Planetar (astronomy)

Planetar (astronomy)

Planetar is a term used in astronomy that refers to one of two things:
* Brown dwarfs - objects intermediate in size between planets and stars.
* Interstellar planets - planetars that are cold masses smaller than brown dwarfs and do not orbit a star, but are free-floating in space.

Both definitions have been proposed, but neither has achieved wide usage in the astronomical and planetary science communities.

Brown dwarf planetars

Planetars are planet-like objects that are more massive than the low-mass cut-off for brown dwarfs. These generally are referred to as "brown dwarfs". However, a planetar is formed in the manner of planets, through accretion or core collapse from a circumstellar disc, and not through the collapse of a gas cloud. The distinction between a planetar and a brown dwarf is unclear, astronomers are divided into two camps as whether to consider the formation process of a planet as part of its division in classification. Such a planet might also be referred to as a "hypergiant planet".Fact|date=February 2007

Red dwarf planetars

Hypothetically an ultra-giant planet may result from planetary formation large enough to become a red dwarf. Perhaps even larger stars may form from discs of gas of Population III protostars.Fact|date=February 2007

Unbound planet planetars

Interstellar planetary mass objects, also known as planetars, are called such, because a portion of the astronomy community defines a planet as something that must orbit a star. Any planetary-mass object which does not orbit a star, cannot according to that rule be called a planet. As it exists alone like a star, it is called a planet-star, or shorter "planetar". In 2003, the IAU Extrasolar Planet Working Group recommended that these objects be called sub-brown dwarfs.

Some of these planemo harbour debris discs akin to proplyds. The planemo 2M1207b has been discovered to harbour a disc.

ee also

* Sub-brown dwarf
* Interstellar planet
* Brown dwarf
* Giant planet
* Planemo
* Fusor


* arXiv: [ Infrared Spectroscopy of Substellar Objects in Orion] "P. W. Lucas, P. F. Roche, France Allard, Peter H. Hauschildt" Mon, 14 May 2001 09:08:51 GMT (accessed: 25/08/2006)
* Royal Astronomical Society: [ FREE-FLOATING PLANETS CONFIRMED] Thursday, 29 March 2001 (accessed: 25/08/2006)
* [] (subscription required): [ Lonely planets float free] "Tom Clarke" 04 Apr 2001 (accessed: 25/08/2006)

External links

* [ Strange New Worlds Could Make Miniature Solar Systems] Robert Roy Britt ( 05 June 2006 11:35 am ET
* [ Working Group on Extrasolar Planets - Defintion of a "Planet"] POSITION STATEMENT ON THE DEFINITION OF A "PLANET" (IAU) 2003

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