Black dwarf

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In astrophysics, a black dwarf is a hypothetical late phase of stellar evolution . A black dwarf would be the last stage of a white dwarf when its energy delivered or the surface temperature is fallen so far that neither heat nor visible light to any significant extent radiated be.

If black dwarfs exist, they could hardly be detected by their lack of or very little radiation, but rather as bulky objects by the action of their gravity .

Originally, the term "black dwarf" was also used for those precursors of stars that do not have the necessary 0.08 solar masses to fuse hydrogen ; however, such objects have been known as brown dwarfs since the 1970s . Black dwarfs should also not be confused with black holes or neutron stars .

Conditions and duration of education

A white dwarf is the remnant of a in the main sequence remaining star of low or medium initial mass (below 9 to 10  solar masses ), after all the chemical elements that could he merge due to a sufficiently high temperature, fused has or repelled. The remaining mass of the white dwarf is a maximum of 1.44 solar masses due to the Chandrasekhar limit . This dense and degenerate matter slowly cools down through thermal radiation to eventually become a black dwarf.

Barrow and Tipler estimate 10-15  (i.e. one quadrillion) years for cooling to  5K . According to the prevailing opinion, the universe is not yet old enough to be able to produce black dwarfs; the temperatures of the coolest white dwarfs are only just beginning to match the observable age of the universe of around 13.7 billion years.

How long it would take for the white dwarfs to cool down is not exactly known, since their distant future development depends on the following hypotheses:, § IIIE, IVA.

  • If WIMPs (“weakly interacting massive particles” of dark matter ) exist, white dwarfs could keep themselves warm by interacting with these particles for a period of around 10 25  years. , § IIIE.
  • If the proton is not stable ( proton decay ), the white dwarfs would also be kept warm due to the resulting energy release. Using an assumed lifetime of the protons, Adams and Laughlin calculated that the proton decay would raise the effective temperature of an ancient white dwarf with about one solar mass to 0.06 K; although this is very cold, it will probably be warmer than the cosmic background radiation temperature in 10 37 years. , §IVB.

See also

Individual evidence

  1. ^ Charles Alcock, Robyn A. Allsman, David Alves, Tim S. Axelrod, Andrew C. Becker, David Bennett, Kem H. Cook, Andrew J. Drake, Ken C. Freeman, Kim Griest, Matt Lehner, Stuart Marshall, Dante Minniti, Bruce Peterson, Mark Pratt, Peter Quinn, Alex Rodgers, Chris Stubbs, Will Sutherland, Austin Tomaney, Thor Vandehei, Doug L. Welch: Baryonic Dark Matter: The Results from Microlensing Surveys . In: ASP Conference Series . 165, 1999, p. 362. bibcode : 1999ASPC..165..362A .
  2. ^ RF Jameson, MR Sherrington, and AR Giles: A failed search for black dwarfs as companions to nearby stars . In: Monthly Notices of the Royal Astronomical Society . October 1983, pp. 39-41. bibcode : 1983MNRAS.205P..39J .
  3. ↑ brown dwarf , entry in The Encyclopedia of Astrobiology, Astronomy, and Spaceflight , David Darling, accessed online May 5, 2008.
  4. ↑ Heger, A .; Fryer, CL; Woosley, SE; Langer, N .; Hartmann, DH: How Massive Single Stars End Their Life . In: Astrophysical Journal . 591, No. 1, 2003, pp. 288-300. bibcode : 2003ApJ ... 591..288H .
  5. ↑ Jennifer Johnson: Extreme Stars: White Dwarfs & Neutron Stars (PDF; 119 kB) Ohio State University . Retrieved May 3, 2007.
  6. ↑ Michael Richmond: Late stages of evolution for low-mass stars . Rochester Institute of Technology accessdate = 2006-08-04.
  7. ^ Table 10.2, The Anthropic Cosmological Principle , John D. Barrow and Frank J. Tipler, Oxford: Oxford University Press, 1986. ISBN 0-19-282147-4 .
  8. ^ A b c Fred C. Adams, Gregory Laughlin: A Dying Universe: The Long Term Fate and Evolution of Astrophysical Objects , arxiv : astro-ph / 9701131 .