A brown dwarf is not really brown, but cherry-red. 


It’s not cold; I mean, it experiences molten iron rain, you don’t want to put your hand on it.  First discovered in 1995, they’re too big to be planets, but too small to be stars, and therefore too cool (surface < 2500 degrees C) to sustain significant nuclear fusion in their cores.  You need to be at least eight percent of the mass of our Sun if you want to be a star, and then you’d only just qualify as a red dwarf.  (Most stars are red dwarfs, actually.)   But a brown dwarf isn’t nothing; it’s still a brown dwarf.  It can fuse deuterium into helium for a while (a few million years), and to achieve that it had to be about ten Jupiters (.01 solar masses) or larger.  So that’s pretty respectable.  Luckily for anyone looking for brown dwarfs, they can keep on glowing after that initial fusion period is over because they release gravitational energy as they contract.