An object less massive than a star, but heavier than a planet: A brown dwarf star is a theoretical "star" and does not have enough mass to ignite nuclear reactions at their centers, but shine by heat released during their contraction from a gas cloud.

Some astronomers believe that vast numbers of brown dwarf stars exist throughout the galaxy, but because of the difficulty in detecting them, none of them were discovered until 1995, when U.S. astronomers discovered a brown dwarf star in the constellation Lepus (Hare).