Final answer:
A T Tauri star is a young star that exhibits variable light and outflowing gas. They are formed from protostars and are observable only in the infrared region of the spectrum.
Step-by-step explanation:
A T Tauri star is a young star that exhibits variable light and outflowing gas. It is named after one of the best studied and brightest members of this class of stars, which was discovered in the constellation of Taurus. T Tauri stars are formed from protostars that are embedded in an envelope of dust and gas, and are observable only in the infrared region of the spectrum.
T Tauri stars are considered to be in a middle stage between protostars and hydrogen-fusing stars, like the Sun. Recent observations have revealed jets of material and stellar winds coming from some T Tauri stars, which provide evidence of interaction with their environment.