A newborn star typically goes through four stages of adolescence. It begins life as a protostar still enshrouded in its natal molecular cloud,accreting new fabric and developing a proto-planetary disc. Slowly, stellar winds and radiation blow away the surrounding shell of gas and dust, and the third stage,when the surrounding envelope has cleared, is called the T-Tauri phase. T-Tauri stars (the course is named after the first star of this type that was so identified) are less than approximately ten million years old, and provide astronomers with promising candidates in which to study the early lives of stars and planets. They were among the first young stars to be identified because the earlier stages,still embedded in their birth clouds, were blocked from optical observations by the dust. In the fourth stage, or the disk stops accreting and the source's radiation comes from the star's photosphere. T-Tauri stars produce strong X-rays,primarily by what is thought to be coronal activity much like the coronal activity in our own Sun, although in some cases a component might be coming from hot fabric in the dusty disk.
Source: phys.org