T-type stars are a class of celestial objects that fall under the category of brown dwarfs, which are substellar objects that are not massive enough to sustain hydrogen fusion like true stars. They are characterized by their cool temperatures, typically ranging from about 700 to 1,500 degrees Celsius. T-type stars emit most of their energy in the infrared spectrum, making them difficult to observe with standard optical telescopes. These stars are often associated with the presence of methane in their atmospheres, which contributes to their distinctive spectral features. T-type stars are important for studying the transition between stars and planets, as they help astronomers understand the formation and evolution of celestial bodies in the universe.