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Unlike brown dwarfstars, which are formed from the collapse of a gas cloud, planetars are planet-like objects that are formed in the manner of planets, through accretion or core collapse from a circumstellar disc. Both brown dwarfs and planetars are planet-like objects above a certain size. Astronomers are divided into two camps over whether to classify these planet-like objects separately depending on their formation process. Such a planet might also be referred to as a hypergiant planet.
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 planemo2M1207b has been discovered to harbour a disc.