Brown dwarfs are objects that are too large to be called planets, but too small to be called stars. They are often described as "failed stars" because they do not have enough mass to sustain nuclear fusion in their cores. Brown dwarfs are still hot, however, and they emit light in the infrared spectrum.

The line that separates stars from brown dwarfs is not always clear. Some objects may have characteristics that are intermediate between the two. In general, however, astronomers consider an object to be a star if it has a mass of at least 0.08 solar masses. Objects with masses below this threshold are considered to be brown dwarfs.

Recent research has suggested that the dividing line between stars and brown dwarfs may need to be revised. Some astronomers believe that objects with masses as low as 0.013 solar masses may be able to sustain nuclear fusion. If this is true, then there would be many more brown dwarfs in the universe than we currently thought.

The debate over the definition of a star is still ongoing. As astronomers continue to learn more about these objects, the line that separates stars from brown dwarfs may become clearer.