "Brown is Not a Color: Introduction of the Term 'Brown Dwarf'", in Joergens, Viki (ed.), 50 Years of Brown Dwarfs, Astrophysics and Space Science Library, vol. 401, Springer, pp. 19–24, doi:10.1007/978-3-319-01162-2_3, ISBN   978-3-319-01162-2
  6. ↑ Johnson, Jennifer. "Extreme Stars: White Dwarfs & Neutron Stars" (PDF). Ohio State University . Retrieved 3 May 2007.
  7. ↑ Richmond, Michael. "Late stages of evolution for low-mass stars". Rochester Institute of Technology. Retrieved 4 August 2006.
  8. ↑ 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.
  9. ↑ "12 Billion-year-old white-dwarf stars only 100 light-years away". spacedaily.com. Norman, Oklahoma. 16 April 2012. Retrieved 10 January 2020.
  10. 1 2 3 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.
  11. ↑ Table 10.2, Barrow, John D.; Tipler, Frank J. (1986). The Anthropic Cosmological Principle (1st ed.). Oxford University Press. ISBN   978-0-19-282147-8. LCCN   87028148.
  12. ↑ 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.
  13. ↑ Kouvaris, Chris; Tinyakov, Peter (2011-04-14). "Constraining asymmetric dark matter through observations of compact stars". Physical Review D. 83 (8): 083512. arXiv: 1012.2039 . Bibcode:2011PhRvD..83h3512K. doi:10.1103/PhysRevD.83.083512. ISSN   1550-7998. S2CID   55279522.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.