Brown dwarfs live in the Twilight Zone. They neither fit the category of a star or a planet. (And even the color naming is odd, "brown" is a desaturated yellow pigment. Ultra-red is a better name choice for them).

Brown dwarfs are interstellar objects larger than Jupiter but smaller than the lowest-mass stars. Like stars, they collapse out of a cloud of gas and dust but do not have enough mass to sustain the fusion of hydrogen like a normal star. In building these objects, nature is indiscriminate as to whether they light up as stars or not after forming.

Like stars, brown dwarfs can be born in pairs and orbit about each other. A Hubble Space Telescope survey finds that the older a brown dwarf is, the less likely it is to have a companion dwarf. This implies that a binary pair of dwarfs is so weakly linked by gravity that they drift apart over a few hundred million years due to the pull of bypassing stars. Call them the "lonely red hearts" of the cosmos.