Many astronomical objects play by clear rules and fit into neat categories, but brown dwarfs (celestial objects too massive to be mere planets, but too small to be real stars) continue to refuse to cooperate.
Astronomers recently studied a sample of 70 objects, ranging from Jupiter-mass planets to brown dwarfs that are right on the brink of stardom. By looking for a relationship between the mass of these objects and certain features of their star systems (like whether the host star contained elements heavier than helium, or how round the objects' orbits were), the researchers hoped to draw a clear line that divides massive objects that form like stars and smaller ones that form like planets. But they were destined for disappointment, because the actual universe is messy and complicated.
