They frequently are found orbiting a star in what scientists call a binary arrangement, implying that they formed out of the original disk of gas and dust. Much of the current debate, therefore, centers on size. And when a brown dwarf is about 13 times the mass of Jupiter, it generates enough pressure to force the burning of deuterium, a hydrogen-like element. Planets cannot burn deuterium. This still leaves areas of confusion, allowing the possibility of some brown dwarfs that are less massive than other objects that would be classified as planets.
Brown dwarfs are the ill-defined middle ground between planets and stars.
A star is a star because it shines on its own, generating light through thermonuclear reactions in which hydrogen is converted to helium. But brown dwarfs can, like stars, be born out of an otherwise unorganized cloud of gas and dust, when gravity forces a direct collapse of the cloud. And even stars cross the blurry lines of definition. This happens in binary-star systems, where one star forms first and the other is created from the leftovers. In the paper, Basri discussed the two possible ways that free-floating planets, among the most vexing objects, might have formed.