failed star

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brown dwarf

brown dwarf, in astronomy, celestial body that is larger than a planet but does not have sufficient mass to convert hydrogen into helium via nuclear fusion as stars do. Also called “failed stars,” brown dwarfs form in the same way as true stars (by the contraction of a swirling cloud of interstellar matter). True stars have enough mass (greater than 0.084 times that of the sun) to compress their core until the increasing temperature and pressure ignite the hydrogen fusion reaction, but brown dwarfs have only a relatively short period of deuterium (heavy hydrogen) burning before they cool and fade. Their coolness gives brown dwarfs two distinguishing characteristics: One is that most of the radiation they emit is in the infrared part of the spectrum; the other is that brown dwarfs can be distinguished by traces of lithium in their spectrum because, unlike true stars, brown dwarfs never get hot enough to burn the lithium that was in the interstellar cloud as it condensed.

Although they should exist in large numbers, brown dwarfs are difficult to find using conventional astronomical techniques because they are dim compared with true stars. A number of brown dwarfs have been identified, the first in the Pleiades star cluster in 1995. The first X-ray-emitting brown dwarf was detected in Chamaeleon dark cloud number I in 1998. A year later, several so-called methane dwarfs were discovered; these are thought to be older brown dwarfs that have cooled sufficiently over billions of years so that large amounts of methane could form in their atmospheres. The closest brown dwarf to Earth, Epsilon Indi B, less than 12 light-years from the Sun, was discovered in 2003.

Brown dwarfs belong to the “T dwarf” category of objects straddling the domain between stars and giant planets. Because brown dwarfs are typically 10–80 times the mass of Jupiter, some of the large extrasolar bodies discovered orbiting stars may be brown dwarfs rather than giant Jupiterlike planets. Observations of 100 young brown dwarfs in the Orion Nebula in 2001 strongly supported the theory that they originate as failed stars; many of the brown dwarfs were surrounded by disks of dust and gas that conceivably could condense and conglomerate to create planets orbiting them. Brown dwarfs are believed to play an important role in the process of stellar evolution. They may be an important component of the dark matter that along with dark energy accounts for some 95% of the mass of the universe.

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failed star

[¦fāld ′stär]
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
A brown dwarf, or "failed star", is an object more massive than a planet yet too small to trigger the thermonuclear reactions that power stars.
The body, about eight times as heavy as Jupiter, resides next to a failed star, a brown dwarf dubbed 2M1207 (SN: 5/7/05, p.
But the mass that a brown dwarf accumulates is not enough to ignite thermonuclear reactions in its core, resulting in a failed star that is very cool.
To a layman like me, it seems almost impossible that light reflected from a body that lies "much farther from the star than Pluto does from the sun" could be seen from Earth at a distance of 450 light years, when Pluto, only 6 light hours away, reflects so little light to Earth ("Stellar Question: Extrasolar planet or failed star?" SN: 4/9/05, p.
In the case of 2M1207b, the exoplanet has a mass four times that of Jupiter. The planet orbits 2M1207, a ( brown dwarf - a failed star that's too large to be a planet, but lacks the mass necessary to start nuclear fusion in its core - located five billion miles away.
Barely more massive than a planet itself, a failed star 500 light-years from Earth is nevertheless cloaked in a disk of gas and dust from which planets could coalesce.
Upon his success, McNeil reflected: "I find it simply stunning that a $1,000 scope, which I literally pieced together on my kitchen table, was able to detect a 21st-magnitude object whose identity as a failed star was announced only days before I arrived at TSP."
Kevin Luhman, Penn State's Associate Professor of Astronomy and Astrophysics classifies this object as a "brown dwarf" - an object that formed just like a star out of a massive cloud of duct and gas, but the mass that it accumulates is not enough to ignite thermonuclear reactions in its core, resulting in a failed star that is very cool.
According to International Astronomical Union standards, the heavier body is a failed star known as a brown dwarf.
At both Keck II and Gemini North, Liu and his colleagues took images of a failed star, or brown dwarf, orbiting a young, sun-like star at a distance that could be just slightly greater than that at which Saturn orbits our sun.
Washington, July 30 (ANI): Astronomers have discovered a very young brown dwarf (or failed star dubbed "PZ Tel B") in a tight orbit around a young nearby Sun-like star (PZ Tel A).
The object, known as GJ 758 B, could be either a large planet or a "failed star," also known as a brown dwarf.