|
|
To comply with Wikipedia's lead section guidelines, the introduction of this article may need to be rewritten. Please discuss this issue on the talk page and read the layout guide to make sure the section will be inclusive of all essential details. (May 2011) |
|
|
This article may require cleanup to meet Wikipedia's quality standards. No cleanup reason specified. Please add a |reason= parameter to this template. Please help improve this article if you can. The talk page may contain suggestions. (May 2011) |
In astronomy, a planetar is either of two things:
Both definitions have been proposed, but neither has achieved wide usage in the astronomical and planetary science communities. The term is a portmanteau: "planet"+"star".
|
Contents
|
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.[citation needed]
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.[citation needed]
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 planetar. In 2003, the IAU Extrasolar Planet Working Group recommended that these objects be called sub-brown dwarfs.
Some of these planemos harbour debris discs akin to proplyds. The planemo 2M1207b has been discovered to harbour a disc.
|
||||||||||||||||||||||||||||||||||||||||||||
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)