Brown Dwarfs



Brown Dwarfs

Brown dwarfs may be thought of as failed stars. They are the missing link between low mass stars and gas planets such as Jupiter. They are not massive enough to fuse Hydrogen into Helium, and to suport themselves via thermonuclear burning, and so after formation, they become compressed, degenerate objects, and simply cool, and eventually fade away. Brown dwarfs have masses between 0.075 Msun and 0.013 Msun (between 23964 and 4327 Earths) and a radius similar to Jupiter (1 Rjup = 71492 km). The first genuine brown dwarfs were discovered in 1995 in the field and in the Pleiades, the same year as the first extrasolar planet around a solar-type star (the image above is of G229B, the first brown dwarf to be discovered).

 Hundreds of brown dwarfs are now known, mainly due to large area surveys in the optical (0.5-1.0 microns) and near-infrared (1-2.5 microns) wavelengths. These brown dwarfs fall into 2 types - the L dwarfs, which have dusty, cloudy atmospheres, and T dwarfs wich have clearer atmospheres dominated by methane.

 The majority of brown dwarfs that have been discovered are single free-floating objects in the field. Some of these are cooler than 500K, and look much more like planets, than stars. The remainder of the brown dwarfs are in open star clusters such as the Pleiades, Prasepe and Upper Scorpius. Some of these objects have masses as low as a few times that of Jupiter, and by studying their distribution, we can determine how they formed, and whether they are likely to have escaped the cluster over time.

Pleiades open star cluster
The 125 Million year old Pleiades open star cluster, and the locations of 3 brown dwarfs discovered using the UKIDSS Galactic Cluster survey.

The work of the Leicester group deals with the search for young and distant brown dwarfs in open clusters, including the Pleiades, Hyades, Praesepe, and Coma Ber. We are also searching for and investigating brown dwarfs in binary systems with white dwarfs. For more detailed information, please see the research highlights.

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