Transcript: Stars must be hot enough in their cores for fusion to occur, a temperature of about ten million Kelvin or higher. Objects lower than this boundary which corresponds to a mass of eight percent the mass of the Sun are called brown dwarfs. Brown dwarfs have a mass range from a few times the mass of Jupiter up to eighty Jupiter masses at which point an object becomes a star. If you imagine the hypothetical experiment of adding mass to a gas giant planet the following occurs. As the mass is increased from the size of Jupiter to several times the mass of Jupiter the object continues to get larger. From two or three times Jupiter mass up to eighty Jupiter masses, as more mass is added the brown dwarf actually gets smaller because of gravitational compression. At eighty Jupiter masses as more mass is added nuclear reactions kick in and the star puffs up and starts to become larger again with increasing mass. Thus there are natural divisions between planets, brown dwarfs, and stars.