Brown-dwarf desert
The brown-dwarf desert is a theorized range of orbits around a star within which
One of the many possible reasons for the existence of the desert relates to planetary (and brown dwarf) migration. If a brown dwarf were to form within 5 AU of its companion star, it could plausibly begin migrating inwards towards the central star and eventually fall into the star itself.[citation needed] That being said, the exact details of migration within a protoplanetary disk are not completely understood, and it is equally plausible that brown dwarf companions to FGK dwarfs would not undergo appreciable migration after their formation. A second possible reason is, depending on which formation paradigm is invoked, that a formation by core accretion should make the formation of higher mass brown dwarfs unlikely, as the gas accretion rate during runaway accretion onto high mass forming objects is reduced due to gap formation in the disk. The limited disk life time then truncates the mass range, limiting the maximum masses to approximately 10 Jupiter masses (MJ).[6] This effect might be somewhat mitigated by the fact that objects of 3–5 MJ and above might excite eccentric perturbations in the disk, allowing for non-negligible mass accretion even in the presence of a gap.[7] Objects that form further outside (a>80 AU), where the disk is prone to gravitational instabilities, might be able to reach the masses required to cross the planet–brown dwarf threshold.[8] For these objects it might be unlikely to migrate into the inner regions of the disk, however, due to the long type-II migration timescale for massive objects in the brown dwarf mass regime.[9]
See also
References
- ISBN 0-521-86015-6.
- S2CID 123539686
- doi:10.1086/587435
- ISSN 0004-637X.
- ISSN 0035-8711.
- S2CID 8619054.
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- ISBN 978-0-8165-2945-2.
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