Brown dwarf. Artwork of a brown dwarf star" with an orbiting planet (lower left). Brown dwarfs may be part of dark matter, the near-invisible material that makes up about 90% of the universe's mass. A brown dwarf is an object which began to accumulate material like a star but which never collected enough for nuclear reactions to begin in its core. Brown dwarfs are difficult to detect because they emit no real light of their own, and probably appear more like a large version of the planet Jupiter. They do shine weakly in the infrared range as their contraction releases energy."