Space
What Are Brown Dwarfs? The Failed Stars Between Planets and Suns
Brown dwarfs sit between the heaviest planets and the lightest hydrogen-burning stars, at roughly 13 to 80 Jupiter masses. They fuse deuterium for a while, never sustain hydrogen fusion, and cool through spectral classes L, T, and Y. The coldest known, WISE 0855-0714, is near 225 to 260 K.