Brown Dwarf — Brown dwarfs are a special type of low-mass star (approximately 13-70 Jupiter masses) that do not have nuclear fusion occurring in their cores during their time on the main sequence.
Early in their development most brown dwarf stars do have lithium fusion in their cores, and a lack of lithium is a test for low-mass objects that are suspected of being brown dwarfs. Many brown dwarfs continue to glow in the red and infrared after their lithium is exhausted.
This glow is from the leftover heat generated by their formation and by the earlier lithium fusion, and is thought to reach temperatures of 1,730°C in large, young brown dwarfs.
A few potential brown dwarf candidates have been detected, and they are thought to be the most common type of star in the Milky Way galaxy. Gas giant planets that form directly from a collapsing nebula rather than accreting from a protostellar disk like other planets are more properly termed brown dwarf stars.
Recent observations of known brown dwarf candidates have revealed a pattern of brightening and dimming of infrared emissions that suggests relatively cool, opaque cloud patterns obscuring the hot interior and stirred by winds. The weather on such bodies is thought to be extremely violent, comparable to but far exceeding Jupiter’s famous storms.