What is "black dwarf"

in astrophysics, a kind of dead and lightless star, 1966.

n. (context astronomy English) a hypothesized white dwarf that has cooled down and no longer emits visible light

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 yet, and the temperature of the coolest white dwarfs is one observational limit on the age of the universe. A white dwarf is what remains of a main-sequence star of low or medium mass (below approximately 9 to 10 solar masses ) after it has either expelled or fused all the elements for which it has sufficient temperature to fuse. What is left is then a dense sphere of electron-degenerate matter that cools slowly by thermal radiation, eventually becoming a black dwarf. 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. Various white dwarfs cooled below 3900 K (M0 spectral class) have been found recently by astronomers using MDM Observatory's 2.4-meter telescope. They are estimated to be 11 to 12 billion years old.

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. Barrow and Tipler estimate that it would take 10 years for a white dwarf to cool to 5 K; however, if weakly interacting massive particles exist, it is possible that interactions with these particles will keep some white dwarfs much warmer than this for approximately 10 years. 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 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 10 years in the future.

The name black dwarf has also been applied to substellar objects that do not have sufficient mass, less than approximately 0.08 , to maintain hydrogen-burning nuclear fusion. These objects are now generally called brown dwarfs, a term coined in the 1970s. Black dwarfs should not be confused with black holes or neutron stars.

A black dwarf is a theoretical astronomical object.

Black Dwarf may refer to:

• Athanasius of Alexandria, called the Black Dwarf by his enemies
• The Black Dwarf (novel), Walter Scott's 1816 book in the Tales of my Landlord, 1st series
• The Black Dwarf (personage), David Ritchie (1740–1811), a Scottish dwarf and the basis for the title character in Sir Walter Scott's novel
• The Black Dwarf, Thomas Jonathan Wooler's satirical 19th century Radical journal
• The Black Dwarf (newspaper), a left-wing British journal of the 1960s, edited by Tariq Ali
• "Black Dwarf", a song by the Swedish doom metal band Candlemass on their album Candlemass
• Black Dwarf (comics), a fictional character in the Marvel Universe

David Ritchie (1740–1811), known also as David of Manor Water, Bow'd Davie, Crooked David, and most notably the Black Dwarf, was a dwarf, the son of a quarryman at the slate quarries of Stobo. He was the inspiration for Sir Walter Scott's novel, The Black Dwarf. Scott visited him in 1797.

He was brought up as a brushmaker in Edinburgh, but was disliked because of his appearance. He eventually settled in a stone cottage on the banks of Manor Water near the town of Peebles, Scotland. The door of the cottage was about 3 feet and 6 inches high, and the ceiling was just high enough for him to stand inside. The superstitious locals feared he could cast the evil eye on them, blamed him for any problems with their livestock, and generally avoided him.

He never wore shoes, which would not fit on his misshapen feet. Instead, he wrapped his legs and feet in cloth. He walked with the help of a staff considerably taller than himself.

Sources described him as being irritable and having a shrill, dissonant laugh, but he is also described as an intellectual who enjoyed reading Milton's Paradise Lost and ballads by William Shenstone.