A sub-brown dwarf or planetary-mass brown dwarf is an astronomical object that formed in the same manner as stars and brown dwarfs (i.e. through the collapse of a gas cloud) but that has a mass below the limiting mass for thermonuclear fusion of deuterium (about 13 MJ). Some researchers call them free-floating planets whereas others call them planetary-mass brown dwarfs.
Sub-brown dwarfs are formed in the manner of stars, through the collapse of a gas cloud (perhaps with the help of photo-erosion) but there is no consensus amongst astronomers on whether the formation process should be taken into account when classifying an object as a planet. Free-floating sub-brown dwarfs can be observationally indistinguishable from rogue planets that originally formed around a star and were ejected from orbit, and on the other hand a sub-brown dwarf formed free-floating in a star cluster may get captured into orbit around a star. A definition for the term "sub-brown dwarf" was put forward by the IAU Working Group on Extra-Solar Planets (WGESP), which defined it as a free-floating body found in young star clusters below the lower mass cut-off of brown dwarfs.
Lower mass limit
The smallest mass of gas cloud that could collapse to form a sub-brown dwarf is about 1 Jupiter mass (MJ). This is because to collapse by gravitational contraction requires radiating away energy as heat and this is limited by the opacity of the gas. A 3 MJ candidate is described in the paper.
List of possible sub-brown dwarfs
Orbiting one or more stars
There is no consensus whether these companions of stars should be considered sub-brown dwarfs or planets.
Orbiting a brown dwarf
There is no consensus whether these companions of brown dwarfs should be considered sub-brown dwarfs or planets.
- WISE 0855–0714 3–10 MJ about 7 light years away
- S Ori 52
- UGPS J072227.51-054031.2 10–25 MJ 13 light years away
- Cha 110913-773444 5–15 MJ 163 light years away
- CFBDSIR2149-0403 4–7 MJ 130 light years away
- OTS 44 11.5 MJ 550 light years away
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- Working Group on Extrasolar Planets – Definition of a "Planet" POSITION STATEMENT ON THE DEFINITION OF A "PLANET" (IAU)
- Delorme, P.; et al. (December 2012). "CFBDSIR2149-0403: a 4–7 Jupiter-mass free-floating planet in the young moving group AB Doradus ?". Astronomy & Astrophysics. Bibcode:2012A&A...548A..26D. arXiv: . doi:10.1051/0004-6361/201219984.
- Luhman, K. L. (21 April 2014). "Discovery of a ~250 K Brown Dwarf at 2 pc from the Sun". The Astrophysical Journal Letters. 786 (2): L18. Bibcode:2014ApJ...786L..18L. arXiv: . doi:10.1088/2041-8205/786/2/L18.
- What is a Planet? Debate Forces New Definition, by Robert Roy Britt, 02 November 2000
- IAU WGESP, 'Position Statement on the Definition of "Planet"', 28 February 2003
- Boss, Alan P.; Basri, Gibor; Kumar, Shiv S.; Liebert, James; Martín, Eduardo L.; Reipurth, Bo; Zinnecker, Hans (2003), "Nomenclature: Brown Dwarfs, Gas Giant Planets, and ?", Brown Dwarfs, 211: 529, Bibcode:2003IAUS..211..529B
- Scholz, Alexander; Geers, Vincent; Jayawardhana, Ray; Fissel, Laura; Lee, Eve; Lafreniere, David; Tamura, Motohide (2009), "Substellar Objects in Nearby Young Clusters (Sonyc): The Bottom of the Initial Mass Function in Ngc 1333", The Astrophysical Journal, 702: 805, Bibcode:2009ApJ...702..805S, arXiv: , doi:10.1088/0004-637X/702/1/805
- Scholz, Aleks; Jayawardhana, Ray (2007), "Dusty disks at the bottom of the IMF", The Astrophysical Journal, 672: L49, Bibcode:2008ApJ...672L..49S, arXiv: , doi:10.1086/526340