A Y-Type Star, also known as a (Brown dwarf) are substellar objects that have more mass then the biggest gas giant planets, but less then the less massive main-sequence stars. Their mass, is approximately 13 to 80 times more then that of Jupiter, but not big enough to sustain nuclear fusion of ordinary hydrogen into helium in their cores.
An artist illustration of what a Y-Type Star (or Brown dwarf) would look like.